| Abstract: | Alkaline phosphatase (EC 3.1.3.1) activity in bovine aortic endothelial cells in culture was stimulated in a synergistic manner by 10(-6) M retinol and by 10(-7) M dexamethasone. An early exposure to retinol was required for maximum stimulation and could be reproduced by the addition, during growth, of 2 micrograms/ml compactin. The induced enzyme activity in cell lysates prepared from cells treated with retinol and dexamethasone had a Vmax that was 50-fold that of the controls. The stimulatory effect of retinol could be partially reversed by the addition of sonic dispersions made from cholesterol and phosphatidylcholine. The incorporation of [14C]acetate into saponifiable and non-saponifiable cellular lipids was inhibited by 10(-6) M retinol but the activities of 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) and 3-hydroxy-3-methylglutaryl coenzyme A synthase (EC 4.1.3.5) remained unaffected. The results suggest that retinol might inhibit lipid biosynthesis through an alternate mechanism. |
