Lowered temperature or binding of pyrophosphate to sites for noncatalytic nucleotides modulates the ATPase activity of the beef heart mitochondrial F1-ATPase by decreasing the affinity of a catalytic site for inhibitory MgADP
Jault, J.M.; Paik, S.R.; Grodsky, N.B.; Allison, W.S.
Biochemistry 33(50): 14979-14985
ISSN/ISBN: 0006-2960 PMID: 7999754 DOI: 10.1021/bi00254a005
Lineweaver-Burk plots for ATP hydrolysis catalyzed by bovine heart mitochondrial F1-ATPase (MF1) at 30 degrees C are biphasic, whereas they are linear at 15 degrees C. The rate of inactivation of the enzyme at 23 degrees C by 5'-[(p-fluorosulfonyl)benzoyl]adenosine (FSBA), which derivatizes noncatalytic nucleotide binding sites, is about 4 times faster when loss of activity is monitored at 15 degrees C as opposed to 30 degrees C. This suggests that maximal loss of ATPase monitored at 15 degrees C is observed when a single noncatalytic site is derivatized, whereas maximal inactivation at 30 degrees C requires modification of three noncatalytic sites. Prior incubation of MF1 depleted of endogenous nucleotides (nd-MF1) with pyrophosphate (PPi) stimulates ATPase activity 2-fold when assayed at 30 degrees C and pH 8.0. This stimulation correlates with binding of [32P]PPi to the second and third binding sites for PPi to be filled. Prior binding of PPi to nd-MF1 increases the rate of inactivation of the enzyme by FSBA at 23 degrees C about 4-fold when loss of activity is monitored at 30 degrees C and pH 8.0, whereas it does not affect the rate of inactivation when loss of ATPase is monitored at 15 degrees C or loss of ITPase is monitored at 30 degrees C. This indicates that the accelerated rate of inactivation induced by PPi when assays are conducted at 30 degrees C is not due to an increased rate of derivatization of noncatalytic sites. After 85% inactivation with FSBA, nd-MF1 retains the capacity to bind 2.8 mol of [32P]PPi per mole.