Components of Phosphotransferases System - PTS

Components of Phosphotransferases System - PTS

	Components of Phosphotransferases System - PTS - The PTS comprises four proteins. Two of these are enzymes and two are substrates (HPr and Factor III). Enzyme I and HPr are general proteins, i.e. they are not sugar-specific. They are requited for the phosphorylation of all sugar substrates. The other two proteins are sugar specific, and form a protein duplex which is required for any given sugar. Some PTS sugars like glucose are translocated by two sugar-specific duplexes. Most sugars are, however, transported by only one system
Enzyme I:Has been isolated from Escherichia coli, Salmonella typhimurium and Staphylococcus aureus. It has a molecular weight of about 70,000. The active enzyme appears to be a dimer of MW 140,000. The E. coli and S. typhimurium proteins appear to be identical and can be substituted in vitro. The S. aureus protein is distinctly different, and shows no cross reactions with other enteric bacteria Enzyme II: E. coli and S. typhimurium the so-called Enzyme II appears to be a combination of two proteins (IIA and IIB) and phosphatidyl glycerol. Transfer of the phosphoryl group from phosphor HPr to the sugar substrates takes place by the help of sugar-specific proteins
A pair of sugar specific proteins (duplex) is required for phosphorylating a sugar. When tbe protein pair is firmly bound to the membrane, it is designated as IIA. and IIB. When one of the proteins of a pair is found in the cytoplasmic supernatant, it is called protein III and the membrane component is called IIB. IIB proteins act as sugar receptors or sugar binding proteins. Enzyme IIA is actually a family of enzymes, each specific to a different sugar. It can be separated into factors which specifically Phosphorylate glucose, or man nose or fructose
The Enzyme II complexes may function in facilitated diffusion, group translocation or active transport. There are reports that the complexes could catalyse facilitated diffusion, i.e. movement down the concentration gradient. Their role in group translocation, as in PTS sugars, is well established. Cleavage of the phospho Enzyme, II complex could provide the driving force for translocation of the solute against the electrochemical gradient (active transport). The sodium, potassium and calcium stimulated ATPases of higher organisms are examples of this type of transport

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