Metabolism of homologous and heterologous serum proteins in garter snakes (Thamnophis ordinoides).

The half life (T1/2) of serum immunoglobulin (Ig) and albumin from snakes and mammals were determined in both garter snakes (Thamnophis ordinoides) and mice (Mus musculus). Metabolism of serum proteins in snakes was similar to mammalian protein metabolism in that homologous serum albumin had shorter T1/2 (16 days) than IgG (38 days). Also, reptilian and mammalian serum proteins had a relatively longer T1/2 when injected into closely related species. Thus mammalian serum Ig (rabbit gamma globulin (RGG)) had a shorter T1/2 (6.3 days) in snake than did homologous snake IgG (38 days), whereas in mice, RGG had a longer T1/2 (3.8 days) than snake Ig (0.9 days). Differences between metabolism of homologous and heterologous albumins were apparent only in snakes in which the T1/2 of homologous albumin was approximately 8-fold greater than mammalian albumin. These results indicate that metabolism of both Ig and albumin in snakes is regulated by specific receptors whereas albumin receptors have been difficult to demonstrate in mammals. The results of this study suggest that one of the factors determining the metabolism of a protein is its foreignness to the host perhaps because of receptor cross reactions.