A slow interconversion between active and inactive states of the (sodium + potassium ion)-dependent ATPase

Abstract

We have examined slow changes in the rate of ATP hydrolysis for purified dog kidney Na+ and K+ stimulated adenosine triphosphatase [(Na-K)ATPase] at various concentrations of free Mg2+, Mg-ATP, K+, and Na+. The effect of these ligands on the rate of ATP hydrolysis is explained by a rapid binding step determining the initial rate of turnover followed by a slow conformational change. Inactivation of enzyme stored in the presence of ethylenediaminetetraacetic acid occurs upon adding free Mg2+, Mg-ATP, and K+; reactivation may be achieved if the concentration of these ligands is reduced. Because of the slow conformational change, the affinities for ligands affecting inactivation are time dependent. A model is presented to explain the effects of free Mg2+ and Ma-ATP on (Na-K)ATPase activity.

A kinetic study of rat recombinant DNA polymerase β: detection of a slow (hysteretic) transition in polymerase activity and inhibition by butylphenyl-deoxyguanosine triphosphate

“…(Determination of initial velocity by assaying reactions at 1-min time points, before the slow transition in reaction velocity is detectable, yielded very similar values, attesting to the validity of the computer-derived parameters; Figure 2A.) The parameter [tau], which is the reciprocal of kob5, was also a hyperbolic function of dGTP concentration ( Figure 2B); similar data have been reported for the dog kidney Na+/K+-ATPase, another hysteretic enzyme (23). In contrast, steady-state velocity, vs5, showed a sigmoidal dependence on dGTP concentration ( Figure 3A).…”

Kinetic characterization of barley root plasma membrane‐bound Ca2+‐ and Mg2+‐dependent adenosine triphosphatase activities

“…From a general biological perspective, the barley root ATPase activities possess common characteristics with animal transport ATPase. The Ca^"*^ transport ATPase of sarcoplasmic reticulum (Neet andGreen 1977, DuPont 1977), Ca^"^-ATPase of human red blood cell membranes (Richards et al, 1978), and Na'', K+-ATPase (Cantley andJosephson 1976, Glynn andKarlish 1976) all possess kinetics indicating high and low affinity catalytic sites. Using methods essentially identical to those used in this study, Barron and Disalvo (1979) concluded that the Ca^"*"-and Mg^'^-dependent ATPase activities from bovine, aortic microsomes are ascribable to a single enzyme.…”

The Structure of Proteins Involved in Active Membrane Transport

“…Kinetic studies showing a negative cooperativity with respect to ATP suggest that both high and low affinity ATP sites exist (24,52), but whether these sites exist independently of one another or are intercon vertible is unknown. In contrast, in the absence of K +, the enzyme shows hyperbolic kinetics and only a high affinity site (141).…”