stigmasterol and 24-methylenecholesterol

We have identified the function of the Arabidopsis DIMINUTO/DWARF1 (DIM/DWF1) gene by analyzing the dim mutant, a severe dwarf with greatly reduced fertility. Both the mutant phenotype and gene expression could be rescued by the addition of exogenous brassinolide. Analysis of endogenous sterols demonstrated that dim accumulates 24-methylenecholesterol but is deficient in campesterol, an early precursor of brassinolide. In addition, we show that dim is deficient in brassinosteroids as well. Feeding experiments using deuterium-labeled 24-methylenecholesterol and 24-methyldesmosterol confirmed that DIM/DWF1 is involved in both the isomerization and reduction of the Delta24(28) bond. This conversion is not required in cholesterol biosynthesis in animals but is a key step in the biosynthesis of plant sterols. Transient expression of a green fluorescent protein-DIM/DWF1 fusion protein and biochemical experiments showed that DIM/DWF1 is an integral membrane protein that most probably is associated with the endoplasmic reticulum.

Topics: Amino Acid Sequence; Arabidopsis; Arabidopsis Proteins; Base Sequence; Brassinosteroids; Cholestanols; Cholesterol; DNA, Plant; Gene Expression Regulation, Plant; Genes, Plant; Membrane Proteins; Molecular Sequence Data; Mutation; Phenotype; Phytosterols; Plant Growth Regulators; Plant Proteins; RNA, Messenger; RNA, Plant; Sequence Homology, Amino Acid; Steroids; Steroids, Heterocyclic; Stigmasterol

To investigate the metabolism and possible deleterious effects of 4-methyl and 4,4-dimethyl steroids in Manduca sexta, the 4,4-dimethyl sterols lanosterol and cycloartenol, the 4-methyl sterol obtusifoliol and the 4,4-dimethyl pentacyclic triterpenoid alpha-amyrin were fed in an artificial agar-based diet at various concentrations. Utilization and metabolism of these four compounds were compared with sitosterol, stigmasterol, brassicasterol, ergosterol and 24-methylenecholesterol, 24-alkyl sterols that are readily dealkylated and converted to cholesterol in Manduca and in most phytophagous insects. None of the 4-methylated compounds significantly inhibited development except at very high dietary concentrations. The delta 24-bonds of lanosterol and cycloartenol were effectively reduced by the Manduca delta 24-sterol reductase enzyme, as is the delta 24-bond of desmosterol which, in most phytophagous insects, is an intermediate in the conversion of sitosterol, stigmasterol and other C28 and C29 phytosterols to cholesterol. On the other hand, the 24-methylene substituent of obtusifoliol was not dealkylated. Each of the 4-desmethyl C28 and C29 sterols was readily converted to cholesterol, and a significant amount of 7-dehydrocholesterol was derived from ergosterol metabolism. The reason for the differences in substrate specificity of these sterols is not clear, but the information may be useful in the development of new, specific, mechanism-based inhibitors of sterol metabolism.

Topics: Animals; Cholestadienols; Cholesterol; Ergosterol; Manduca; Phytosterols; Sitosterols; Sterols; Stigmasterol

Quantitative analysis of the local distribution of four noncholesterol sterols, 24-methylene cholesterol, campesterol, stigmasterol, and beta-sitosterol, and of the local distribution of cholesterol in gallstones was performed by mass spectrometry, with D6-cholesterol as an internal standard. The role played by trace amounts of these four noncholesterol sterols in the formation of gallstones was investigated by comparing the amounts of these sterols in different parts of gallstones. It was found that the amounts of the noncholesterol sterols in the inside part were significant greater than the amounts in the outside part of various structural types of gallstones. However, the distribution of the cholesterol did not show such variation. The amounts of noncholesterol sterols distributed locally suggested that these sterols play a role in the formation of gallstones.

Topics: Cholelithiasis; Cholesterol; Female; Gas Chromatography-Mass Spectrometry; Humans; Male; Middle Aged; Phytosterols; Sitosterols; Sterols; Stigmasterol

Anaerobically grown Saccharomyces cerevisiae retained the ability to transfer a C1-group to the C-24 position of a delta 24(25)-sterol and to reduce the delta 25(28)-bond of a 24-methylenesterol. Both desmosterol and 24-methylenecholesterol yielded 24 beta-methylcholesterol. However, when the substituent at C-24 was enlarged to a 24-ethylidene group (fucosterol), reduction of the delta 24(28)-bond did not occur. In no cases was a delta 7- or a delta 22-bond introduced. Because the delta 24(28)-bond was reduced in the absence of the delta 22-bond, the delta 22-bond is not an obligatory requirement for reduction.

Topics: Anaerobiosis; Cholesterol; Desmosterol; Models, Biological; Oxidation-Reduction; Saccharomyces cerevisiae; Stigmasterol