Activation of sterol ester hydrolase of bovine corpus luteum by N6,O2′-dibutyryl cyclic adenosine 3′∶5′-phosphate

The direct activation of sterol ester hydrolase (E.C. 3.1.1.13) in homogenates of bovine corpus luteum by N⁶O^2′·dibutyryl cyclic adenosine 3′∶5′-phosphate, (dibutyryl cAMP), adenosine triphosphate (ATP), and Mg²⁺ has been demonstrated. Variability in the extent of activation by the additions was minimized by homogenization of the tissue in 5 mM Mg²⁺. Baseline sterol ester hydrolase activity was primarily associated with the 105,000 × g soluble fraction, and significant activation of the enzyme preparation preincubated with dibutyryl cAMP, ATP and Mg²⁺ occurred within the first 15 min, prior to addition of substrate. A requirement for protein kinase in the system was demonstrated by blocking the cofactor-dependent enzyme activation with commercial protein kinase inhibitor.