The biosynthesis of sterols in higher plants

Abstract

1. [2-(14)C]Mevalonate was incorporated into squalene and the major phytosterols of pea and maize leaves; it was also incorporated into compounds belonging to the 4,4-dimethyl and 4alpha-methyl steroid groups and which may be possible phytosterol intermediates. 2. l-[Me-(14)C]Methionine was incorporated into the major sterols and also into the 4,4-dimethyl and 4alpha-methyl steroid groups. No radioactivity was detected in squalene. 3. Under anaerobic conditions incorporation of [2-(14)C]-mevalonate into the non-saponifiable lipid of pea leaves was drastically decreased but radioactive squalene was accumulated. 4. Cycloartenol, 24-methylenecycloartanol, 24-methylenelophenol, 24-ethylidenelophenol, fucosterol, beta-sitosterol, stigmasterol and campesterol have been identified by gas-liquid chromatography in pea leaves. 5. The significance of these results in connexion with phytosterol biosynthesis and the introduction of the alkyl group at C-24 into phytosterols is discussed.

Terpene Biosynthesis in Cell-free Extracts and Excised Shoots from Wedgwood Iris

“…The 4,4-dimethylsterols are common products of MVA-2-VC incorporation in plants and are thought to be intermediates of phytosterol biosynthesis (11). Perhaps the 6-hr incubation time of the present study was not sufficient for accumulation of radioactive phytosterols which are farther along the biosynthetic pathway than 4,4-dimethylsterols in which radioactivity was detected.…”

“…The lack of net evolution of "CO2 from MVA-2-"C by excised iris shoots is to be expected, since only radioactive 4,4-dimethylsterols were detected. Decarboxylation of triterpene intermediates of phytosterol biosynthesis occurs subsequent to the formation of the 4, 4-dimethylsterols (11). Since labeled terpene alcohols did not accumulate when excised shoots were fed MVA-2-"C, evolution of"CO20 from prenoic acids (9, 21) would not be expected.…”

Studies in Phytosterol Biosynthesis: Observations on the Biosynthesis of Fucosterol in the Marine Brown Alga Fucus spiralis

“…These labelled compounds were then used to obtain the data described below. A portion of the squalene (66,070 dis./min of 3H, 9,266 dis./min of 1%) was added to 10 mg of carrier squalene and purified by the thiourea clathrate [12]. The squalene obtained had a 3H/14C ratio of 7.17, corrected 3H/14C = 5.8116.…”

“…The ,! ?-carotene (which included small amounts of a-carotene) was dissolved in 0.5 ml of toluene and decolourised [12] prior to addition of the scintillator solution and radioassay ; 1,307dis.lminof 3H; 231dis./minof14C,3H/14C = 5.66; corrected 3H/14C = 6.1218. This ratio is in agreement with that previously reported for ,!…”

“…MVA, mevalonic acid; Tlc, thin ayer chromatography. liminary reports [7,8]. Evidence for the occurrence in Fucus spiralis of cycloartenol (11), the postulated phytosterol precursor 11,9,101, is also present,ed.…”