The proposed research focuses on the mechanisms of mitochondrial ATPase reactivation and inhibitor protein release which operates during the re-energization of intact mitochondria and submitochondrial particles (SMP) isolated from ischemic cardiac muscle.
The first aim of the planned work is to establish conditions which will differentiate clearly between two putative, independently regulated sites of ATPase inhibitor-enzyme interaction, a fast-releasing regulatory site which is controlled primarily by the trans-membrane pH gradient, and a slow- releasing binding site and to show how the slow-releasing binding site is regulated.
Our second aim i s to examine possible conformational changes in the inhibitor protein (using a fluorescence probe covalently bound to the inhibitor) which may accompany both its rapid release from the regulatory site and its slow release from the binding site during the re-energization of SMP.
Our third aim i s to quantitate further the importance of the reversible inhibition of the mitochondrial ATPase in the control of tissue ATP depletion in situ in ischemic heart muscle. Data recently acquired in this laboratory suggest the existence of two distinct kinds of interaction between ATPase inhibitor protein and enzyme. One is a rapid, regulatory interaction which affects enzyme activity during re-energization and the other is a slower interaction which allows the physical dissociation of the inhibitor from the surface of the membrane into the soluble fraction. The amounts of inhibitor present on particles in our various protocols will be measured using our newly developed rat heart SMP ATPase titration procedure (1,2). The accuracy of this new procedure for the measurement of amounts of dog heart ATPase inhibitor on SMP has been verified by comparing it directly to an RIA developed especially for the measurement of the dog heart inhibitor (1). RIA procedures will be employed as well. The planned research will also address the question of the importance of ATPase inhibition in situ in mitigating tissue ATP depletion during myocardial ischemia. Our long term goals are to further characterize the interactions between the mitochondrial ATPase and its natural inhibitor and to quantitate further their pathophysiological significance in ischemic cardiac muscle.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
2R01HL030926-04
Application #
3341936
Study Section
Physical Biochemistry Study Section (PB)
Project Start
1984-09-01
Project End
1990-08-31
Budget Start
1987-09-01
Budget End
1988-08-31
Support Year
4
Fiscal Year
1987
Total Cost
Indirect Cost
Name
University of Cincinnati
Department
Type
Schools of Medicine
DUNS #
City
Cincinnati
State
OH
Country
United States
Zip Code
45221
Rouslin, W; Broge, C W (1996) Isoform-independent heart rate-related variation in cardiac myofibrillar Ca(2+)-activated Mg(2+)-ATPase activity. Am J Physiol 270:C1271-6
Rouslin, W; Broge, C W (1996) Novel difference in IF1 reactivity to Zn2+ in rabbit versus rat cardiomyocytes, mitochondria, and submitochondrial particles. Biochem Biophys Res Commun 227:8-14
Rouslin, W; Broge, C W (1996) IF1 function in situ in uncoupler-challenged ischemic rabbit, rat, and pigeon hearts. J Biol Chem 271:23638-41
Rouslin, W; Frank, G D; Broge, C W (1995) Content and binding characteristics of the mitochondrial ATPase inhibitor, IF1, in the tissues of several slow and fast heart-rate homeothermic species and in two poikilotherms. J Bioenerg Biomembr 27:117-25
Rouslin, W; Broge, C W; Guerrieri, F et al. (1995) ATPase activity, IF1 content, and proton conductivity of ESMP from control and ischemic slow and fast heart-rate hearts. J Bioenerg Biomembr 27:459-66
Rouslin, W; Broge, C W (1994) Analysis of factors affecting functional assays for estimating IF1, the mitochondrial ATPase inhibitor. Anal Biochem 222:68-75
Rouslin, W; Broge, C W (1993) Mechanisms of ATP conservation during ischemia in slow and fast heart rate hearts. Am J Physiol 264:C209-16
Rouslin, W; Broge, C W (1993) Factors affecting the species-homologous and species-heterologous binding of mitochondrial ATPase inhibitor, IF1, to the mitochondrial ATPase of slow and fast heart-rate hearts. Arch Biochem Biophys 303:443-50
Rouslin, W; Broge, C W; Chernyak, B V (1993) Effects of Zn2+ on the activity and binding of the mitochondrial ATPase inhibitor protein, IF1. J Bioenerg Biomembr 25:297-306
Rouslin, W; Broge, C W; Chernyak, B V (1992) Zn2+ allows differentiation between two kinds of IF1-ATPase interaction in intact mitochondria. Ann N Y Acad Sci 671:507-8

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