A phylogenetic study of the structural and functional characteristics of corticosteroid binding globulin in primates.

A monospecific antiserum against human corticosteroid binding globulin (hCBG) has been used to identify structural similarities between hCBG and CBG in the blood of other primates and representative species of different vertebrate classes. Double immunodiffusion analysis indicated that only CBG in Old World monkeys and apes cross-react with the hCBG antiserum. This was confirmed by a solid-phase radioimmunoassay for hCBG which also demonstrated that CBG in apes is immunologically identical to hCBG and that Old World monkey CBG comprises most, but not all, of the hCBG epitopes. The electrophoretic mobilities of human, gorilla and gibbon CBG were similar (RF 0.50-0.51), but differed from Old World monkey CBG (RF 0.44-0.49) and chimpanzee CBG (RF 0.47). Although serum/plasma cortisol binding capacities were similar in Old World primates, the dissociation half-times (t 1/2) of cortisol were higher from human and ape CBG (18-25 min) than from Old World monkey CBG (14-18 min). The steroid binding specificities of human and ape (CBG corticosterone greater than cortisol greater than progesterone greater than or equal to testosterone) were also different from those of Old World monkey CBG (corticosterone much greater than cortisol approximately equal to progesterone greater than testosterone). Lemur plasma cortisol binding capacity and CBG dissociation t 1/2 of cortisol were similar to hCBG, but its steroid binding specificity was different (cortisol greater than corticosterone greater than progesterone greater than or equal to testosterone) and it did not cross-react with the hCBG antiserum.(ABSTRACT TRUNCATED AT 250 WORDS)