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A G Hunt

Publications and source records attributed to A G Hunt.

41 records · Page 3Linked to original sources
PubMed1983

Involvement of histidine and tryptophan residues of glutamine binding protein in the interaction with membrane-bound components of the glutamine transport system of Escherichia coli.

We treated the glutamine binding protein with diethyl pyrocarbonate (DEPC) and N-bromosuccinimide (NBS) to modify respectively the sole histidine and tryptophan residues and examined the effect of these modifications on the ability of the binding protein to bind glutamine as well as the ability to restore glutamine transport in membrane vesicles of Escherichia coli. Under the conditions used, both DEPC and NBS markedly inhibited the ability to restore glutamine transport in vesicles without any significant effect on glutamine binding. Moreover, saturating quantities of glutamine had no protective effect on the inactivation of the binding protein by DEPC or NBS. Fluorometric measurement and amino acid analysis indicate that the inactivation of the binding protein in restoring vesicle transport by NBS can be attributed to the oxidation of a single tryptophan residue. Similar analysis and the inability of hydroxylamine to reverse the effect of DEPC indicate that the effects of DEPC can probably be attributed to alterations of the sole histidine and/or one or more lysine residues of the binding protein. We conclude that the glutamine binding protein possesses at least two largely nonoverlapping functional domains, one responsible for glutamine binding and the other for the interaction with the other components of the glutamine transport system.

Biological Transport, Active↗
PubMed1981

The reconstitution of binding protein-dependent active transport of glutamine in isolated membrane vesicles from Escherichia coli.

The reconstitution of binding protein-dependent glutamine transport in isolated membrane vesicles from Escherichia coli is described. The reconstituted glutamine transport is shown to be energy-dependent and does not involve the metabolism of glutamine or the trapping of liganded binding protein with the vesicles. The preparation of vesicles capable of transporting glutamine in a binding protein-dependent manner required the incorporation of NAD into vesicles and the use of a binding protein point mutant as the source of the vesicles.

Biological Transport, Active↗
PubMed1979

Requirements of acetyl phosphate for the binding protein-dependent transport systems in Escherichia coli.

In Escherichia coli, acetyl phosphate can be formed from acetyl-CoA via the phosphotransacetylase (phosphate acetyltransferase; acetyl-CoA:orthophosphate acetyltransferase, EC 2.3.1.8) reaction and from acetate (plus ATP) via the acetate kinase (ATP:acetate phosphotransferase, EC 2.7.2.1) reaction. By restricting acetyl phosphate formation to the phosphotransacetylase reaction alone, through the use of metabolic inhibitors, we were able to show that, with pyruvate as a source of energy, mutants defective in phosphotransacetylase are unable to transport glutamine, histidine, and methionine. However, with the same energy source, mutants defective in acetate kinase are normal in the transport of these amino acids. The inability of the phosphotransacetylase mutants to transport is due to their presumed inability to form acetyl phosphate, because pyruvate is found to be metabolized to acetyl-CoA in these mutants. Thus acetyl phosphate has been implicated in active transport. Evidence is also presented that neither the protonmotive force nor the ecf gene product is required for the shock-sensitive transport systems.

Acetates↗