title: lac permease of Escherichia coli: histidine-322 and glutamic acid-325 may be components of a charge-relay system.
abstract: When Glu-325 in the lac permease of Escherichia coli is replaced with Ala, lactose/H+ symport is abolished. Thus, the altered permease catalyzes neither uphill lactose accumulation nor efflux. Remarkably, however, permease with Ala-325 catalyzes exchange and counterflow at completely normal rates. Taken together with the results presented in the accompanying paper [Püttner, I. B., Sarkar, H. K., Poonian, M. S., & Kaback, H. R. (1986) Biochemistry (preceding paper in this issue)], the findings suggest that the His-322 and Glu-325 may be components of a charge-relay system that plays an important role in the coupled translocation of lactose and H+.
mesh_terms: D001665:Binding Sites; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins; D005971:Glutamates; D018698:Glutamic Acid; D006639:Histidine; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D009154:Mutation; D027981:Symporters
chemical_list: D029968:Escherichia coli Proteins; D005971:Glutamates; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; D018698:Glutamic Acid; D006639:Histidine; C021499:lactose permease