Cholesterol synthesis in rat brain: differential incorporation of mevalonolactone-2-C14 and potassium mevalonate-2-C14

METABOLISM OF MEVALONIC ACID BY LACTOBACILLUS PLANTARUM

Durr, I. F. (American University of Beirut, Beirut, Lebanon), and A. N. Shwayri. Metabolism of mevalonic acid by Lactobacillus plantarum. J. Bacteriol. 88:361-366. 1964.-Lactobacillus plantarum strain 8014-H(2), unlike other lactobacilli studied, does not require mevalonic acid for growth, but growing and resting cells utilize it only for the synthesis of nonsaponifiable lipids. Upon the incubation of washed cells with mevalolactone-2-C(14), the label appeared in the lipids but not in CO(2). On the other hand, when mevalolactone-1-C(14) was used, the label appeared in CO(2) but not in lipids. For every mole of CO(2) liberated, 1 mole of radioactive carbon was introduced in the lipids, suggesting that terpenic polymers were synthesized. Amino acids did not stimulate the utilization of mevalonic acid. Starved cells could not synthesize nonsaponifiable lipids from mevalonic acid unless glucose was supplied. Sodium fluoride (0.14 m), 2,4-dinitrophenol (0.003 m), p-hydroxymercuribenzoate (0.0013 m), potassium phosphate (0.1 m), and ammonium formate (0.04 m) were potent inhibitors. Cells metabolized only one isomer of dl-mevalonic, and utilized the salt form at least twice as efficiently as the lactone. Optimal synthesis of lipids from mevalonic acid occurred aerobically, at pH 5 and 30 C.

Biosynthesis of thiamine. Incorporation experiments with 14C-labelled substrates and with (15N)glycine in Saccharomyces cerevisiae

1. Yeast was grown in a minimal synthetic medium together with a range of (14)C-labelled substrates under standardized conditions. After isolation, the purified thiamine was cleaved by sulphite and the pyrimidine and thiazole moieties were purified and assayed for radioactivity. 2. In order of decreasing incorporation, [(14)C]formate, [3-(14)C]serine, [2-(14)C]glycine and [2-(14)C]acetate supplied label for the pyrimidine, and [2-(14)C]glycine, [3-(14)C]serine, [1-(14)C]glycine, [(14)C]formate and [2-(14)C]acetate for the thiazole. Incorporation of label into the fragments from several other (14)C-labelled substrates, including [Me-(14)C]- and [3,4-(14)C(2)]-methionine, was insignificant. 3. [3-(14)C]Serine was shown not to contribute label to C-2 of the thiazole ring. 4. Significant incorporation of nitrogen from [(15)N]glycine into the thiazole moiety, but not into the pyrimidine moiety, was established. 5. It appears that C-2 and N-3 of the thiazole ring are formed from C-2 and the nitrogen atom of glycine, but the entire methionine molecule does not appear to be implicated.