In the human body, as in all living cells, a paramount function of energy is to synthesize ATP from ADP and Pi. This is accomplished by a ubiquitous and complex enzyme, the ATP synthase. The synthase is embedded in the inner layer of the mitochondrion, whose principal function is to oxidize foodstuffs or synthesis of ATP. With increasing recognition of diseases resulting from mitochondrial dysfunction, it is important to learn how the normal mitochondrion functions. The long-term objective of this research is to gain understanding of the mechanism of ATP synthase. The synthase has 3 copies of catalytic beta subunits and 1,2,3, or more copies of other subunits. A binding change mechanism developed primarily by our laboratory suggests that conformational changes driven by proton translocation across the membrane serve to promote the competent binding of Pi and ADP and the release of tightly bound ADP. The three catalytic subunits in the static enzyme have strikingly different chemical and nucleotide binding properties. During catalysis they are proposed to function in a coordinated sequence so that at any one time each subunit is in a different conformation and positional arrangement with respect to other subunits. One objective of the present research is to find if such positional interchange occurs during catalysis. Methods for radioactive labeling of one subunit in a detectable conformation in the static enzyme are proposed, with the goal of finding if catalytic turnover causes subunit positional interchange. A second objective is to evaluate a new hypothesis that the synthase assumes different forms designed for ATP synthesis or hydrolysis depending on the orientation in the membrane of groups involved in proton translocation. A third objective is to find by use of 18O exchange measurements whether selected enzyme modifiers can uncouple subunit cooperativity and develop new reaction pathways. A final objective is to use 18O exchange and bound nucleotide measurements to learn why Mg2+ markedly inhibits the F1 ATPases and certain anions largely overcome the inhibition.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM011094-29
Application #
3268235
Study Section
Physical Biochemistry Study Section (PB)
Project Start
1975-05-01
Project End
1995-04-30
Budget Start
1991-05-01
Budget End
1992-04-30
Support Year
29
Fiscal Year
1991
Total Cost
Indirect Cost
Name
University of California Los Angeles
Department
Type
Schools of Arts and Sciences
DUNS #
119132785
City
Los Angeles
State
CA
Country
United States
Zip Code
90095
Murataliev, M B; Boyer, P D (1994) Interaction of mitochondrial F1-ATPase with trinitrophenyl derivatives of ATP and ADP. Participation of third catalytic site and role of Mg2+ in enzyme inactivation. J Biol Chem 269:15431-9
Boyer, P D (1993) The binding change mechanism for ATP synthase--some probabilities and possibilities. Biochim Biophys Acta 1140:215-50
Zhou, J M; Boyer, P D (1993) Evidence that energization of the chloroplast ATP synthase favors ATP formation at the tight binding catalytic site and increases the affinity for ADP at another catalytic site. J Biol Chem 268:1531-8
Zhou, J M; Boyer, P D (1992) MgADP and free Pi as the substrates and the Mg2+ requirement for photophosphorylation. Biochemistry 31:3166-71
Murataliev, M B; Boyer, P D (1992) The mechanism of stimulation of MgATPase activity of chloroplast F1-ATPase by non-catalytic adenine-nucleotide binding. Acceleration of the ATP-dependent release of inhibitory ADP from a catalytic site. Eur J Biochem 209:681-7
Murataliev, M B; Milgrom, Y M; Boyer, P D (1991) Characteristics of the combination of inhibitory Mg2+ and azide with the F1 ATPase from chloroplasts. Biochemistry 30:8305-10
Milgrom, Y M (1991) When beef-heart mitochondrial F1-ATPase is inhibited by inhibitor protein a nucleotide is trapped in one of the catalytic sites. Eur J Biochem 200:789-95
Berkich, D A; Williams, G D; Masiakos, P T et al. (1991) Rates of various reactions catalyzed by ATP synthase as related to the mechanism of ATP synthesis. J Biol Chem 266:123-9
Milgrom, Y M; Ehler, L L; Boyer, P D (1991) The characteristics and effect on catalysis of nucleotide binding to noncatalytic sites of chloroplast F1-ATPase. J Biol Chem 266:11551-8
Milgrom, Y M; Boyer, P D (1990) The ADP that binds tightly to nucleotide-depleted mitochondrial F1-ATPase and inhibits catalysis is bound at a catalytic site. Biochim Biophys Acta 1020:43-8

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