Hormonal and immunological aspects of the phylogeny of sex steroid binding plasma protein.

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Abstract
Sex steroid binding plasma protein (Sbp) in man and in monkeys [Papio papio, P. anubis, P. cynocephalus, P. hamadryas, Macaca mulatta, M. fascicularis, Ateles paniscus, Lagothrix lagotricha, Saimiri sciureus, Callithrix jacchus and Microcebus murinus] binds the androgens dihydrotestosterone and testosterone and the estrogen estradiol with high affinity (Kd .apprxeq. 0.5, 1 and 2 nM, respectively). Detailed studies of steroid binding specificity give the same results in all primates, except that in humans and chimpanzees estrone does not compete for dihydrotestosterone binding. In other mammals, Sbp of Artiodactyla and Lagomorpha have the same range of affinities for androgens, but they do not bind estradiol to any significant extent (Kd > 280 nM). The dog has an unusual Sbp (Kd for dihydrotestosterone, 7.1 nM; for estradiol, 125 nM), and rodents do not have a specific dihydrotestosterone-binding plasma protein. Gel filtration and immunoelectrophoretic experiments were performed with a monospecific antiserum against human Sbp. The results indicate variable cross-reactivities with Sbp of primates (from complete in chimpanzee and gorilla to weak in Prosimii). No cross-reaction was observed with specific androgen-binding plasma proteins of other species [including Xenopus laevis]. These results suggest the evolutionary emergence of bifunctional Sbp.