Sterol synthesis, bacteria

Biotin is a growth factor for many bacteria, protozoa, plants, and probably all higher animals. In the absence of biotin, oxalacetate decarboxylation, oxalosuccinate carboxylation, a-ketoglutarate decarboxylation, malate decarboxylation, acetoacetate synthesis, citrulline synthesis, and purine and pyrimidine syntheses, are greatly depressed or absent in cells (Mil, Tl). All of these reactions require either the removal or fixation of carbon dioxide. Together with coenzyme A, biotin participates in carboxylations such as those in fatty acid and sterol syntheses. Active C02 is thought to be a carbonic acid derivative of biotin involved in these carboxylations (L10, W10). Biotin has also been involved in... 

GC data should be evaluated carefully. The main sterols of interest are cholesterol and lathosterol, the latter being a late-stage intermediate in cholesterol synthesis. Coprostanol is formed by the action of colonic bacteria on cholesterol and may vary considerably between mice. Peaks for coprostanol and other minor animal-derived sterols appear very close to, and may overlap with, that of cholesterol. Lathosterol is usually resolved between the cholesterol and the first phytosterol peak. Neutral sterol excretion should be reported as the sum of cholesterol, its precursors, and its derivatives. Evaluation excluding precursors is also appropriate. 

Sterols comprise a very important class of compounds in plant and animal systems. Bacteria and other organisms utilize cholesterol or related sterols in the synthesis and maintenance of their cell walls. True sterols are present in cyanobacteria to only a very small degree they are largely replaced with a steroid-like class of triterpenoid known as the hopanoids. The carbon frameworks of sterols and bacterial hopanoids are synthesized in essentially the same manner as other terpenes, however, the cyclization reactions to yield their polycyclic skeletons are unique. A variety of sterols and hopanoids are found in cyanobacteria and they are believed to have important cellular functions in cell wall structure and function. " As discussed in Section 2.06.5, many of the hopanoids also possess a polyalcohol chain derived from a sugar. ... 

Bacteria, synthesis, 65 Bacteriohopane skeleton formation, pentacyclic C35, See Pentacyclic C35 bacteriohopane skeleton formation Bees, sterol metabolism, 131,132/133 Beetles, sterol metabolism, 133-134... 

Bacterial isoprenoid synthesis - the Rohmer pathway Current biosynthetic evidence indicates that the steps from IPP to isoprenoids in Eubacteria are the same as those in eukaryotes [62-69] (see [70-73] for literature). Especially the incorporation of C-labeled precursors into prokaryotic hopanoids, sterol surrogates in bacterial membranes (see [73] and literature cited therein), or into ubiquinone-8 [70] has revealed that the classic pathway of IPP formation starting from acetyl-CoA via acetoacetyl-CoA, HMG-CoA, MVA, MVA-P, and MVA-PP does not exist in a great variety of bacteria, including E. coli Zymomonas mobilis, Methylobacterium organophilum, Rhodopseudomonas palustris, R. acidophila, Acetobacter aceti ssp. xylinum, but also in the thylakoids of the cyanobacterium Synechocystis sp. [74]. 

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