Figure 2.

Enzyme kinetics described by ATX and choline oxidase for the hydrolysis of their physiological substrates. A, the kinetics of ATX lysoPLD activity (20 nm) on LPC result in a double exponential-sigmoid choline secretion that can be measured by a coupled reaction with choline oxidase and HRP. This behavior is independent of the presence of delipidated BSA acting as an LPC vehicle. B, Michaelis–Menten kinetics derived from the linear part of lysoPLD activity measurements, as the ones shown in A. C, choline chloride oxidation by choline oxidase follows a single exponential kinetics. D, Michaelis–Menten kinetics for choline oxidase. In all cases, 1 unit/ml choline oxidase and 1 unit/ml HRP were used for the coupled assay. Data represent the averaged data of triplicate measurements. Error bars, S.E.