Interaction of Escherichia coli adenosine triphosphatase with aurovertin and citreoviridin: inhibition and fluorescence studies

Abstract

Aurovertins B and D inhibited the adenosine triphosphatase (ATPase) activity of soluble Escherichia coli coupling factor ATPase (BF1) isolated from wile-type E. coli K-12. Half inhibition was obtained with 2 microns aurovertin B and 0.9 microns aurovertin D. Aurovertins B and D had no inhibitory effect on BF1 isolated from the aurovertin-resistant E. coli mutant MA12. Acetylation or saponification of aurovertin D yielded a derivative which was devoid of inhibitory effect on BF1. Citreoviridin also inhibited wild-type BF1 but with much less efficiency (half inhibition at 60 microns) than aurovertin. Citreoviridin had no effect on the aurovertin-resistant BF1. The fluorescence intensity of aurovertins B and D was markedly enhanced upon addition to purified BF1. There was no enhancement of fluorescence when the aurovertins were added to BF1 isolated from the aurovertin-resistant mutant. The fluorescence of the aurovertin-BF1 complex was enhanced by adenosine 5'-diphosphate and by low concentrations of adenosine 5'-triphosphate. The adenosine 5'-diphosphate-enhanced fluorescence of the aurovertin-BF1 complex was quenched by high concentrations of adenosine 5'-triphosphate or by MG2+. Aurovertin bound selectively to the beta subunit of BF1 isolated from wile-type cells. By complementation assays in vitro, using a reconstituted system made of subunits isolated from wild-type and aurovertin-resistant BF1, it was shown that the altered peptide in aurovertin-resistant BF1 was the beta subunit.