Promod R Pratap

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The Na+/K(+)-ATPase couples the hydrolysis of ATP to the transport of Na+ and K+ via a phosphorylated intermediate and conformational changes. In order to identify these conformational changes, we have probed the sequence of steps from EP(3Na+ in) to EP + 3Na+ out with three fluorescent probes (IAF: 5-iodoacetamidofluorescein; BIPM:(More)
The Na+/K(+)-ATPase functions in cells to couple energy from the hydrolysis of ATP to the transport Na+ out and K+ in. The fluorescent probe IAF (iodoacetamidofluorescein) covalently binds to this enzyme, reporting conformational changes without inhibiting enzyme activity. This paper describes experiments using dog kidney enzyme labeled with IAF to examine(More)
The light-growth responses of Phycomyces behavioral mutants, defective in genes madB, madC, and madH, were studied with the sum-of-sinusoids method of system identification. Modified phototropic action spectra of these mutants have indicated that they have altered photoreceptors (P. Galland and E.D. Lipson, 1985, Photochem. Photobiol. 41:331). In the two(More)
This series of papers addresses the mechanism by which certain impermeant oxonol dyes respond to membranepotential changes, denoted ΔE m . Hemispherical oxidized cholesterol bilayer membranes provided a controlled model membrane system for determining the dependence of the light absorption signal from the dye on parameters such as the wavelength and(More)
Conformational changes between E1 and E2 enzyme forms of a dog kidney Na+/K(+)-ATPase preparation labeled with 5-iodoacetamidofluorescein were followed with a stopped-flow fluorimeter, in terms of the rate constant, kobs, and the steady-state magnitude, % delta F of fluorescence change. On rapid mixing of enzyme plus Mg2+ plus Na+ with saturating (0.5 mM)(More)
We have measured potential-dependent changes in the absorption of light by oxidized cholesterol bilayer lipid membranes in the presence of impermeant oxonol dyes. The magnitude of the absorption signal increased linearly with the size of potential steps over a range of 500 mV. The signal also increased when the offset voltage of the pulse train was(More)
Net K and Cl effluxes induced by valinomycin or by gramicidin have been determined directly at varied external K, denoted by [K]o, in the presence and absence of the anion transport inhibitors DIDS (4,4'-diiso-thiocyano-2,2'-disulfonic acid stilbene), and its less potent analogue SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid). The results(More)
Optical potentiometric indicators have been used to monitor the transmembrane electrical potential (Em) of many cells and organelles. A better understanding of the mechanisms of dye response is needed for the design of dyes with improved responses and for unambiguous interpretation of experimental results. This paper describes the responses to delta Em of(More)
Adding 15 mM free Mg2+ decreased Vmax of the Na+/K(+)-ATPase reaction. Mg2+ also decreased the K0.5 for K+ activation, as a mixed inhibitor, but the increased inhibition at higher K+ concentrations diminished as the Na+ concentration was raised. Inhibition was greater with Rb+ but less with Li+ when these cations substituted for K+ at pH 7.5, while at pH(More)