The Transport of Carbohydrates by a Bacterial Phosphotransferase System

Abstract

The components and properties of a phosphoenolpyruvate: glucose phosphotransferase system are reviewed, along with the evidence implicating this system in sugar transport across bacterial membranes. Some possible physiological implications of sugar transport mediated by the phosphotransferase system are also considered. This paper is concerned with a bacterial phosphotransferase system; its properties, and evidence indicating it to be responsible for sugar transport in bacterial cells will be briefly reviewed, and some speculations will be offered concerning the physiological implications of sugar transport via this system.The discovery of the phosphotransferase system resulted from our longstanding interest in the biosynthesis of carbohydrate containing macromolecules (1). The 9-carbon sugar acid, sialic acid, is a frequent component of these macromolecules, and enzymatic degradation of one of the sialic acids (N-acetylneuraminic acid) was found to give pyruvate and N-acetyl-Dmannosamine (2). Studies on the metabolism of the latter sugar led to the discovery of a specific kinase that catalyzes the reaction shown in Fig. 1 ; this kinase is widely distributed in animal tissues (3). Since certain bacterial cells synthesize polymers of N-acetylneuraminic acid, or can metabolize N-acetyl-D-mannosamine, extracts of these cells were examined for the kinase. The sugar was not phosphorylated by the reaction shown in Fig. 1, but it was phosphorylated when phosphoenolpyruvate (PEP) was substituted for ATP. The bacterial system, designated PEP:glycose phosphotransferase system, or simply phosphotransferase system, was found to catalyze the reaction shown in Fig. 2 (4, 5).

Pathway of fructose utilization by Escherichia coli

“…This was found to be so: whereas frozen and thawed suspensions of the wild-type KL 16, which had been grown on glycerol plus fructose, catalysed the PEP-dependent formation of 2 1 nmoles of fructose-1 -phosphate from fructose min-' mg dry wt-' of cells, suspensions of KL 16-2 1, similarly grown, phosphorylated less than 1 nmole of fructose under these conditions. Secondly, the phosphorylation reaction (1) has been shown to be necessarily associated with uptake of hexoses by E. coli (for review, see [20] ). It would thus be expected that a mutant lacking enzyme II activity would be impaired in the uptake of labelled fructose.…”

Understanding phospholipid function: Why are there so many lipids?

“…Gene's group correctly suggested that the M protein carried out both energy-independent equilibration of substrate across the cell membrane as well as energy-dependent accumulation of substrate without modification of the substrate (12). This was in stark contrast to the phosphotransferase-dependent systems studied by Saul Roseman (13), which used metabolic energy to modify the substrate, resulting in accumulation. These differences in mechanism provided colorful debates at Gordon Research Conferences for several years between Saul, Gene, and H. Ronald Kaback as to the mechanism by which LacY transports substrate.…”

Close Linkage between a Galactose Binding Protein and the β‐Methylgalactoside Permease in Escherichia coli

“…Thus, what are the other components necessary for the function of the MeGal-permease Z The phosphotransferase system described by Kundig et al [24] has certainly to be discussed in this respect. Roseman [25] suggested that a variety of sugars including galactose are transported by the phosphoenol-pyruvate dependent phosphotrans ferase system. According to this theory, the specificity of the MeGal-permease resides in a specific Enzyme I1 complex.…”