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Index >> Membrane Transport >> Mechanism of Group Translocation by the Phosphotransferases - PTS

Mechanism of Group Translocation by the Phosphotransferases - PTS

	Mechanism of Group Translocation by the Phosphotransferases - PTS - The transfers of the phosphoryl group from PEP to the sugar take place in a sequential manner. The phosphoryl group is first transferred from PEP to Enzyme I. PEP + Enzyme I -->Pyruvate + Enzyme I ~ P The enzyme then transfers the phosphoryl group to an imidazole nitrogen atom (N-I) of a histidine residue in the heat-resistant protein (HPr) to form phospho ~ HPr, a true high energy compound.
Enzyme I ~ P + HPr --> Phospho ~ HPr + Enzyme I The overall transfer may be represented thus: Enzyme I PEP + HP------------>Phospho ~ HPr + Pyruvate Mg++ The phosphoryl group is next transferred to a sugar-specific protein, either protein UI (cytoplasmic) or IIA (membrane-bound)
Phospho ~ HPr + Protein III-->Protein III ~ P + HPr or Phospho ~ HPr + Protein IIA-->Protein IIA ~ P + HPr In the final step the phosphoryl group is transferred to the sugar molecule. This reaction is catalysed by protein IIB, which is also sugar-specific and is always a membrane bound component. Enzyme IIB
Protein III ~ P + Sugar-------------->Sugar-p + Protein III Enzyme IIB Protein IIA ~ P + Sugar-------------->Sugar-p + Protein II A The sugar is released inside the membrane in a modified form as a sugar phosphate

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