JBC, Vol. 252, Issue 2, 464-470, Jan, 1977
A pregnenolone-binding protein in soluble fraction of guinea pig adrenal cortex
C. A. Strott
A pregnenolone-binding component has been detected in the soluble fraction
of the guinea pig adrenal cortex. Enzymatic degradation studies revealed
that the binding component was a protein. The binding was destroyed at 60
degrees but was not inhibited by sulfhydryl reactants. Pregnenolone was
bound optimally at pH 7 to 7.5 The equilibrium association constant at 0
degrees was 10(7) M-1. The pregnenolone-binding protein had an apparent
molecular weight of 58,000, as determined by gel filtration. With the
exception of pregnenolone sulfate, structurally similar steroids did not
interfere with pregnenolone binding. No such binding activity was detected
in the guinea pig liver and kidney. Serum contained pregnenolone-binding
activity which was distinguishable from the adrenal cytosol factor by a
variet of physicochemical means. The physiological importance of this
finding remains to be determined.