Analysis of Erythropoietin (EPO)

Oxford, March 2017

Ludger EPO AnalysisErythropoietin (EPO) biologics generate substantial revenue for the biopharma industry and as their patents expire the market for EPO biosimilars is set to grow considerably. Analysis of the glycosylation of EPO is a challenging requirement for drug developers because this glycoprotein hormone exhibits significant heterogeneity and its high degree of sialylation and accompanying acetylation can significantly affect its therapeutic properties (particularly the circulation half-life).

At Ludger we have developed accurate and reliable methods for analysis of EPO. In the poster attached here (WCBP 2017) we focus on sialic acid analysis and demonstrate the use of our DMB sialic acid technology (LudgerTag DMB kit, LT-KDMB-A1) to obtain information on the relative levels of the N-acetyl, N-glycolyl and O-acetyl sialic acids. This information can be used in QC to monitor batch-to-batch variation, or for comparability studies.

We can also execute detailed characterisation studies of EPO using LC and MS to give you the information you require.
This includes site specific glycosylation analysis to determine the following:

  • percentage site occupancy for each N-glycan and O-glycan site
  • glycan profile for each glycosylation site, with GU and relative proportions
  • identification of glycans at each glycosylation site (by comparison to structures identified from released glycan analysis)

If you would like more information on the DMB sialic acid technology or our glycoprofiling services (including method transfer) please contact us:

Senior Scientist awarded PhD

Oxford, January 2017

Ludger Leiden Kozak PhD defenseWe are delighted to announce that our Senior Scientist Radoslaw Kozak has successfully defended his PhD thesis at the Leiden University Medical Center, The Netherlands.

Rad has been with Ludger since 2008 and for the past 6 years Ludger has supported his PhD which was undertaken in collaboration with the University of Leiden. His thesis is entitled: 'Rapid and sensitive methods for the analysis and identification of O-glycans from glycoproteins'. This work has led to improvements in Ludger's methods and technology for O-glycan analysis.

We all congratulate our new 'Dr' on his achievement.

Full thesis available online:

Rad (seated centre, with paranymphs Stephanie Holst and Albert Bondt)
Photo by Gerhild Zauner

Innovate UK Grant: MODY diabetes

Oxford, January 2017

Innovate UK LogoLudger is delighted to have been awarded the Biomedical Catalyst 2016 - Feasibility Study grant funding from Innovate UK, for a glycomics precision diagnostic assay for Maturity Onset Diabetes of the Young (MODY).

MODY affects 1-4% of the diabetes patient population and it is estimated that at least 90% MODY patients are misdiagnosed and therefore, often prescribed ineffective treatment. A clinical diagnostics ‘MODY’ assay has been developed to identify patients with the most common form of MODY, HNF1A-type. These patients have reduced plasma outer arm fucosylation which is caused by defects in the HNF1A gene. The MODY assay is a plate based biochemical assay which provides a faster and more affordable alternative to genetic testing.

This exciting project, named GlycanDx-MODY, will be led by Ludger Ltd and includes the following partners; Genos (Croatia) and OCDEM (Oxford University, UK). The goal is to develop a clear business and technology plan for this assay to facilitate its incorporation into a diagnostic pathway for MODY which will ultimately be adopted by healthcare providers at the primary care level.

New publication in Nature Communications on Inflammatory Bowel Disease

Oxford, January 2017

Ludger IBD Nature CommunicationsAn article entitled ‘Integrative epigenome-wide analysis demonstrates that DNA methylation may mediate genetic risk in inflammatory bowel disease’ has been published in Nature Communications. Ludger is a member of the IBD-Biom consortium which contributed to the work.

Citation: Integrative epigenome-wide analysis demonstrates that DNA methylation may mediate genetic risk in inflammatory bowel disease. N. T. Ventham, N. A. Kennedy, A. T. Adams, R. Kalla, S. Heath, K. R. O'Leary, H. Drummond, IBD BIOM consortium, IBD CHARACTER consortium, D. C. Wilson, I. G. Gut, E. R. Nimmo & J. Satsangi. Nature Communications 7, Article number: 13507 (2016); doi:10.1038/ncomms13507.

Article link:

Grant news: GlySign

Oxford, November 2016

Ludger - GlySignWe are delighted to announce that the GlySign project has begun. GlySign is a research training network on glycomic clinical markers and assay development for Precision Medicine. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 722095

We are joined in the GlySign consortium by Genos and Leiden University Medical Center, and will shortly be recruiting two PhD students to be based at Ludger.

For more information please visit:

If you are interested in applying for a PhD position please visit:

Release of O-linked glycans from glycoprotein therapeutics

Oxford, October 2016

Ludger Orela KitLudger offers two Ludger Liberate kits that can be used to release of O-glycans from glycoprotein therapeutics; the Hydrazinolysis kit, LL-HYDRAZ-A2 and the Orela kit, LL-Orela-A2. Whilst hydrazinolysis is the gold standard method to remove all O-links, the Orela Kit contains reagents which are safer and much easier to handle.

O-glycans released using either of these kits have free reducing termini so are compatible with reducing-end labeling using reagents such as 2-aminobenzamide (2AB), 2-aminobenzoic acid (2AA) and Procainamide (Proc) allowing high-performance liquid chromatography (UHPLC) with fluorescent detection.

The Orela kit (Cat # LL-Orela-A2) can be used for up to 12 samples. Each kit includes LC-CEX cation exchange cartridges for O-glycan purification prior to fluorescent labeling.

The hydrazinolysis kit (Cat# LL-HYDRAZ-A2) can be used for up to 12 samples. The release conditions can be optimized for release of N-glycans, O-glycans or both N- and O-glycans. Each kit includes LC-CEX cation exchange cartridges for O-glycan purification and also LC-EB20 cartridges for N-glycan purification.

Ludger Liberate glycan release kits can be incorporated into a workflow for O glycan analysis in your labs:

n.b. exoglycosidase sequencing can be used to gain more detailed information on the O-glycan structures

New publication in Analytical Chemistry on High Throughput Permethylation

Oxford, August 2016

Ludger Permethylation Analytical ChemistryLudger has published an article in Analytical Chemistry presenting an automated and high throughput (HT) glycan sample preparation and permethylation method used for characterisation and relative quantitation of glycans, glycoprotein standards and biopharmaceutical samples (IgG4 and rhEPO). To our knowledge, this is the first largely automated workflow for permethylation that has been executed using a liquid handling robot and a commercially available kit. The matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) profiles obtained showed good agreement with hydrophilic liquid interaction chromatography (HILIC) and ultrahigh performance liquid chromatography (UHPLC) data (which is referred to as the gold standard method for glycan analysis). Automated permethylation and extraction of 96 glycan samples was achieved in less than 5 h and automated data acquisition on MALDI-TOF-MS took on average less than 1 min per sample, making this method convenient, fast, and reliable.

Citation: Automated High-Throughput Permethylation for Glycosylation Analysis of Biologics Using MALDI-TOF-MS. Archana Shubhakar, Radoslaw P. Kozak, Karli R. Reiding, Louise Royle, Daniel I. R. Spencer, Daryl L. Fernandes, and Manfred Wuhrer. Analytical Chemistry Article ASAP; DOI: 10.1021/acs.analchem.6b01639.

Pubmed link:

Hydrophilic interaction amide clean up cartridges

Oxford, July 2016

Ludger Scientific ReportsLudger's LudgerClean A cartridges are hydrophilic interaction amide cartridges (Cat # LC-A-24) which can be used for a number of applications, including clean up of:

  • 2AA/or 2AB labelled N glycans
  • VTag labelled glycopeptides
  • APTS labelled N-glycans

Each pack of LC-As contains 24 cartridges.
To order or request a quotation, contact

Study of Immunoglobulin A glycosylation in pregnancy: results published in Nature Scientific Reports

Oxford, June 2016

Ludger Scientific ReportsLudger has worked in collaboration with the Department of Rheumatology, Erasmus University Medical Center, Rotterdam, The Netherlands and Leiden University Medical Centre, The Netherlands to study IgA glycosylation in pregnancy.
Serum samples were taken at different stages of pregnancy and after delivery from a cohort of 29 women. A high-throughput workflow was adopted for the simultaneous analysis of serum-derived IgA1 N- and O-glycopeptides using matrix-assisted laser/desorption ionisation Fourier transform ion cyclotron resonance (MALDI-FTICR) mass spectrometry (MS).
Pregnancy associated changes of N-glycan bisection were found to be different for IgA1 compared to IgG-Fc. This method could be used for larger patient cohorts to study IgA N- and O-glycosylation changes in pathologies.

Citation: Bondt, A. et al. Longitudinal monitoring of immunoglobulin A glycosylation during pregnancy by simultaneous MALDI-FTICR-MS analysis of N- and O-glycopeptides. Sci. Rep. 6, 27955;doi: 10.1038/srep27955 (2016).

Link to full-text publication

New Publication: Site-specific N-glycosylation analysis of HIV-1 Envelope Glycoprotein

Oxford, March 2016

Ludger Ceramide Glycanase EnzymeThe trimeric HIV type 1 (HIV-1) envelope glycoprotein (Env) is targeted by broadly neutralizing antibodies (bNAbs) produced by the immune system during infection. As part of our collaboration with Max Crispin and his group at the University of Oxford, UK, we have performed site-specific N-glycosylation analysis of the gp120 and three gp41 subunits of Env. Using MALDI-MS, LC-MS and HILIC-UPLC our results uncovered a dominance of oligomannose-type glycans and revealed a mosaic of glycan microclusters bearing under-processed glycans, especially in areas covering the gp120 outer domain and at the trimer interfaces. This information will assist in the design of Env-based vaccine immunogens.

The work has now been published in Cell Reports:

Link to full-text publication

R&D at Ludger

Oxford, February 2016

Ludger Ceramide Glycanase EnzymeLudger has an ongoing Research and Development programme dedicated to improving glycan analysis for biopharmaceuticals and medical glycomics. Around half of our R&D is funded by EU grants as part of collaborative research programmes.

To find out more about these exciting projects please visit our R&D page

Here you will also find a full list of recent scientific posters as well as articles and publications and talks and presentations

LudgerZyme™ Ceramide Glycanase Enzyme

Oxford, February 2016

Ludger Ceramide Glycanase EnzymeGlycosphingolipids (GSLs) are implicated in the pathogenesis of various diseases including Fabry disease, Gaucher disease , Tay-Sachs disease and Sandhoff disease . The enzyme ceramide glycanase can be used for the characterisation of GSLs as it deglycosylates a variety of GSLs by cleaving the β-glycosyl linkage. Once free, the GSL glycans can be fluorescently labelled using LudgerTag labelling technology and then analysed to identify their glycosylation patterns.

Ludger’s ceramide glycanase kit (LZ-CER-HM-KIT) contains purified ceramide glycanase enzyme, buffer and and GM1 glycolipid. The kit is sufficient to deglycosylate 25 samples.

Cat # LZ-CER-HM-KIT     LudgerZyme™ Ceramide Glycanase Enzyme

To request a quote please contact

Permethylation of glycans

Oxford, February 2016

ludger permethylation kitPermethylation is the most popular technique for the derivatisation of carbohydrates for MALDI-MS detection, as it enhances ionization efficiency, stabilizes the sialic acids and aids linkage analysis studies. On average one sample can take as little as 1 minute for data acquisition using MALDI-MS, making it appealing for Quality by Design (QbD) and biomarker studies. Since the conventional in-solution technique to permethylate glycans is labour intensive with long turnaround times, we have developed a microplate-based permethylation kit to give you a cost effective, high throughput and reliable method.

Our new LudgerTag kit, LT-PERMET-96, can be used to process 1-96 samples using either a manual method or an automated method that has been adapted to a liquid handling robot. LT-PERMET-96 gives excellent signal enhancement due to increased ionization efficiency and the technology has been validated according to ICH Q2 (R1) guidelines (for Analytical Validation). Intra assay repeatability CVs for relative % intensities were ≤12% for major N-glycans from human IgG with a relative % areas of ≥ 5%.The results from validation studies suggest that this permethylation technique gives data that is comparable to UHPLC from 2-AB labelled and procainamide labelled glycans.

We also sell a Pre-Permethylation Clean-up Plate (Cat# LC-PERMET-96) for enrichment of released N-glycans before the permethylation step, as well as the following permethylated human IgG glycan standards, which can be used as system suitability standards and/or as calibration standards for MALDI-TOF-MS analysis:

For more information or pricing on any of these products please contact
Click here to view a poster presentation on the subject, and you can also view a full list of Ludger's recent scientific posters.

Summary of Glycan Cleanup Techniques

Oxford, November 2015

We offer a range of LudgerClean products to suit your specific need. The table below summarises the different applications.

ludger glycan cleanup table
click to enlarge

For additional technical advice, contact
Orders can be sent to

'How well is your column performing?'

Oxford, October 2015

ludger application 												            note on column performance

No matter what type of chromatography you are using (HILIC-LC for glycan GU, WAX-LC for glycan charge; RP-LC for sialic acid ormonosaccharide analysis) it is good practice to run a regular system suitability check.

Are you tracking your column performance? If not, please see the attached Ludger Application Note for guidance.

Contact us for more information at:

Purified Glycan Standards

Oxford, September 2015

Ludger produces a comprehensive range of purified glycans, including IgG glycans, which are used as standards during the analysis of biopharmaceuticals.

Purity acceptance criteria is 85% as determined by HILIC chromatography of the 2AB labeled glycans. HPAE-PAD chromatography, MALDI mass spectrometry and NMR analysis are also performed as supporting data.

In the examples here we have given their short names and Ludger product names:

Short Name
Oxford Notation Ludger Product
G0 A2 NGA2
G1 A2G1 A2G1
G2 A2G2 NA2

For the full list of these and other glycans (unlabeled, permethylated or labeled with 2AB, 2AA, procainamide or APTS), please visit

If you are unsure if we have the standard you are looking for, please contact us at

HIV-1 Publication in Nature Communications

Oxford, July 2015

We are delighted to announce that our collaboration with Dr Max Crispin and colleagues at the Oxford Glycobiology Institute, University of Oxford, UK, has resulted in a publication in Nature Communications. The paper is entitled "Glycan clustering stabilizes the mannose patch of HIV-1 and preserves vulnerability to broadly neutralizing antibodies".

The HIV-1 envelope glycoprotein gp120 is essential for virus entry into cells as it attaches to specific cell surface receptors. Whilst glycans on gp120 can protect the virus from antibody-mediated neutralization, a 'mannose patch' of under-processed oligomannose-type structures can also be a target for potent broadly neutralizing antibodies (bnAbs). Glycosylation site analysis on gp120 was performed using methods developed at Ludger. The contribution of individual glycosylation sites in the formation of the mannose patch is discussed in this publication, and supports the use of the mannose patch as a target for vaccine design.

Contact us for more information on Ludger's glycosylation site analysis service,

Ludger V-TAG Glycopeptide Labeling and Enrichment Kit

Oxford, March 2015

We are pleased to announce the launch of a kit for the labeling and enrichment of IgG glycopeptides, enabling analysis by (U)HPLC or MALDI Mass Spectrometry.

The VTAG kit (Cat # LT-VTAG-24) is suitable for IgG subclass glycoproteins that have been digested with pronase or trypsin to release the glycopeptides. As little as 5ug IgG sample can be used. The VTAG kit labels each sample in 1 hour and enriches the sample using a solid phase extraction (SPE) device for a further hour.

This kit has been validated according to ICH guideline Q2 (R1) guidelines. Using different IgG samples and replicates of 9 for each, CVs for repeatability were typically <5%.

Cat #

LT-VTAG-24     LudgerTag™ V-Tag Glycopeptide Labeling and Enrichment Kit

To request a quote please contact

Ludger Procainamide Labeling Kit

Oxford, February 2015

Procainamide labeling permits glycan identification by either mass spectrometry or UHPLC, and because of its improved ionisation efficiency compared to 2AB labeling it can permit identification of minor glycans (>1% relative peak area) by ESI-MS.

We are delighted to announce the launch of a Ludger kit for labeling glycans with procainamide (using 2PB as a reductant in place of sodium cyanoborohydride), along with a post-labeling clean up plate for the samples. This technology has been validated in house at Ludger; typical CVs for triplicate analyses were <5%.

Cat #

LT-KPROC-VP24     LudgerTag™ PROC (procainamide) Glycan Labeling Kit containing 2-picoline borane

To request a quote please contact

Does Long Term Storage Affect Glycosylation of Biotherapeutics?

Oxford, October 2013

Ludger has been working in collaboration with Arecor Ltd to study the effect of storage conditions on the glycosylation of biotherapeutics. Following long term storage at elevated temperatures in Arecor’s formulation technology Arestat™, the N-glycosylation profiles of EPO and IgG were obtained. Results showed that Arecor’s technology maintains glycosylation profiles of EPO or IgG after prolonged storage at elevated temperature.

If you would like more information about this or would like to discuss how we can help you to monitor your biopharmaceutical’s glycosylation, please contact

Permethylated IgG glycan standards for MS analysis

Oxford, October 2013

Structural analysis of carbohydrates is a requirement for biopharmaceutical characterisation and may include the determination of the following features: molecular mass, composition of monosaccharides and their configurational and conformational isomers, sequence of monosaccharide residues, presence and position of branches and functional groups and interglycosidic linkages.

Mass spectrometry is a useful tool in determining the molecular weights but the sensitivity can be low especially where there are many different structures. Carbohydrates often contain carboxy, amino, sulphate, and phosphate groups and both the nature and the position of these groups on the residue and the position of this residue within the glycan may be difficult to determine. Permethylation of glycans converts hydrogen groups to methyl groups which renders the glycans hydrophobic; the conversion stabilises sialic acids and can increase signal intensity in mass measurements.

Ludger now offers a permethylated IgG glycan library to use as a system suitability standard during MS analysis. Ludger also offers a C13 version of the standard which can be used as an internal standard in the same MALDI chip spot as your C12 labelled permethylated glycans.

Cat #

CPM-C13-IGG-01     N-glycan IgG library, permethylated with heavy (13C) MeI
CPM-IGG-01   N-glycan IgG library, permethylated

To request a quote or place an order please contact

LudgerSep™ C Buffer x4 concentrate for HPLC separation of sialylated, phosphorylated and sulphated glycans.

Oxford, September 2013

Many glycoproteins contain sialylated, sulphated or phosphorylated sugars, including drugs containing Mannose-6-Phosphate (Man6P). Man6P is a key targeting signal for acid hydrolase precursor proteins that are destined for transport to lysosomes and is present in therapeutic enzymes (enzyme replacement therapies) developed for treatment of lysosomal storage diseases.

Ludger has produced an ammonium formate buffer concentrate with a pH of 9 (above the pKa for phosphated glycans), which allows good separation of all anionic glycans (sialic acids, phosphorylated and sulphated sugars) using an anion exchange column.

This concentrate (Cat# LS-C-BUFFX4) simplifies the preparation of solvent for anion exchange, whilst avoiding the variations in buffer pH between batches which could lead to out-of-specification problems during glycan analysis. Simply dilute with water, add acetonitrile and use directly as an HPLC elution gradient when performing glycan analysis using the LudgerSep C3 column, Cat # LS-C3-7.5x75.

To request a quote or place an order please contact

LudgerTag™ 2AB and 2AA Glycan Labelling within 2 hours

Oxford, March 2013

Ludger is delighted to announce that using the LudgerTag™ VP24 kits, glycans can be labelled with 2-aminobenzamide (2-AB) or 2-aminobenzoic acid (2-AA) within 2 hours. These kits incorporate 2-picoline borane (2-PB) reductant, a safer alternative than standard sodium cyanoborohydride. This technology has now been patented and exclusively licenced to Ludger Ltd.

The kits have been validated following ICH Q2(R1) guidelines and beta-tested in the field. Precision values were excellent, with CVs of <5% for peaks with relative areas over 5% and CVs of <8% for peak with relative areas less than 5%. The kits offer equivalent labelling efficiency as standard LudgerTag™ 2AA and 2AB labelling kits containing sodium cyanoborohydride.

Ordering information:

LudgerTag™ 2-AB labelling kit with 2PB Cat# LT-KAB-VP24

LudgerTag™ 2-AA labelling kit with 2PB Cat# LT-KAA-VP24

To request a quote or place an order please contact

LudgerTag™ 2AB and 2AA Glycan Labelling Kits with Non Toxic Reductant

Oxford, November 2012

Fluorescent labelling methods for glycoprofiling of therapeutic glycoproteins are well established and aid subsequent separation and quantitation using a range of techniques. These include high performance liquid chromatography (HPLC and UHPLC), capillary electrophoresis (CE), and mass spectrometry. Of the fluorescent labels available, 2-aminobenzamide (2-AB) and 2-aminobenzoic acid (2-AA) are most widely used for oligosaccharide profiling. Existing 2-AA and 2-AB labelling kits use sodium cyanoborohydride as a reducing agent during glycan labelling. This reagent is toxic so a fume cupboard should be used during handling.

Following on from research performed by Ludger Ltd. in collaboration with Leiden University Medical Centre, The Netherlands, we have developed labelling kits containing a different and non-toxic reducing agent, 2-picoline borane (2-PB). This technology has now been patented and Ludger is delighted to offer two new kits for labelling glycans with either 2-AB (Cat# LT-KAB-VP24) or 2-AA (Cat# LT-KAA-VP24).

The kits have been validated following ICH Q2(R1) guidelines and beta-tested in the field. Precision values were excellent, with CVs of <5% for peaks with relative areas over 5% and CVs of <8% for peak with relative areas less than 5% (see Figure 1). The kits offer equivalent labelling efficiency as standard LudgerTag™ 2AA and 2AB labelling kits containing sodium cyanoborohydride (Figure 2).

Each kit comprises two premixed bottles; one containing acetic acid and DMSO solution and the other containing 2-AB or 2-AA label combined with 2PB. This makes the labelling process simpler. Labelling can also be performed within 2 hours.

Ordering information:

LudgerTag™ 2-AB labelling kit with 2PB Cat# LT-KAB-VP24

LudgerTag™ 2-AA labelling kit with 2PB Cat# LT-KAA-VP24

To request a quote or place an order please contact

Quantitative Glycopeptide Standard for Accurate Monosaccharide or Sialic Acid Quantitation

Oxford, November 2012

Quantitative sialic acid or monosaccharide analysis is an important step for developers and manufacturers of biologic drugs. Regulators are putting increasing pressure on companies to perform accurate glycoprofiling on their biopharmaceuticals. These analyses fall within ICH guidelines Q6B and Q5Efor comparability studies during product development and after major manufacturing changes. Furthermore, the recent EMA monograph on monoclonal antibodies and forthcoming USP chapters <1084> and <1094>on glycosylation analysis reinforce the need to perform glycoprofiling throughout the drug life cycle. Until now the difficulty with accurately quantifying sialic acids or monosaccharides has been the lack of quantitative standards.

Ludger Ltd. has produced a purified glycopeptide standard, the first in a range of Ludger BioQuant™ quantitative standards, which can be used as an internal standard and positive control when performing sialic acid or monosaccharide analyses in house. This particular Ludger BioQuant™ Standard (Cat# BQ-GPEP-A2G2S2-10U) is a complex biantennary N-linked glycan terminating in two N-acetylneuraminic acids.

Purity of >90% has been assessed by HPLC, correct mass identity assessed by MALDI mass spectrometry. The exact amount of material has been determined by quantitative NMR (qNMR) and quantitative monosaccharide analysis (MA). Quantity values by qNMR and MA agree within 90-110%.  MA is traceable to internationally accepted references from USP and dispensed using NIST traceable labware. qNMR is traceable to a NIST SRM traceable CRM analysed to the ISO 17025 standard. A detailed certificate of analysis is given for each standard. This contains comprehensive documentation, lot-specific values, expiration date and storage information.

The BioQuant GPEP-A2G2S2 standard can be used during the sialic acid or monosaccharide release and labeling process. This will enable you to check the efficiency of glycan release, labeling and recovery and will give you confidence in the accuracy of your sialic acid or monosaccharide measurements.

To request a quote or place an order please contact

Protein O-Glycosylation Analysis Review

Oxford, August 2012

Following the collaboration of Ludger with the University of Leiden, we are delighted to announce a publication in the journal Biological Chemistry.

This informative review describes the current methods available for analysis of O-glycosylation and discusses challenges that need to be met in the future. Areas covered include: analysis of released O-glycans, analysis of formerly O-glycosylated peptides (in order to give information on O-glycan attachment sites), and analysis of O-glycopeptides. Particular emphasis is given to MS fragmentation techniques such as collision-induced fragmentation, electron capture dissociation, and electron transfer dissociation.


Gerhild Zauner, Radoslaw P. Kozak, Richard A. Gardner, Daryl L. Fernandes, André M. Deelder and Manfred Wuhrer. Biol. Chem., Vol. 393, pp. 687–708, August 2012