Purification of a plasma membrane-bound lipoxygenase from soybean cotyledons

In this work a plasma membrane-bound lipoxygenase (LOX) from soybean (Glycine max L. Merr.) cotyledons was purified to homogeneity by ion exchange and gel filtration chromatography. The enzyme has a molecular mass of ≈92 kDa and exhibits a maximal activity in the alkaline pH range (7.5–10). The activity, evaluated both as conjugated diene formation and oxygen consumption, is almost the same as linolenic or linoleic acid (Km=25 and 30 μM, respectively), and is inhibited by typical LOX inhibitors (nordihydroguaiaretic acid or propyl gallate). The reaction product is 13-hydroperoxy-octadecadienoic acid, when linoleic acid is used as a substrate. The biochemical and molecular characteristics of this enzyme are very similar to those of soluble LOX 1 from soybean cotyledons. Therefore, it is suggested that soluble enzymes may be transferred, by vesicles, to membranes where they may attack more easily polyunsaturated fatty acids, linked to phospholipids or liberated by membrane-bound phospholipases.