Proline excretion in Escherichia coli: A comparison of an argD + strain and a proline-excreting argD ? derivative

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Abstract
In an attempt to deduce the physiological basis of proline excretion in argD− strains of Escherichia coli K12, several properties of an argD+ (nonexcreting) and an argD− (excreting) derivative were compared. No difference was found in the transport or in the utilization of either proline or its immediate precursor, Δ1-pyrroline-5-carboxylate (PCA). Furthermore, no differences were found in the physical or kinetic properties of partially purified preparations of the enzyme mediating the final step in proline biosynthesis, PCA reductase. The specific activity of PCA reductase was, however, consistently higher in crude extracts prepared from the argD− mutant.