HISTOCHEMICAL DEMONSTRATION OF FATTY ACID SYNTHESIZING ENZYMES

Abstract

A method for the histochemical demonstration of fatty acid synthesizing enzymes was deviced in mouse tissue, utilizing the characteristic nature of calcium salts of saturated fatty acid. Fresh frozen sections are incubated in a solution containing capryl-CoA, malonyl-CoA, NADPH, CaCl₂, glucose 6-phosphate, and other factors. Capryl-CoA, malonyl-CoA and NADPH undergo the enzymatic reaction and become higher fatty acids which are precipitated as insoluble calcium salts. Although calcium phosphate, which is formed by the decomposition of substrate and coenzyme, is also precipitated in sections, it is completely excluded by treatment with 0.1 M acetate buffer (pH 5.4) for 15 min, and calcium salts of higher fatty acids which remain stable are visualized by a method similar to the visualization procedures of Gomori's tween method for lipase. The reactions have been found in hepatic cells of mice throughout the entire lobules, sometimes also in periportal or centrilobular areas. Tubular epithelial cells of the kidney have also shown the reactions. A very week reaction is seen in heart muscle. The effect of inhibitor and fixation on enzyme activity, and changes in reaction in ethionine and carbon tetrachloride-induced fatty livers are discussed. These results are consistent with the biochemical data on fatty acid synthesizing enzymes.