Acetoacetate Formation in Liver

In 1944, Weinhouse et al. (1) reported that the incubation of carboxyllabeled octanoate with rat liver slices yielded acetoacetate in which the carboxyl and carbonyl carbons were equally labeled. Random condensation of 2-carbon units resulting from ,8 oxidation was therefore offered by these workers as a possible mechanism for the formation of acetoacetic acid from octanoate. The conversion of various carbons of octanoate to acetoacetate was also studied by Buchanan et al. (2), Crandall and Gurin (3), and Geyer et al. (4). Although the observations of these three groups of investigators still support the theory of /3 oxidation, the simple concept proposed by Weinhouse et al. does not completely explain their findings on the distribution of the isotope in the acetoacetate. Because of technical difficulties, nearly all of the previous investigations on acetoacetate formation have dealt with short chain fatty acids’ rather than with the naturally occurring, long chain acids. Some of the difficulties involved in the use of long chain fatty acids have been pointed out by Kennedy and Lehninger (6). Chain length did not exceed eight carbons in most of the earlier investigations. In the present investigation, we have studied the conversion, by liver slices, of various carbons of palmitic acid to acetoacetic acid. The carbons dealt with are the carboxyl, the 5th, and the 11th. The difficulties of bringing palmitic acid into contact with enzyme systems within the liver were overcome by intravenous injection of the labeled fat just before the rat was sacrificed.