Progressive desialidation of human transferrin.

Transferrin is a serum glycoprotein which contains four sialic acid residues located at the end of two branched carbohydrate structures. The presence of these four acidic residues influences the electrophoretic mobility of the transferrin molecule. Alterations in the electrophoretic mobility of transferrin may be encountered in forensic science case work, particularly in association with postmortem samples. These altered transferrins usually appear in a highly stylized "ladder" banding pattern. To determine whether these altered transferrins are the result of sialic acid removal, serum samples of known transferrin type were treated with neuraminidase. These experiments support the hypothesis that the "ladder" banding pattern of transferrin observed in some case samples is due to the removal of sialic acid residues by bacterial or endogenous neuraminidase. These studies also demonstrate that partially desialidated transferrin variants cannot be clearly typed until the sialic acid is completely stripped from the transferrin molecule. Reliable typing of partially desialidated samples can be accomplished by treating these samples with neuraminidase.