Purification and Properties of a Periplasmic Protein

Publisher Website
Google Scholar
Abstract
Protein GLPT, a periplasmic protein previously recognized as closely related to the active transport of sn-glycerol-3-phosphate in E. coli, was isolated by the cold osmotic shock procedure. It was purified by Sephadex chromatography and isoelectric focusing. The purified protein does not exhibit any detectable binding activity toward sn-glycerol-3-phosphate. It has no activity as a glycerol phosphatase nor as a glycerol kinase. Polyacrylamide gel electrophoresis in the presence of dodecylsulfate of the protein subsequent to treatment in urea, boiling in dodecylsulfate and crosslinking indicates that it occurs as an oligomeric protein composed of 4 identical subunits of 40,000 MW. Membrane vesicles of wild-type strains that contain protein GLPT in whole cells loose it during vesicle preparation. However, they still exhibit high transport activity toward sn-glycerol-3-phosphate. Membrane vesicles prepared from glpT mutants that may or may not contain protein GLPT do not transport sn-glycerol-3-phosphate. Protein GLPT apparently does not participate in the energy-dependent active transport through the cytoplasmic membrane but could be involved in facilitating the diffusion of sn-glycerol-3-phosphate through the outer layers of E. coli.