SUBCELLULAR-DISTRIBUTION AND PROPERTIES OF RABBIT LIVER AMINOACYL-TRANSFER RNA-SYNTHETASES UNDER MYOCARDIAL-ISCHEMIA

Subcellular distribution of aminoacyl-tRNA synthetase activities has b een studied in normal rabbit liver and under experimental myocardial i schemia (EMI). An increase in the activity of a number of aminoacyl-tR NA synthetases in postmitochondrial and postribosomal supernatants fro m rabbit liver has been determined 12 hr after EMI. Gel chromatography of the postribosomal supernatant on Sepharose 6B shows that aminoacyl -tRNA synthetase activities are distributed among the fractions with M (r) 1.82 x 10(6), 0.84 x 10(6) (high-M(r) aminoacyl-tRNA synthetase co mplexes) and 0.12-0.35 x 10(6). In the case of EMI aminoacyl-tRNA synt hetase, activities are partly redistributed from the 1.82 x 10(6) comp lex into the 0.84 x 10(6) complex. The catalytic properties of both fr ee and complex leucyl-tRNA synthetases have been compared. K(M) for al l the substrates are the values of the same order in norm and under EM I. A decrease in some aminoacyl-tRNA synthetase activities associated with polyribosomes has been observed 12 hr after EMI. The interaction of aminoacyl-tRNA synthetases with polyribosomes stimulates the cataly tic activity of some enzymes and protects them from heat inactivation in vitro. It is assumed that the changes in association of aminoacyl-t RNA synthetases with high-M(r) complexes and compartmentalization of t hese enzymes on polyribosomes may be related to the alteration of prot ein biosynthesis under myocardial ischemia.