A 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DP) (the natural maturation-inducing hormone of salmonid fish) binding protein (DBP) was purified from rainbow trout plasma. It had an apparent molecular weight of 110 kDa on native PAGE and was composed of two subunits with molecular weights of 50 and 55 kDa on SDS-PAGE. Enzymatic digestion of sugar chains converted both subunits to a single peptide with a molecular weight of 42.5 kDa. Scatchard analysis of 17α,20β-DP binding to purified DBP showed the presence of a single binding site with a K(d) of 21 nM and B(max) of 5 nmol/mg of protein. The affinities of various steroids were estimated by the displacement of [3H]17α,20β-DP binding in the decreasing order of 17α,20β-DP, testosterone, 17α-hydroxyprogesterone, progesterone, estradiol-17β, 17α,20β,21-trihydroxy-4-pregnen-3-one, and cortisol. We conclude that DBP is a sex-hormone binding globulin in rainbow trout.
All Science Journal Classification (ASJC) codes
- Animal Science and Zoology