Materials

The recombinant rhEPO BRP (presently batch 4.0) was acquired from EDQM (European Directorate for the Quality of Medicines). It is a 50:50 blending of epoetin alpha and epoetin beta⁵³, supplied at 13,000 IU per vial. Epoetin beta was acquired from Roche and supplied at 30,000 IU per syringe. It is a recombinant form of erythropoietin marketed under the trade name NeoRecormon, produced by recombinant DNA technology using Chinese hamster ovary cells as expression system. Epoetin zeta (Retacrit, Hospira) is a biosimilar to the reference medicinal product Eprex (Epoetin alpha), produced in Chinese hamster ovary cells. The Uniprot code for rhEPO is {"type":"entrez-protein","attrs":{"text":"P01588","term_id":"119526"}}P01588. Human blood plasma properdin (Uniprot code: {"type":"entrez-protein","attrs":{"text":"P27918","term_id":"464473"}}P27918) was obtained from Complement Technology, Inc. (TX, USA). Urea, dithiothreitol (DTT) and iodoacetamide were purchased from Sigma-Aldrich (Steinheim, Germany). Formic acid (FA) was purchased from Merck (Darmstadt, Germany). Acetonitrile (ACN) was purchased from Biosolve (Valkenswaard, The Netherlands). Sequencing grade trypsin was obtained from Promega (Madison, WI, USA). Glu-C, Asp-N, PNGase F and Sialidase were obtained from Roche (IN, USA).