Some characteristics of the enzymic carboxyl activation of methionine

Abstract

Rat-liver homogenate prepared in 0.25 M sucrose was separated into particulate and supernatant fractions. The presence of an enzyme activating the carboxyl group of methionine could be demonstrated in the supernatant, but no such activity was found in a 0.05 M KC1 extract of the particulate fraction. The enzyme was inhibited 20-30% by yeast ribonucleic acid, and by an enzymic hydrolysate of ribonucleic acid, but not by thymus deoxyribo-nucleic acid. Glycylmethionine and alanyl-methionine were activated by the enzyme preparation, but alanylmethionine activation was lower than that of methionine or glycylmethionine. Inhibitors of protein synthesis (12 mM ethionine, ribonuclease, protamine, 25 mM sodium fluoride, 25 mM sodium azide, 25 mM dinitrophenol) failed to inhibit the enzyme activity.