VMAX

Vmax is a term used to denote the maximum rate of a process in various scientific and engineering contexts. In biochemistry and enzymology, Vmax refers to the maximal rate of an enzymatic reaction when the substrate concentration is sufficiently high that all active sites are occupied. Under Michaelis-Menten kinetics, the reaction velocity V approaches Vmax as substrate concentration [S] becomes much greater than the Michaelis constant Km. The relationship is commonly written as V = (Vmax [S])/(Km + [S]). Vmax is determined by the total concentration of active enzyme and by the turnover number kcat, with Vmax = kcat [E]tot. Inhibitors can modulate Vmax: competitive inhibitors increase apparent Km without changing Vmax, while noncompetitive inhibitors decrease Vmax.

In pharmacology and pharmacokinetics, Vmax denotes the maximal rate of drug metabolism or elimination in a given system. When metabolic pathways become saturated, increases in drug concentration do not yield proportional increases in clearance, and the system can display zero-order kinetics with a nearly constant rate equal to Vmax.

In engineering and consumer products, Vmax is used to denote the top speed of a device or vehicle. The term appears in specifications for engines and in model names, such as high-performance motorcycles or other machinery where maximum velocity is a salient feature. Related concepts include Km, kcat, and the distinction between competitive and noncompetitive inhibition in enzyme kinetics.