PROTEIN BIOSYNTHESIS BY A CELL-FREE BACTERIAL SYSTEM. II. FURTHER STUDIES ON THE AMINO ACID INCORPORATION ENZYME

Abstract

The amino acid incorporation enzyme is present in the supernatant fraction obtained from rat liver homogenates and in the precipitate obtained by acidification of this fraction to pH 5.2 (pH 5 enzymes). Highly purified amino acid incorporation enzyme from Alcaligenes faecalis completely replaces the pH 5 enzymes in stimulating the incorporation of C -leucine into protein of rat liver microsomes. These observations show that the amino acid incorporation enzyme is involved in protein biosynthesis in both mammalian and bacterial cells. Highly purified preparations of the A. faecalis incorporation enzyme catalyze a rapid Mg++-dependent excnange of radioactive aderiosine diphosphate with adenosine triphosphate an activity which appears to be related to their amino acid incorporation activity. This finding may be of significance, since glutathione synthetase, which catalyzes the synthesis of a typical peptide, brings about a similar exchange.