Biosynthetic mechanism

Biosynthetic Mechanism. Riboflavin is produced by many microorganisms, m( dtm. A.shhyagossjpii A.sperigiUus sp remothecium ashbyii Candida yeasts, Debaryomjces yeasts, Hansenu/a yeasts, Picbia yeasts, A. tobactor sp, Clostridium sp, and Bacillus sp. 

Covalently Bound Flavins. The FAD prosthetic group in mammalian succinate dehydrogenase was found to be covalently affixed to protein at the 8 a-position through the linkage of 3-position of histidine (102,103). Since then, several covalently bound riboflavins (104,105) have been found successively from the en2ymes Hsted in Table 3. The biosynthetic mechanism, however, has not been clarified. 

No biosynthetic experiments have been reported for these compounds, but they probably all share the same biosynthetic mechanism. One possibility is that they are generated by cyclization of an a-amino-p-keto carboxyl intermediate that would arise from threonine (136) and sphingosine (131) for 139 and 130, respectively (Figure 11.23). Alternatively, cyclization may precede oxidation, with an aziridine intermediate being formed. 

The biosynthesis of two major classes of red tide toxins, saxitoxin analogs and brevetoxins, have been studied. It was shown that saxitoxin is biosynthesized from arginine, acetate, and methionine methyl group. Brevetoxins were shown to be unique polyketides, which are probably biosynthesized from dicarboxylic acids. Some details of the biosynthetic mechanism have been elucidated. 

In order to obtain more insights into the biosynthetic mechanism, [Me- C-Me-d ] double-labeled methionine was fed to the organism. The C-NMR spectrum of resulting neosaxitoxin showed a clean triplet for C-13 beside the natural abundance singlet. The result indicated that only one deuterium was left on the methylene carbon. 

In this review we fitcus on the biosynthetic mechanisms by vririch the methyl-esterification of the galacturonan chains in pectins is controlled. We go on to examine the structure of the pectic gels that are formed and their relationsh with the stresses carried by specific parts of the cell wall. 

Lipmann, F. Biosynthetic Mechanisms. Harvey Lect., Ser. XLIV 1949, 99. 

Green, D.E. Gibson, D.M. (1960). Fatty acid oxidation and synthesis. In Metabolic Pathways (Greenberg, D.M. Ed.) Vol. I, pp. 301-340. Academic Press, New York. Lipmann, F. (1948-1949). Biosynthetic Mechanisms. Harvey Lectures XLIV, 99-123. Vagelos, P.R. (1964). Lipid metabolism. Annu. Rev. Biochem. 33, 139-172. 

In parallel to the preparative purpose, this research has led to studies of the biosynthetic mechanisms or the cell functions of some amino acids. 

These studies have much contributed to deepen our understanding of the biosynthetic mechanisms for polyketide production, particularly with the fundamental discovery of a novel RppA chalcone-synthase-related enzyme in bacteria (Funa 1999). 

Although it has long been thought, based on genetic mutant and biochemical evidence, that aurones are derived from chalcones, the biosynthetic mechanism has only recently been clarified, and some aspects of the enzymatic process still await in vivo proof An mRNA from A. majns, specifically expressed in the petal epidermal cells, has been shown to encode a recombinant protein with aureusidin synthase (AUS) activity.AUS is a variant polyphenol oxidase (PPO) that can catalyze conversion of either 2, 4, 6, 4-etrahydroxychalcone (naringenin chalcone) or 2, 4, 6, 3,4-pentahydroxychalcone to... 

Pont Lezica355 speculated that the role of dolichyl phosphates, a-satu-rated polyisoprenyl phosphates of chain length between 80 and 105 carbon atoms, in glycosyl transfer during biosynthetic mechanisms is a general feature of eukaryotic cells, whereas, in prokaryotic cells, the lipids fulfilling this function are a-saturated polyisoprenyl phosphates of shorter chain-length, such as undecaprenyl phosphate (which contains 55 carbon atoms). 

It seemed of interest to check whether the type of biosynthetic mechanism involved may be related to the structure of the polymeric chain formed. In the block mechanism of chain assembly, formation of polyprenyl glycosyl diphosphates through transfer of glycosyl phosphate is a necessary step of the process. Thus far, only UDP-activated monosaccharides have been found to participate in this reaction (see Section 11,3). Consequently, the presence of a monosaccharide residue of this group in the main chain of a polymer may be regarded as a necessary condition for assembly of the chain through the block mechanism. 

The biosynthetic mechanisms of secondary products are probably of physiological significance based on ecological demands. 

Gawlitzek M, Valley U, Wagner R (2000), Ammonium alters N-glycan structures of recombinant TNFR-IgG degradative versus biosynthetic mechanisms. Biotechnol. Bioeng. 68 637-646. 

Ken s geographical transition to the New World was accompanied by a concomitant transition in his research emphasis. Although he maintained an interest in polysaccharide chemistry, the publication record from Queen s University attests to the universality of his interests in carbohydrate chemistry. J. K. made major contributions to synthetic carbohydrate chemistry, stereochemistry, biosynthetic mechanisms, and metabolism of carbohydrates, and the application of such separational techniques as paper and gas-liquid chromatography in the carbohydrate field. The results of his lifetime of research were documented in over 300 scientific publications. Clearly, it would be impractical to review this number of papers individually, and consequently, only a representative sample will be treated. A list of Professor Jones s publications is appended to this article. 

Carbamoyl phosphate synthetase is a rate-controlling step in the pyrimidine biosynthetic mechanism. It is inhibited by UTP and other pyrimidine nucleotides. 

The mechanism of penicillin biosynthesis from the Arnstein tripeptide, 8-(L-a-aminoadipoyl)-L-cysteinyl-D-valine (ACV), has been extensively studied and reviewed by many chemists. Most of the biosynthetic mechanisms have been ascertained by Baldwin and Bradley using an excellent enzymatic technique.55 However, the first step in the biosynthesis of penicillin, conversion of the Arnstein tripeptide to a cis-P-lactam intermediate, is still a fascinating mechanistic problem. Although Baldwin et al. recently proposed a mechanism involving an iron-bound thioaldehyde formation route via a Pummerer-type cyclization, the intermediate for this mechanism has not been identified. The mechanism of selective formation of the cw-P-lactam ring is still also unknown (Fig. 39).56 These types of biomimetic reactions have been chemically studied. An example of an unsuccessful intramolecular Pummerer cyclization of the sulfoxide involving a cysteine moiety under standard Pummerer conditions was reported by Wolfe et al.57 Although Kaneko reported the conversion of the very simple 3-phenylsulfinyl propionamide into a P-lactam with TMSOTf/triethylamine,58 a successful biomimetic synthesis of... 

Figure 23 Putative biosynthetic mechanism from versicolorin A to demethylsterigmatocystin.

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