ATPHydrolyseRate

ATPHydrolyseRate refers to the rate at which adenosine triphosphate (ATP) is hydrolyzed to adenosine diphosphate (ADP) and inorganic phosphate (Pi) by enzymes such as ATPases or by other enzymes that carry out ATP-dependent reactions. It is a fundamental parameter in biochemistry and cell biology, reflecting the catalytic activity of proteins that drive energy transduction and mechanical work.

Under defined conditions, the rate is described by the initial velocity V0 and, for Michaelis–Menten kinetics, by V0 = (Vmax [ATP])/(Km + [ATP]). Vmax represents the maximal rate at saturating ATP, and kcat (Vmax divided by the enzyme concentration) is the turnover number, typically expressed in s^-1. Rates are commonly reported as μmol of Pi released per minute per milligram of protein (μmol Pi min^-1 mg^-1) or as kcat values.

Several factors influence ATP hydrolysis rate, including the presence of Mg2+ as a cofactor, pH, temperature, ionic strength, substrate concentration, and regulatory subunits or interacting proteins. In motor proteins or ATP synthase, mechanical load or conformational state can markedly affect observed rates. In vivo, rates are modulated by cellular localization, substrate channeling, and allosteric regulation.

Measurement methods include colorimetric or luminescent assays for inorganic phosphate release (e.g., malachite green), radiolabeled ATP assays, and ATPase-specific luminescence assays such as those based on ATP depletion or ADP detection. These measurements yield kinetic parameters that aid in comparing enzymes and assessing inhibitors or activators.

Examples of ATPases with well-characterized hydrolysis rates include Na+/K+-ATPase, actomyosin ATPase, and the F1-ATPase component of ATP synthase, which utilize hydrolysis or turnover of ATP to perform work.