The acetate activating enzyme of beef heart.

Assay System-The assay system, previously described (1, 6, 7), is based on the conversion of acetyl CoA to citrate in the presence of malic dehydrogenase and condensing enzyme. The oxalacetate necessary for the condensation reaction is generated by the oxidation of malate in the presence of DPN, and the rate of DPN reduction is proportional to the concentration of AAE present, within the limits of the assay conditions (1). The specific activity is defined as micromoles of DPNH formed per mg. of protein per 15 minutes. A unit of enzyme activity is defined as that amount which leads to the formation of 1 ,uM of DPNH in 15 minutes. Preparation of Beef Heart Mitochondrial Particles-Fresh beef heart is freed from fat and connective tissue and diced. The subsequent steps are identical with those described previously for beef liver mitochondria (S), except that the acetone step is omitted and the particles are finally sus-