EFFECT OF INHIBITOR BINDING TO BETA-SUBUNITS OF F(1)ATPASE ON ENZYME THERMOSTABILITY - A KINETIC AND FT-IR SPECTROSCOPIC ANALYSIS

FT-IR analysis shows that treatment of F(1)ATPase with the inhibitors DCCD and Nbf-Cl, in the presence of saturating concentrations of ADP a nd AMP-PNP and in the absence of Mg2+, does not modify the secondary s tructure of the enzyme, but significantly modifies its compactness and thermal stability, although to different extents, Nbf-Cl causes a sig nificant increase in stabilisation, in addition to that induced by nuc leotides, while DCCD is less effective in this regard, Determination b y HPLC of the exchange rate, in the absence of Mg2+, Of tightly bound nucleotides of F(1)ATPase treated with the two inhibitors shows that D CCD does not significantly affect the exchange rate of ADP with AMP-PN P and vice verse in catalytic and non-catalytic tight sites, while Nbf -Cl selectively reduces the enzyme's capacity to exchange ADP bound in the tight catalytic site. It is suggested that the effects of DCCD, u nlike those of Nbf-Cl, are closely related to the presence or absence of Mg2+. (C) 1998 Federation of European Biochemical Societies.