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Kinetic modalities of ATP synthesis. Regulation by the mitochondrial respiratory chain.

1986; Elsevier BV; Volume: 261; Issue: 30 Linguagem: Inglês

10.1016/s0021-9258(18)66976-5

1083-351X

Akemi Matsuno‐Yagi, Youssef Hatefi,

ATP Synthase and ATPases Research

Two interconvertible kinetic modes are described for ATP synthesis by bovine heart submitochondrial particles.One mode is characterized by low apparent K , values for ADP (6-10 p ~) and Pi (50.25 mM), and a limited capacity for ATP synthesis (apparent Vmax -500 nmol ATP*min"*mg of protein").ATP synthesis occurs predominantly in this mode when the coupled activity of the respiratory chain relative to the number of functional ATP synthase complexes is low.The second kinetic mode is characterized by high apparent K,,, values for ADP (50-100 p ~) and Pi (-2.0 mM) and a high capacity for ATP synthesis (VmaX > 1800 nmol ATP*min"*mg of protein").This mode of ATP synthesis predominates when the available free energy relative to the number of functional ATP synthase units is high.These results suggest that energy pressure in mitochondria might regulate ATP synthesis such that at low levels of energy the ATP synthase operates economically (low substrate K , values, low turnover capacity for ATP synthesis), while at high levels of energy these kinetic constraints are relaxed (high substrate K,,, values, high turnover capacity for ATP synthesis).The implications of these findings are discussed in relation to (a) the cooperative-type kinetics of ATP synthesis and hydrolysis, (b) the differential effects of a number of Fo-F1 inhibitors on the rates of ATP synthesis and hydrolysis, and (c) the controversy as to whether protonic energy in mitochondria is localized or delocalized.Mitochondrial F1-ATPase is composed of five unlike subunits with the stoichiometric ratio of a3P3y6c (1)(2)(3).Each molecule of the enzyme is considered to have three functional catalytic sites on the / 3 (or the a@) subunits (1-3).The kinetics of ATP hydrolysis by isolated and membrane-bound Fl-ATPase have suggested site-site cooperativity (4-8).Results have indicated negative cooperativity with respect to [MgATP] and positive cooperativity in the sense that substrate binding to the second and third sites greatly enhances turnover at the first site by accelerating the rate of product release (7).Analysis of the kinetics of ATP hydrolysis by isolated F1-ATPase over a wide range of substrate concentration (1-5000 HM MgATP) indicated three apparent KkTp values in the