Adenosine triphosphatase hydrolysis

Stein, L.A., Schwarz, R., Chock, P.B., Eisenberg, E. (1979). Mechanism of actomyosin adenosine triphosphatase. Evidence that adenosine 5 -triphosphate hydrolysis can occur without dissociation of the actomyosin complex. Biochemistry 18, 3895-3909. 

Similarly, specific catalysts called enzymes are important factors in determining what reactions occur at an appreciable rate in biological systems. For example, adenosine triphosphate is thermodynamically unstable in aqueous solution with respect to hydrolysis to adenosine diphosphate and inorganic phosphate. Yet this reaction proceeds very slowly in the absence of the specific enzyme adenosine triphosphatase. This combination of thermodynamic control of direction and enzyme control of rate makes possible the finely balanced system that is a hving cell. 

Mitchell, P., and J. Moyle, Stoichiometry of proton translocation through the respiratory chain and adenosine triphosphatase systems of rat liver mitochondria. Nature 208 147, 1965. The initial observations that electron transport moves protons outward across the mitochondrial inner membrane and that ATP hydrolysis does the same. 

This is the so-called sodium-potassium pump, catalyzed by adenosine triphosphatase ATP-ase ATP hydrolysis supplies the energy. 

On hydrolysis, particularly under the action of the enzyme adenosine triphosphatase (ATPase), ATP is converted into adenosine diphosphate (ADP) and phosphate. This process is of great importance in metabolism (see p, 246). Under ordinary physiological conditions ATP bears four negative charges, as shown above. 

The magnitudes of entropies of activation have provided valuable information regarding the details of the interactions between enzymes and substrates. The process of muscular contraction involves an interaction between the muscle enzyme myosin and adenosine triphosphate (ATP). Myosin is an enzyme which catalyzes the hydrolysis of ATP, a process which we have seen (p. 246) to be more exergonic than is the case for many other phosphates, and this hydrolysis contributes energy for contraction. Because of its catalytic action, myosin is also referred to as adenosine triphosphatase (ATP-ase). When the activated complex is formed from ATP ase and its substrate ATP, the entropy of activation is about 41 cal K" mol under approximately normal physiological conditions. We saw on p. 400, on the basis of a very simple electrostatic theory of AS values for ionic reactions in aqueous solution, that there will be a positive contribution of about 10 cal mol for each unit of the product [ [ % ( The long myosin molecules bear a series of positive... 

Petrack B, CrastonA, Sheppy F and Farron F (1965) Studies on the hydrolysis of adenosine triphosphatase by spinach chloroplasts, J.Biol.Chem. 240, 906-914. 

---