Why is recombinant EPO differently charged?
As far as I know, previously EPO was made using blood material of hamsters somewhere in the process. So, its use could be discovered because hamster material isn’t really a natural part of human blood. Right now, the more expensive brands of EPO have gotten rid off the hamsters, and use only human material. So, its illegal use by athletes cannot be discovered anymore. The latest figures I know, tell me that 80% of all the EPO produced isn’t used by kidney patients, sold to athletes.
You’re right, the difference in charge between native human Epo and recombinant Epo comes from differences in their glycosylation (specifically, different numbers of a charged sugar called sialic acid). It is quite common to find that recombinant human proteins made in non-human cells have somewhat different glycosylation patterns even though the protein (i.e. amino acid) sequences are identical. The “machinery” that glycosylates the protein is a little bit different in different species, and it makes slightly different oligosaccharide structures which are eventually attached to the protein. These structures are not controlled by the gene for Epo (or whatever), so they are characteristic of the host species, not the original human protein. So if the recombinant product is made in big tanks of, say, hamster cells, it will have a different “hamster-style” glycosylation pattern that will show up on isoelectric focusing or capillary electrophoresis. Some of the testing confusion seems to a
