X-His dipeptidase (bacteria)

Publisher Summary This chapter describes the structural chemistry and the biological aspects of X-His dipeptidase. Bacterial enzymes acting on X-His dipeptides were initially detected as carnosinases. The properties of dipeptidase PepD are similar to those of the so-called cytosol nonspecific dipeptidase, a broad-specificity metallopeptidase which, in addition to mammals and yeast, has also been detected in Mycobacterium, Streptococcus and E. coli B. Bacterial peptidases play essential roles in the utilization of substrates supplied in the medium and in the breakdown of intracellular proteins, especially under conditions of nutritional starvation. As camosinase apparently is not present among intestinal peptidases of animals, carnosine may occur extensively in the usual environment of enteric microorganisms. Enzymes with camosinase activity may be active in various gram-negative and gram-positive bacteria, but assigning them to the PepD type seems untimely because appropriate biochemical and genetic data are missing. The gene encoding the E. coli enzyme has been mapped and sequericed. Transcription is initiated with low efficiency at two adjacent promoters and increases 5-fold in response to phosphate limitation.