STUDIES ON A LIPOXIDASE SYSTEM FROM SUNFLOWER SEEDS AND SEEDLINGS

Abstract

Lipoxidase activity was obtained in enzyme preparations from sunflower seeds and seedlings. A partly purified preparation from seedlings was used for enzyme kinetic studies. The pH optimum was 6.8 and 100% oxygen was required for maximum activity. The Michaelis constant, with potassium linoleate as substrate, was 1.64 × 10−3 M. The reaction products were conjugated dienes. Enzyme activity was not affected by various metal and sulphydryl inhibitors nor by α-tocopherol, but catechol, α-naphthol, ethanol, and potassium oleate were inhibitory. Oil from flax, rape, and sunflower seeds reduced total oxidation of linoleate by the enzyme. Copper sulphate increased the rate and total oxidation of the linoleate–lipoxidase system, but iron, manganese, magnesium, and calcium were without effect. Lipoxidase activity was associated with mitochondrial (15,000 × g), intermediate (25,000 × g), and microsomal (100,000 × g) fractions, as well as with the soluble cytoplasmic proteins. Lipoxidase activity in seedlings increased during initial stages of germination, then decreased. The most rapid depletion of total fat in the seedlings coincided with maximum lipoxidase activity.