What accounts for the charge difference in recombinant human erythropoietin (EPO) compared to endogenous material?
I wonder if changes to recombinant EPO would make it harder to detect doping. As I understand it, doping with EPO by athletes is detected using isoelectric focusing, relying on a charge difference between endogenous and recombinant EPO.
The answer probably lies in one of these papers below, but I am no longer affiliated with a research institution or university so it's harder to get primary sources.
Wide L, Bengtsson C. (1990) Molecular charge heterogeneity of human serum erythropoietin. Br J Haematol 76:121–7.
Wide L, Bengtsson C, Berglund B, Ekblom B. (1995) Detection in blood and urine of recombinant
erythropoietin administered to healthy men. Med Sci Sports Exer 27:1569–76
This letter and response
(PDF) from 2003 hints that glycosylation might account for the difference, but the situation is complicated by differences between serum EPO and that found in urine.