The utilization of butyric acid for the synthesis of cholesterol and fatty acids.

It has previously been found in this laboratory that in the biological synthesis of cholesterol the terminal methyl carbons of isovaleric acid are much more efficient carbon sources than the carboxyl carbons of the same compound and are also more effective sterol precursors than the carbon atoms of acetic acid (1). One explanation offered for these findings was that isovalerate is broken down to two types of Cz units and that one of these is more active in sterol synthesis than the other. In order to test this interpretation and to determine whether a similar result would be obtained with a straight chain fatty acid, the conversion of butyric acid to various metabolic products was studied. The test substance was doubly labeled butyrate, prepared by mixing butyrate-1-P and butyrate-3-P. Isotope concentrations were determined in acetoacetate formed in rat liver slices, and in cholesterol and the fatty acids isolated from rats which had been fed labeled butyrate.