Activation of adrenal sterol ester hydrolase by dibutyryl cAMP and protein kinase

Direct activation of adrenal Sterol Ester Hydrolase (EC 1.1.1.13) by dibutyryl cAMP, ATP and Mg⁺² has been demonstrated in adrenal homogenates from three species. Variability in the degree of activation was minimized by preincubation of the tissue homogenate for two hours prior to addition of the cofactors and subsequent enzyme assay. Although baseline sterol ester hydrolytic activity, independent of cofactors, was present in all subcellular fractions, the cAMP-dependent enzyme was primarily associated with the 105,000 × g soluble fraction of the cell. A requirement for protein kinase in the system was demonstrated with a partially-purified enzyme from bovine adrenal.