Methods-The methyl-terminal 2 carbons of fatty acids were obtained as acetic acid by a modification of the chromic acid oxidation described by Kuhn and Roth (18). Up to 20 mg of fatty acids were refluxed overnight in a solution of 5 ml of 5 N chromic acid and 1.2 ml of concentrated HzSOa. After the excess chromic acid was destroyed with hydrazine hydrate, the acetic acid was collected by steam distillation and isolated on Celite columns by the method of Swim and Utter (19) as modiied by Martin and Vagelos (20). Recovery of the methyl-terminal 2 carbons as acetic acid varied between 65 and 90%. The protein-bound radioactive product was precipitated from the reaction mixture by the addition of 0.1 volume of 1 N HCl. The precipitate was collected by centrifugation and washed with 0.2 N acetic acid (which contained 0.01 M 2-mercaptoethanol) until the wash showed negligible radioactivity(usually three washes). The precipitate was then redissolved in a solution which contained 0.01 M 2-mercaptoethanol and either 0.1 M triethanolamine-HCl, pH 7.5, or 0.1 M imidazole-HCl, pH 6.5. An aliquot of this solution was assayed for radioactivity in an end window gas flow counter or by liquid scintillation in Bray’s solution (21).

The reaction mixture for the formation of the protein-bound radioactive product under the conditions of Table I was subjected to fractionation by ammonium sulfate in the following way. The 3-minute incubation in a volume of 0.7 ml was terminated by the addition of 4.3 ml of a solution at 2’containing 0.1 M triethanolamine-HCI buffer, pH 7.5, and 0.01 M 2-mercaptoethanol to which had been added 2.38 g of ammonium sulfate. The solution, which was then 0.75 saturated with ammonium sulfate, was stirred for 10 minutes, and the precipitate which formed was collected by centrifugation. The supernatant solution, 0.75 saturated with ammonium sulfate, was brought to pH 1 by the addition of 1 N HCl, and the precipitate was collected by centrifugation. This treatment of the reaction mixture parallels the procedure by which Fraction A (precipitated at 0.75 saturated ammonium sulfate) is resolved from Enzyme II (precipitated from 0.75 saturated ammonium sulfate by acidification to pH 1)(8). The precipitate analogous to Fraction A was washed twice in a solution containing 0.1 M triethanolamine-HCl, pH 7.5, and 0.01 M 2-mercaptoethanol and which was 0.75 saturated in ammonium sulfate. The precipitate analogous to Enzyme II was washed three times in 0.2 N acetic acid which was 0.01 M with respect to 2-mercaptoethanol. Both precipitates were then resuspended in a solution which was 0.1 M imidazole-HCl,