Higher Plant Steroids

The following fungal and higher plant steroids have now also been isolated from lichen species ergosterol-5,8-peroxide (525), cholestan-3P-ol, 24-methylcholestan-3 P-ol, 24-ethylcholestan-3 P-ol, 24-methylcholest-7-en-3P-ol, 24-ethylcholest-7-en-3P-ol, cholest-5-en-3P-ol, 24-methylcholest-5-... 

Donath J, Boland W (1994) Biosynthesis of acyclic homoterpenes in higher plants parallels steroid hormone metabolism. J Plant Physiol 143 473 78... 

There are several natural non-combustion sources of PAHs. A study in 1980 by Wakeham [43] concluded that phenanthrene could be created by the dehydrogenation of steroids, retene could be produced by the diagenesis of abietic acid, and alkyl chrysenes could form from the degradation of the pentacyclic triterpenes alpha- and beta-amyrin, which are components of higher plant waxes. In this section we will look at the natural non-combustion sources of retene and perylene and how these sources might impact the Great Lakes. 

The earliest steps (MVA to GGPP) for polyisoprenoid biosynthesis are identical for all plants and animals (12,13). They involve the well-known diterpene pathway, MVA — MVAP — MVAPP — IPP + DMAPP — GPP — FPP — GGPP. The enzymes catalyzing these steps have been studied extensively, especially from animals (liver) and yeast, and to a more limited extent from higher plants. In some cases the enzymes have been purified to homogeneity most have been only partially purified. In both plants and animals a major branch at FPP leads to the production of squalene and the steroids. In plants, three major branches occur at GGPP, of which one leads to the carotenoids via phyto-ene, a second to the phytyl group of chlorophyll, and a third to the GAs. 

The structurally related antibiotics kirromycin and pulvomycin both act upon EF-Tu of most bacteria (and chloroplasts) although not upon its eucaryal (EF-la) counterpart [158,159]. The steroid antibiotic fusidic acid interacts systematically with both the eucaryal (EF-2) and the bacterial (EF-G) translocating factors, including chloroplasts of higher plants. Diphtheria toxin (fragment A) discriminates between bacterial-mitochondrial and eucaryal translocating factors by selectively and irreversibly impairing the eucaryal EF-2 factors [160,161]. 

Summary of Biomarker Analyses. The combination of phospholipid fatty acids, steroids, and lignin phenols indicates that the chemical makeup of raw foam includes input from bacterial, algal, diatoms, fungal, and higher plant sources. The total of these compounds account for less than 5% of the organic carbon present in raw foam, and it is not possible, therefore, to assess which is the largest source. These compounds however, do reveal interesting compositional trends between the raw foam and the stream and foam humic substances. The compositional complexity of humic substances increases from stream, to foam, to foam extract and from fulvic acids to humic acids. 

The method of identifying particular carbon atoms in these polycyclic compounds is by a systematic numbering sequence. Individual rings are also denoted alphabetically. The conventions for steroids and hopanoids are shown in Fig. 2.20a. Numbering for higher plant triterpenoids follows a similar sequence to that of hopanoids, with C-22 being incorporated in the six-membered E ring, and C-29 and C-30... 

All of the above results refer to rat liver systems. Presumably, the same result also applies to lanosterol (73) preparedby feeding yeast with [2- C,2R- H,3R]mevalonic acid or its (2S)-isomer. However, although steroids are widely distributed in nature (see also Section 13), the first formed triterpenoid in higher plants (with the exception of certain Euphorbia sp. ) is cycloartanol (75). As expected, 2,3-oxidosqualene (71) is incoi porated and the labelling pattern is presumably the same as lanosterol (73) with [2- C,3R,5R- H]mevalonic acid. When [2- C,3R,4R- H]mevalonic acid is fed, six tritium atoms are incorporated [see (75)]. The extra tritium atom is as expected at Cyclo-... 

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