PARTICULATE AND SOLUBLE LIPOXYGENASE ISOENZYMES - COMPARISON OF MOLECULAR AND ENZYMATIC-PROPERTIES

Cucumber (Cucumis sativus L.) cotyledons, a plant model system for stu dying changes in metabolic compartmentation, contain at least six form s of lipoxygenase. The intracellular location and organellar topology of lipoxygenase forms in lipid bodies, microsomes, and cytosol were in vestigated. A protocol was worked out to solubilize and prepare lipid- body lipoxygenase in an enzymatically active form. The methodology req uired for the solubilization of the lipid-body form differed from the procedure applicable for solubilization of two lipoxygenase forms from the microsomal membranes. Three cytosolic lipoxygenases were purified and found to be distinguishable from each other in size and charge. F urther characterization and differentiation of all cellular lipoxygena se isoforms was achieved by comparison of the enzymatic properties. Ma rked differences in pH optima of the particle-bound lipoxygenases were found: optimal pH of 8.5 for lipid-body lipoxygenase and pH 5.5 for t he microsomal lipoxygenases. In addition, analysis of the products for med showed that the catalytic properties of lipid-body lipoxygenase an d microsomal lipoxygenase are clearly distinguishable from each other and from the soluble forms.