Studies on ATP Citrate Lyase of Rat Liver

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Abstract
The mode of action of ATP citrate lyase [EC 4.1.3.8] was investigated using a single homogeneous preparation from rat liver. First, the enzyme was incubated with labelled citrate and after incubation the protein portion was isolated through a column of Sephadex G-50. It was found that an enzyme-citrate complex is formed in the presence of both ATP and Mg++. When this enzyme-citrate complex was isolated and then incubated with CoA, the formation of acetyl-CoA was demonstrated in the absence of added ATP. When 8-14C-ATP and γ-32P-ATP were separately incubated with the enzyme, radioactivity associated with protein was obtained only with γ-32P-ATP, but not with 8-14C-ATP. In accord with this, a rapid ATP-ADP exchange, but not an ATP-P1 exchange, was observed. These two reactions were solely dependent on the presence of Mg++. Therefore, the reaction involves the formation of an enzyme-phosphate complex.