A STUDY OF LYSLY-RIBONUCLEIC ACID SYNTHETASE IN RELATION TO SUBSTRATE CONFORMATION

The substrate specificity of a purified lysyl-ribonucleic acid synthetase of Escherichia coli 9723 has been studied by determining the effects of a group of lysine analogs upon the enzymic transfer of lysine-C14 to soluble ribonucleic acid and lysine-dependent ATP-pyrophosphate exchange. At relatively high levels, 4-oxalysine, 2,6-diamino-4-hexynoic acid, and trans-4-dehydrolysine (but not cis-4-dehydrolysine) replace lysine in catalyzing the exchange reaction. Oxalysine, 2,6-diamlno-4-hexynolc acid, and trans-dehydrolysine inhibit enzymic transfer of lysine to soluble ribonucleic acid; the cis-isomer also inhibits lysine utilization but is less effective than the trans -isomer and other analogues. Thus the activation of lysine appears to require a conformation in which the 3 and 6 carbons are in a trans-like position, but binding with the enzyme can occur with other conformations.