Periplasmic protein related to the sn-glycerol-3-phosphate transport system of Escherichia coli

Abstract

Two-dimensional gel electrophoresis of shock fluids of E. coli K-12 revealed the presence of a periplasmic protein related to sn-glycerol-3-phosphate transport (GLPT) that is under the regulation of glpR, the regulatory gene of the glp regulon. Mutants selected for their resistance to phosphonomycin and defective in sn-glycerol-3-phosphate transport did not produce GLPT or produced it in reduced amounts. Other mutations exhibited no apparent effect on GLPT. Transductions of glpT+ nalA by phage P1 into these mutants and selection for growth on sn-glycerol-3-phosphate revealed a 50% cotransduction frequency to nalA. Reversion of mutants that did not produce GLPT to growth on sn-glycerol-3-phosphate resulted in strains that produce GLPT. This suggests a close relationship of GLPT to the glpT gene and to sn-glycerol-3-phosphate transport. Attempts to demonstrate binding activity of GLPT in crude shock fluid towards sn-glycerol-3-phosphate have failed so far. All shock fluids, independent of their GLPT content, exhibited an enzymatic activity that hydrolyzes, under the conditions of the binding assay, 30-60% of the sn-glycerol-3-phosphate to glycerol and Pi.