Salicylhydroxamic acid inhibits Δ6 desaturation in the microalga Porphyridium cruentum

Treatment of the microalga Porphyridium cruentum with salicylhydroxamic acid (SHAM) inhibited growth and affected fatty acid composition. At a relatively low concentration (40 mu M?) SHAM predominantly inhibits Delta 6 desaturation. The effect of the inhibitor was most intense in phosphatidylcholine (PC) and phosphatidylothanolamine, in which the proportions of the downstream products of the Delta 6 desaturase were reduced, whereas that of the substrate, 18:2 increased. As a result of the availability of 18:3, 18:3 omega 3, which under normal conditions is not observed, appeared predominantly in chloroplastic lipids. Pulse labeling with linoleic acid has shown that SHAM? inhibits Delta 6 desaturation almost immediately, suggesting an apparent inhibition of the activity of the desaturase, rather than its synthesis or that of its cofactors. Furthermore, the addition of gamma-linolenic acid to SHAM-inhibited cultures relieved the inhibition. Following exposure to the inhibitor, 18:3 omega 3 appeared first in chloroplastic glycolipids and only later in PC, indicating that the former are the substrates for the first dedicated step of the proposed omega 3 pathway in this alga. (C) 1999 Elsevier Science B.V. All rights reserved.