Mechanism of ATP hydrolysis by beef heart mitochondrial ATPase. Rate enhancements resulting from cooperative interactions between multiple catalytic sites.
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Adenosine Triphosphatases↗
Biomedical subjects
C Grubmeyer
Publications and source records attributed to C Grubmeyer.
The presence of two hydrolytic sites on beef heart mitochondrial adenosine triphosphatase.
The ribose-modified nucleotides 2',3'-O-(2,4,6-trinitrophenyl) adenosine 5'-triphosphate (TNP-ATP) and TNP-ADP were used to probe the catalytic sites on soluble beef heart mitochondrial adenosine triphosphatase (F1). Both compounds were potent competitive inhibitors of ATP hydrolysis catalyzed by F1, Ki = 5.5 and 10 nM, respectively, and by submitochondrial particles, Ki (TNP-ATP) = 21 nM. Both compounds also were potent competitive inhibitors of ATP synthesis during oxidative phosphorylation (Ki = 1300 nM). Both analogs inhibited the 32Pi-ATP exchange reaction and the ATP-dependent reduction of NAD+ by succinate, catalyzed by submitochondrial particles. TNP-ATP and TNP-ADP were bound by F1. The presence of two binding sites on the enzyme for TNP-adenine nucleotides was determined by titrations of difference absorbance spectra, of the increase in fluorescence of the analog which occurred upon interaction with protein, and by titrations with the centrifuge column method using 32P-labeled TNP-adenine nucleotides. The first binding site bound the analogs with an affinity too high to be measured. The Kd for analog binding by the second site was 20 to 80 nM. In the presence of Mg2+, the 2 sites were filled with the TNP-ATP at a rate too rapid to be resolved by the procedure used. TNP-[gamma-32P]ATP was hydrolyzed by F1, Km = 0.2 microM, Vmax = 1.1 mol of 32Pi formed/mol of F1/s. It was shown, using the isotope trap technique as well as the inhibitor efrapeptin, that the 2 binding sites for TNP-ATP on F1 are hydrolytic sites.
Adenine Nucleotides↗
Cooperatively between catalytic sites in the mechanism of action of beef heart mitochondrial adenosine triphosphatase.
Occupancy of only one of two hydrolytic sites on beef heart mitochondrial ATPase (F1) by the radioactive ATP analog, 2',3'-O-(2,4,6-trinitrophenyl) adenosine 5'-[gamma-32P]-triphosphate (TNP-[gamma-32P]ATP) is associated with a low rate of hydrolysis of the substrate even under conditions otherwise favoring catalysis. Addition of excess nonradioactive TNP-ATP, in concentrations sufficient to fill catalytic Site 2 on the enzyme (Grubmeyer, C., and Penefsky, H. S. (1981) J. Biol. Chem. 256, 3718-3727), accelerates the rate of hydrolysis of the radioactive substrate 15- to 20-fold. Since the excess nonradioactive substrate serves as an effective isotope trap, the involvement of medium TNP-[gamma-32P]-ATP as an intermediate is ruled out. These observations constitute direct evidence for catalytic cooperativity between active sites on F1. It is proposed that the use of high binding affinity substrates or substrate analogs, combined with the isotope trap technique, offers a new approach to the detection and study of catalytic site cooperativity in enzymes. The hydrolyzable nucleotides GTP, ITP, and ATP are excellent promoters of the hydrolysis of previously bound TNP-[gamma-32P]ATP whereas addition of nonhydrolyzable nucleotides such as TNP-ADP, ADP, and adenylyl imidodiphosphate result in a lower rate and extent of hydrolysis. AMP is without effect. Studies of the hydrolysis of [gamma-32P]ATP and TNP-[gamma-32P]ITP, under appropriate conditions, also provide evidence consistent with promoted catalysis. Based upon these findings, a model is presented for the mechanism of action of F1 in which site-site cooperativity reflects promoter-dependent hydrolysis of bound substrate.
Adenosine Triphosphatases↗
The stereochemical course of phosphoric residue transfer catalyzed by beef heart mitochondrial ATPase.
The stereochemical course of phosphoric residue transfer has been determined for beef heart mitochondrial ATPase. When aden 5'-(3-thiotriphosphate), stereospecifically labeled with 18O in the gamma position, was hydrolyzed in [17O]water in the presence of the ATPase, the product inorganic [16O, 17O, 18O]thiophosphate was chiral. The configuration of the product showed that the hydrolysis had proceeded with inversion at the gamma-phosphorus atom. This result suggests that there is a direct, in-line transfer of the phosphoric residue between ADP and water and that there is no phosphoenzyme intermediate.
Adenosine Triphosphatases↗
ATPase Activity of Pea Cotyledon Submitochondrial Particles: ACTIVATION, SUBSTRATE SPECIFICITY, AND ANION EFFECTS.
Submitochondrial particles freshly prepared by sonication from pea cotyledon mitochondria showed low ATPase activity. Activity increased 20-fold on exposure to trypsin. The pea cotyledon submitochondrial particle ATPase was also activated by "aging" in vitro. At pH 7.0 addition of 1 millimolar ATP prevented the activation. ATPase of freshly prepared pea cotyledon submitochondrial particles had a substrate specificity similar to that of the soluble ATPase from pea cotyledon mitochondria, with GTPase > ATPase. "Aged" or trypsin-treated particles showed equal activity with the two substrates. NaCl and NaHCO(3), which stimulate the ATPase but not the GTPase activity of the soluble pea enzyme, were stimulatory to both the ATPase and GTPase activities of freshly prepared submitochondrial particles. However, they were stimulatory only to the ATPase activity of trypsin-treated or "aged" submitochondrial particles. In contrast, the ATPase activity of rat liver submitochondrial particles was stimulated by HCO(3) (-), but inhibited by Cl(-), indicating that Cl(-) stimulation is a distinguishing property of the pea mitochondrial ATPase complex.
Journal Article↗
Oxidative phosphorylation in pea cotyledon submitochondrial particles.
Mitochondria and submitochondrial particles (SMP) from pea cotyledons were shown to catalyze oxidative phosphorylation as measured by (32)Pi uptake into phosphate esters. ATP synthesis was sensitive to the electron transport inhibitor KCN, the uncoupler carbonyl cyanide m-chlorophenylhydrazone, and the coupling factor inhibitor oligomycin. Experiments with the adenine nucleotide translocator inhibitor atractyloside indicated the SMP were inside-out. Mersalyl completely inhibited ATP synthesis by SMP, and a separate experiment indicated that mersalyl has a direct effect on the ATPase complex. The kinetics of ATP synthesis indicated a high affinity for phosphate (K(m) = 0.18 millimolar). ADP kinetics gave a biphasic curve with K(m) values of about 4.8 and 160 micromolar. O(2) uptake and ATP synthesis had a pH maximum of 7.6 while the ratio of micromoles phosphate esterified to microatoms O(2) taken up was highest at pH 7.2. Sodium chloride inhibited both ATP synthesis and O(2) uptake but stimulated the ATPase reaction. The SMP also catalyzed a slow ATP-phosphate exchange reaction.
Journal Article↗
Oligomycin-sensitive ATPase of Submitochondrial Particles from Corn.
To test the hypothesis (Plant Physiology 59: 155-157) that monocotyledons contain a unique oligomycin-insensitive ATPase, we prepared submitochondrial particles and a soluble fraction from sonicated corn mitochondria (Zea mays L. cv. Earliking). Although the ATPase activity of the whole sonicate was relatively insensitive to oligomycin, the corn submitochondrial particles possessed an ATPase activity that was nearly completely inhibited by oligomycin, and was activated by trypsin. This ATPase is similar to that from other sources (plants, animals, and microorganisms). The soluble fraction also contained an active ATPase, which was inhibited by azide and stimulated by sodium chloride and trypsin. The soluble fraction differed from other F(1)-ATPases in that it was cold-stable.
Journal Article↗
Partial characterization of a soluble ATPase from pea cotyledon mitochondria.
A partially purified soluble ATPase (ATP phosphohydrolase, EC 3.6.1.3) from pea cotyledon mitochondria was characterized. Inhibition patterns with azide, NaF, and cold, and a stimulation by 2,4-dinitrophenol were typical of F1-ATPases from mammalian mitochondria. The enzyme hydrolysed GTP, ITP, and ATP, but not CTP, UTP, ADP, or IDP. ATPase and ITPase activities were strongly inhibited by ADP and to a lesser extent by IDP. Distinctive properties of the pea mitochondrial enzyme were activation by high concentrations of CaCl2 and stimulation by NaCl.
Adenosine Diphosphate↗