The requirements of the fatty acid oxidase complex of rat liver.

In an earlier paper it was shown that suspensions of the washed particulate portion of homogenized rat liver readily oxidized saturated fatty acids in the presence of adenosine triphosphate (ATP), Mgff, and inorganic phosphate (1). The information outlined in that paper allowed a quantitative analysis of the products of enzymatic fatty acid oxidation to be made (2), since such enzyme preparations were essentially free of endogenous respiratory activity. The oxidation of n-octanoate in these suspensions was found to proceed according to the equation, C,H&OOH + 302--, 2CH3COCH2COOH + 2Hz0. However, when the oxidation was allowed to take place in the presence of oxalacetate, the yield of acetoacetate diminished and citrate accumulated, implicating the Krebs tricarboxylic acid cycle in fatty acid oxidation in these enzyme preparations. The latter study also yielded some information as to certain features of the mechanism of fatty acid oxidation, supplementing the isotope studies of Weinhouse and his colleagues (3, 4) and Buchanan et al. (5). The gross mechanism of oxidation in the liver of the rat, at least, appears to involve the successive oxidative removal of 2-carbon units from the fatty acid. These units (which are not necessarily identical) may recondense with each other to form acetoacetate or they may react with oxalacetate to form tricarboxylic acids and thus enter into the Krebs cycle. With this broad outline of the gross mechanism of enzymatic fatty acid oxidation as a guide, attention in this laboratory was again turned to the study of the properties of the fatty acid oxidase complex with the end in mind of dissociating and characterizing separate reaction steps. In the course of attempts to isolate individual reactions of the highly integrated complex of enzymes by variations in the method of preparation, it was found that theenzyme system required several factors in addition to ATP and Mg++. In this paper experiments are described which led to recognition of some additional cofactors in enzymatic fatty acid oxidation and certain properties of the enzyme complex.