Soybean Lipoxygenase

The reliability of the assay of lipoxygenase has been improved by minimising sources of error, such as the adherence of the enzyme to the glass of the containing vessel. The electrophoretic method of preparing crystalline lipoxygenase has been improved, and a new chromatographic purification has been developed. The shape of the pH‐activity profile of the enzyme has been shown to depend critically upon the amount of organic solvent present in the solution, as well as upon its ionic strength. These effects are discussed, and an attempt has been made to fit theoretical curves to the pH‐profiles in solutions containing no organic solvents. The dissociation constants for the ionisable groups on the enzyme extracted from these data are pKa= 6.5‐6.8 and pKb= 9.0‐9.1, in 0.2 M Tris. Micelle formation has little effect on the Km of the enzyme. However, substrate concentration vs. activity curves show perturbations at the critical miselle concentration in certain instances, and a possible relationship between the critical micelle concentration and a substrate concentration derived by extrapolation of the activity curves is presented.