Involved in the degradation of the side chains of C-24 branched-chain sterols. Catalyzes the ATP-dependent CoA thioesterification of the sterol 3-oxocholest-4-en-26-oate to yield 3-oxocholest-4-en-26-oyl-CoA. It can also use beta-sitosterol, campesterol and 3beta-hydroxy-5-cholesten-26-oate. (25S)-3-oxocholest-4-en-26-oate + ATP + CoA = (25S)-3-oxocholest-4-en-26-oyl-CoA + AMP + diphosphate Steroid metabolism; cholesterol metabolism. Cells lacking this gene are unable to degrade the side chain of C-24 branched sterols such as beta-sitosterol and campesterol. Belongs to the ATP-dependent AMP-binding enzyme family.