Evidence for histidyl and carboxy groups at the active site of the human placental Na+-H+ exchanger.

V. Ganapathy, D. F. Balkovetz, M. E. Ganapathy, V. B. Mahesh, Lawrence D Devoe, F. H. Leibach

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The Na+-H+ exchanger of the human placental brush-border membrane was inhibited by pretreatment of the membrane vesicles with a histidyl-group-specific reagent, diethyl pyrocarbonate and with a carboxy-group-specific reagent, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline. In both cases the inhibition was irreversible and non-competitive in nature. But, if the membrane vesicles were treated with these reagents in the presence of amiloride, cimetidine or clonidine, there was no inhibition. Since amiloride, cimetidine and clonidine all interact with the active site of the exchanger in a mutually exclusive manner, the findings provide evidence for the presence of essential histidyl and carboxy groups at or near the active site of the human placental Na+-H+ exchanger. This conclusion was further substantiated by the findings that Rose Bengal-catalysed photo-oxidation of histidine residues as well as covalent modification of carboxy residues with NN'-dicyclohexylcarbodi-imide irreversibly inhibited the Na+-H+ exchanger and that amiloride protected the exchanger from inhibition caused by NN'-dicyclohexylcarbodi-imide.

Original languageEnglish (US)
Pages (from-to)473-477
Number of pages5
JournalThe Biochemical journal
Issue number2
StatePublished - Jan 1 1987


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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