Akademik

Rate of movement; specifically, distance traveled or quantity converted per unit time in a given direction. Cf.:speed. [L. velocitas, fr. velox (veloc-), quick, swift]

- initial v. the rate of a reaction, e.g., an enzyme-catalyzed reaction, at the early stages of the reaction such that the product(s) concentrations have not risen to a level to significantly affect the observable rate; typically, initial velocities are observed when less than 10% of the reaction's approach toward equilibrium has occurred. SYN: initial rate.

- maximum v. (V_max) 1. the maximum rate of an enzyme-catalyzed reaction that can be achieved by progressively increasing the substrate concentration at a given enzyme concentration; in cases of substrate inhibition, V_max is an extrapolated value in the absence of such inhibition; Cf.:Michaelis-Menten equation. 2. the maximum initial rate of shortening of a myocardial fiber that can be obtained under zero load; used to evaluate the contractility of the fiber.

- nerve conduction v. the rate of impulse conduction in a peripheral nerve or its various component fibers, generally expressed in meters per second.

- PSA v. a measure of the rapidity of change in a person's PSA level.

- sedimentation v. the rate of movement of a substance, typically a macromolecule, in centrifugation; these centrifugation studies provide data on the structure of the macromolecule.

- steady-state v. the v. of an enzyme-catalyzed reaction in which, over the time course of the study, the concentration of any enzyme species is constant ( i.e., for an enzyme-substrate binary complex, ES, d[ES]/dt ≈ 0; for this to hold true, the total enzyme concentration must be much less than the initial substrate concentration. SYN: steady-state rate.