Lipoxygenase-mediated cleavage of fatty acids in plant mitochondria [Brassica oleracea, calcium, phosphatidic acid, phospholipase D, unsaturated fatty acids, lipoxygenase, malondialdehyde, cauliflowers]
1981
Dupont, J. (Paris-6 Univ. (France). Lab. de Biologie Vegetale 4)
Incubation of cauliflower bud mitochondria in the presence of 5mM CaCl(,2) results in a rapid hydrolysis of the main membrane phospholipids. Under the action of phospholipase D, phosphatidic acid is produced and forms, within the membranes, a very labile complex with Ca('2+) and HPO('2-)(,4) ions present in the incubation medium. With time, one observes a first step characterized by the formation of phosphatidic acid, followed by a second step linked to the breakdown of this phospholipid. The enzyme responsible for the disappearance of phosphatidic acid has been identified as lipoxygenase. In the presence of molecular oxygen, this enzyme acts on the polyunsaturated fatty acids of phosphatidic acid (mainly C(,18:2) and C(,18:3)) yielding small water-soluble molecules, one of them being identified as malondialdehyde (1,3-propanedial). Experiments involving inhibitory conditions of the breakdown of phosphatidic acid indicate that lipoxygenase acts directly on membrane-bound phosphatidic acid without previous involvement of a lipolytic acyl hydrolase activity. In addition, the lipoxygenase activity is fully sensitive to hydroxamate derivatives. It is proposed that the lipoxygenase activity may account for a part of the mitochondrial alternative electron pathway that is insentive to cyanide.
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