Independent Regulation of Transport and Biosynthesis of Arginine in Escherichia coli K-12

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Abstract
From an arginine auxotrophic strain, a mutant was isolated which is able to utilize D-arginine as a source of L-arginine and shows a high sensitivity to inhibition of growth by canavanine. Transport studies revealed a 4 to 5-fold increased uptake of arginine and ornithine in cells from the mutant strain. The entry kinetics of arginine and ornithine evidenced elevated maximal influx values for the arginine- and ornithine-specific transport systems. A close parallel between arginine transport activity and arginine binding activity with 1 arginine-specific binding periplasmic protein in the mutant strongly suggests that such binding protein is a component of the arginine-specific permease. The affinity between arginine and the binder, isolated from the mutant cells, and the electrophoretic mobility of the protein, remain unchanged. The enhanced transport activity of arginine and ornithine with mutant cells is insensitive to repression by arginine or ornithine, but the biosynthesis of arginine-forming enzymes is normally repressible. When transport activity was examined in strains with mutations leading to derepression of arginine biosynthesis, the regulation of arginine transport was normal. Apparently, arginine transport and arginine biosynthesis in E. coli K-12 are not regulated in a concerted manner, although both systems may have common components.