Origin biosynthesis

Related to the long-chain fatty adds, several linear derivatives with very long chains (n-G37-n-C39), olefinic hydrocarbons, methylketones and esters, were charader-ized in the species Emiliania huxieyi, for instance in sediments of the Quaternary period. For the unsaturated derivatives, it was established by synthesis that all the double bonds had the configuration ( ), suggesting original biosynthesis mechanisms (Volkman et al., 1980,1998 ... 

De mvo biosynthesis of the two acylated Cio parts of triophamine occurs through a mechanism of the polyke-tide type from two butyrate units and an acetate unit, as has been demonstrated by direct injection into the mollusk of [2,3- C2] butyrate. This forms an intermediate, mono-ethylmalonate, the condensation of which with guanidine leads to triophamine (Kubanek and Andersen, 1997). Incorporating [2,3- C2] monoefhylmalonate confirms the results of the incorporation of butyrate despite a very low incorporation rate. The steps in this original biosynthesis are shovm in Figure 23.27. 

The enzyme catalyzed reactions that lead to geraniol and farnesol (as their pyrophosphate esters) are mechanistically related to the acid catalyzed dimerization of alkenes discussed m Section 6 21 The reaction of an allylic pyrophosphate or a carbo cation with a source of rr electrons is a recurring theme m terpene biosynthesis and is invoked to explain the origin of more complicated structural types Consider for exam pie the formation of cyclic monoterpenes Neryl pyrophosphate formed by an enzyme catalyzed isomerization of the E double bond m geranyl pyrophosphate has the proper geometry to form a six membered ring via intramolecular attack of the double bond on the allylic pyrophosphate unit... 

Isotope incorporation experiments have demonstrated the essential correctness of the scheme presented m this and preceding sections for terpene biosynthesis Considerable effort has been expended toward its detailed elaboration because of the common biosyn thetic origin of terpenes and another class of acetate derived natural products the steroids... 

Once the broad outlines of DNA replication and protein biosynthesis were established scien tists speculated about how these outlines af fected various origins of life scenarios A key question concerned the fact that proteins are re quired for the synthesis of DNA yet the synthesis of these proteins is coded for by DNA Which came first DNA or proteins How could DNA store genetic infor mation if there were no enzymes to catalyze the polymerization of its nucleotide components How could there be proteins if there were no DNA to code for them ... 

The ansa-chain of the ansamycins streptovaricins (4), rifamycins (263), geldanamycin (4), and herbimycin (32) has been shown to be polyketide in origin, being made up of propionate and acetate units with the 0-methyl groups coming from methionine. The remaining aromatic C N portion of the ansamacroHdes is derived from 3-amino-5-hydroxybenzoic acid (264—266) which is formed via shikimate precursors. Based on the precursors of the rifamycins and streptovaricins isolated from mutant bacteria strains, a detailed scheme for the biosynthesis of most of the ansamacroHdes has been proposed (95,263). 

FIGURE 12.1 DNA replication yields two daughter DNA duplexes identical to the parental DNA molecule. Each original strand of the double helix serves as a template, and the sequence of nucleotides in each of these strands is copied to form a new complementary strand by the enzyme DNA polymerase. By this process, biosynthesis yields two daughter DNA duplexes from the parental double helix. 

These tautomerization experiments have also been performed with uroporphyrinogens,25e 24 which are important intermediates in the biosynthesis of natural porphinoids and corrinoids. This has led to a deeper insight into biosynthetic pathways and a possible prebiotic origin of... 

The acetate labeling results clearly demonstrated a polyketide origin for the naphthoate fragment. This resulted in the hypothesis that the first enzyme-free intermediate in azinomycin biosynthesis would be naphthoate 102, with condensation to fonn a polyketone chain, reduction, cyclization, and dehydration/aromati-... 

Anabolism is the building up or biosynthesis, of complex molecules such as protein, nucleic adds and polysaccharides, from raw materials originating from intra- or extracellular sources. The biosyntheses are energy (ATP) requiring processes. 

Much less is known about the participation of sugars in the biosynthesis of pyramine in yeasts, and although it has been proven that sugars can provide some carbon atoms, the exact nature of the more advanced intermediates of sugar origin is not yet clear. Some features of the biosynthesis in S. cerevisiae are summarized in Scheme 33. Two l5N atoms from DL-(l,3-,5N2)histidine were incorporated into the N-3 and amino nitrogen atoms of pyramine. The nitrogen atom of (,5N)aspartate, a known precursor of N-l of histidine, was incorporated into pyramine without dilution.58-70 It was also found that N-l and C-2 of pyramine came respectively from N-l and C-2 of pyridoxol.71-73... 

Part of the diet consists of fats, which are triglycerol esters of fatty acids (FAs). The FAs from digestion of ingested fats can be metabolized in a variety of pathways. Fragments of the original FAs are preserved in these processes and can be utilized in the biosynthesis of other molecules. It is important to note that, during metabolism, almost all FAs are broken down into two-carbon units. The only exceptions are FAs with odd numbers of carbon atoms these are relatively rare in the diet. It ean be shown further that there is a partial barrier to the incorporation of FA-derived carbon into the amino acids which constitute collagen. 

The estrogens are a family of hormones synthesized in a variety of tissues. 17P-Estradiol is the primary estrogen of ovarian origin. In some species, estrone, synthesized in numerous tissues, is more abundant. In pregnancy, relatively more estriol is produced, and this comes from the placenta. The general pathway and the subcellular localization of the enzymes involved in the early steps of estradiol synthesis are the same as those involved in androgen biosynthesis. Features unique to the ovary are illustrated in Figure 42-7. 

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