Acylaminoacid esterase mutants of Salmonella typhimurium

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Abstract
Salmonella typhimurium contains three electrophoretically separable enzyme activities that hydrolyze N-acetyl phenylalanine β-naphthyl ester (NAPNE). One of these enzymes is an endoprotease, protease I. Mutations at a locus apeA near purE lead to loss of this enzyme. We have found that N-acetyl leucine α-naphthyl ester (NALNE) is not hydrolyzed by protease I but is a good substrate for the other two activities. Using NALNE as a chromogenic substrate to screen colonies growing on agar, we have isolated mutants (apeB) that simultaneously lose both of the two other esterase activities. The chromosomal positions of apeB and nearby markers in the proC-purE region have been determined using both phage P1 and phage P22 mediated transduction. The observed order is proC thiC apeB apt apeA purE. Strains lacking all three activities (apeA apeB double mutants) have been constructed and have growth rates similar to wild-type strains.