Purification of a pregnenolone-binding protein in the soluble fraction of the guinea-pig adrenal cortex: differentiation from pregnenolone sulfotransferase.

A pregnenolone-binding protein has been purified from the 235,000 g soluble fraction of the guinea-pig adrenal cortex. The binding protein had an apparent molecular weight of 34,000 when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Since the functional status of the pregnenolone-binding protein is not known, a search for intrinsic catalytic activity was made. Because the binding protein is known to be a soluble protein consideration of a soluble enzyme activity was made which led to an investigation of the enzyme 3B-steroid sulfotransferase. Pregnenolone sulfotransferase activity, however, which was present in the soluble fraction, was found to be distinguishable from the pregnenolone-binding protein. Although the physicochemical distinction between these two factors was consistently noted with numerous experiments, it is speculated that there may exist a specific functional interaction between them. It was particularly interesting that both factors were concentrated in the inner cortical zone.