The functional size of acyl-coenzyme A (CoA):cholesterol acyltransferase and acyl-CoA hydrolase as determined by radiation inactivation

Frozen rat liver microsomes and rough endoplasmic reticulum were irradiated with high energy electrons. The surviving enzymatic activity of acyl-CoA:cholesterol acyltransferase and activity for esterification of 25-hydroxycholesterol decreased as a simple exponential function of radiation exposure, leading to a target size of 170-180 kDa. The loss of acyl-CoA hydrolase activity with a radiation dose was complex and resolved as a 45-kDa enzyme associated with a large inhibitor. It is interpreted that acyl-CoA hydrolase is the acyl-CoA-binding component and the inhibitor is the cholesterol-binding component of acyl-CoA:cholesterol acyltransferase.