Inhibition of the Stearyl Coenzyme A Desaturase System by Sterculate

The mechanism of the inhibition in vitro of the microsomal stearyl-CoA desaturase system by sterculate has been investigated. Our data do not support the suggestions that this is mediated by the binding of thiol groups of enzyme proteins by the cyclopropene group and that this is competitive with substrate. Sterculate did inhibit the desaturase system in vitro but data suggest this to be nonspecific, stemming from the detergent nature of free fatty acid and hence of doubtful significance for metabolism in vitro. However, it was found that dietary (methyl) sterculate decreased the activity of the microsomal stearyl-CoA desaturase system. The mechanism of this action of sterculate remains obscure. A new procedure for the precise measurement of the microsomal stearyl-CoA desaturase system is described based on the permanganate-periodate oxidation of fatty acid methyl esters followed by the separation of monomethyl azelate-14C derived from oleate-1-14C from other fatty acid methyl esters with the use of a Florisil column. The utilization of rat liver microsomes for the enzymatic synthesis of stearyl-1-14C-CoA is also described.