Presqualene metabolism in two species of Lagenidium

The fate of precursors of the isoprenoid pathway was studied in the sterol auxotroph Lagenidium giganteum and in the positive control organism Lagenidium callinectes. Acetate derived from glucose and mevalonic acid was converted to sterols and fatty acids in L. callinectes. Lagenidium giganteum converted mevalonic acid to sterols and fatty acids, but glucose-derived acetate was not utilized for sterol synthesis. The results showed that the defect in the isoprenoid pathway of L. giganteum occurs at the level of the beta-hydroxy-beta-methylglutarylcoenzyme A reductase-synthase complex. Various aspects of this defect are discussed relative to metabolism of the organism.