title: On the role of actomyosin ATPases in regulation of ATP turnover rates during intense exercise.
abstract: Actomyosin ATPase is the dominant ATP sink during muscle work. Its catalytic capacities in fast-twitch oxidative glycolytic fibers have long been known to exceed by about 3-fold those of slow-twitch oxidative fibers, but the relative contributions to control of metabolic rates during exercise have never been closely examined. We compared fast-twitch oxidative glycolytic and slow-twitch oxidative fibers that displayed similar mitochondrial abundance (similar activities of mitochondrial marker enzymes). During short-term, but near maximum, aerobic exercise, fast-twitch oxidative glycolytic fibers displayed ATP turnover rates that were 2-4 times higher than for slow-twitch oxidative fibers (despite similar mitochondrial metabolic capacities), implying a large ATPase contribution to control of maximum metabolic rate. Fluxes through the ATP in equilibrium ADP + Pi cycle were extremely well regulated; at the lower limit, the forward flux exceeded the backward flux by only 0.06%, whereas at the upper limit, ATPase rates exceeded ATP synthesis rates by 0.12%. This very high precision of energy coupling could not be easily explained by standard metabolic regulation models.
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, Canada.
authors.forename: P W
authors.initials: PW
authors.lastname: Hochachka
authors.forename: M S
authors.initials: MS
authors.lastname: Bianconcini
authors.forename: W S
authors.initials: WS
authors.lastname: Parkhouse
authors.forename: G P
authors.initials: GP
authors.lastname: Dobson
mesh_terms: D015094:3-Hydroxyacyl CoA Dehydrogenases / Q000378:metabolism; D000205:Actomyosin / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002334:Carnitine O-Palmitoyltransferase / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000378:metabolism; D004734:Energy Metabolism; D005969:Glutamate Dehydrogenase / Q000378:metabolism; D006019:Glycolysis; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000378:metabolism; D008297:Male; D008931:Mitochondria, Muscle / Q000378:metabolism; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D009218:Myosins / Q000378:metabolism*; D009711:Nucleotides / Q000378:metabolism; D010085:Oxidative Phosphorylation; D005082:Physical Exertion; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D007773:Lactates; D009711:Nucleotides; D000255:Adenosine Triphosphate; D000205:Actomyosin; D015094:3-Hydroxyacyl CoA Dehydrogenases; D005969:Glutamate Dehydrogenase; D002334:Carnitine O-Palmitoyltransferase; D002950:Citrate (si)-Synthase; D009218:Myosins