An Evolved Aminoacyl-tRNA Synthetase with Atypical Polysubstrate Specificity,

Abstract

In the presence of natural (liver mitochondria and microsomes) and artificial (liposomes from saturated phosphatidyl cholines) membranes, the rate of oxidation of an emulgated polyunsaturated fatty acid by reticulocyte lipoxygenase sharply increases and correlates with the amount of polyunsaturated fatty acid incorporated into the membrane. Hydrolysis of egg lecithine polyunsaturated acyls by phospholipase A2 drastically increases the rate of their enzymatic oxidation. It was shown that 15-hydroperoxyarachidonate is incorporated into lecithine liposomes at a much slower rate that the non-oxidized arachidonic acid. Solubilization of membranes with a detergent leads to the disappearance of the activating effect. Addition of saturated lecithine liposomes results in quenching of protein fluorescence of reticulocyte lipoxygenase, thus suggesting conformational changes in the enzyme structure upon its interaction with the membrane. The experimental results suggest that free polyunsaturated membraneous fatty acids are physiological substrates for animal lipoxygenases. One possible reason for the elevated rate of the lipoxygenase reaction in membranes is the alteration of enzyme conformation upon its interaction with the membrane matrix.