JBC, Vol. 251, Issue 21, 6705-6710, Nov, 1976
Effect of inosine 5' -(beta, gamma-imido) triphosphate and other nucleotides on beef heart mitochondrial ATPase
S. M. Schuster, R. J. Gertschen and H. A. Lardy
The effects of various substrates and alternative substrates on the
hydrolytic activity of beef heart mitochondrial ATPase was examined. It was
found that ATP or ADP, ITP hydrolysis showed positive cooperativity. IDP
inhibited ITP hydrolysis and caused positive cooperativity. When ITP was
present during an ATP hydrolysis assay, the rate of ATP hydrolysis was
stimulated. IDP had no effect on ATP hydrolysis rates. A nonhydrolyzable
ITP analog, inosine 5'-(beta, gamma-imido)triphosphate (IMP-P(NH)P), was
synthesized and purified. It was found to be a potent competitive inhibitor
of ITP and GTP hydrolytic activity. However, this beta-gamma-imido-bridged
ITP analog was found to change the ITP and GTP hydrolysis kinetics from
linear to positively cooperative. This compound inhibited ATP hydrolysis at
substrate concentrations of 100 muM and lower, and stimulated ATP
hydrolysis at substrate concentrations between 100 muM and 2 mM. IMP-P(NH)P
had no effect on ATP hydrolysis when the substrate concentration was above
2 mM. In the presence of the activating anion, bicarbonate, IMP-P(NH)P
inhibited ATP hydrolysis competitively, and induced positive cooperativity.
IMP-P(NH)P had no effect on the ATP equilibrium Pi exchange, the ITP
equilibrium Pi exchange, or ATP synthesis catalyzed by beef heart
submitochondrial particles.
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