Biosynthesis primer

Capsaicinoids are synthesized by the condensation of vanillylamine with a short chain branched fatty acyl CoA. A schematic of this pathway is presented in Fig. 8.4. Evidence to support this pathway includes radiotracer studies, determination of enzyme activities, and the abundance of intermediates as a function of fruit development [51, 52, 57-63], Differential expression approaches have been used to isolate cDNA forms of biosynthetic genes [64-66], As this approach worked to corroborate several steps on the pathway, Mazourek et al. [67] used Arabidopsis sequences to design primers to clone the missing steps from a cDNA library. They have expanded the schema to include the biosynthesis of the key precursors phenylalanine and leucine, valine and isoleucine. Prior to this study it was not clear how the vanillin was produced, and thus the identification of candidate transcripts on the lignin pathway for the conversion of coumarate to feruloyl-CoA and the subsequent conversion to vanillin provide key tools to further test this proposed pathway. 

FIGURE 3.1 Development of PCR-based detection systems for mycotoxin producing-fungi from 1996 until April 2007. First publication of a diagnostic primer pair was taken as the time mark for each species depicted. In many cases, more systems were published later for the same fungus. Mycotoxin biosynthesis genes used as sequence source are given in bold. 

C. Trichothecene biosynthesis cluster genes as sequence source for primer design... 

Rubber is synthesized and sequestered on cytsolic vesicles known as rubber particles. Rubber transferase is localized to the surface of the rubber particles, and biosynthesis is initiated through the binding of an allylic pyrophosphate (APP, a pyrophosphate, produced by soluble trans- rtnyl transferases) primer. Progressive additions of IPP molecules ultimately result in the formation of high molecular weight cjT-l,4-polyisoprene. The rubber transferase also requires a divalent cation, such as Mg + or Mn +, as cofactor. 

All rubber transferases exhibit similar kinetic constants and pH optima, and are able to accept a similar range of APPs as initiating substrate [263, 264], In vitro studies have shown that several compounds (DMAPP, GPP, FPP, and GGPP) can initiate rubber biosynthesis, with a faster rate of rubber biosynthesis the longer the APP (up to C15 or C20) [254, 265], Non-natural APPs were also shown to be able to function as a primer for the rubber biosynthesis [266],... 

Mann J (1994) Chemical Aspects of Biosynthesis. Oxford Chemistry Primers, Oxford. 

In 1967, two possible general mechanisms for the biosynthesis of linear polysaccharides were proposed.86 The first was the primer mechanism already discussed, and the second was the sequential addition of monomer units to the reducing end by the insertion between a carrier and the growing polysaccharide chain. This latter mechanism had been shown for Salmonella sp. O-antigenic polysaccharide87 then in 1973, it was shown for the bacterial cell-wall polysaccharide murein88 in which the carrier was a polyisoprenoid pyrophosphate. 

Because the reaction is degradative, it requires a starch chain, and the product of a single event is a-Glc 1-P and a starch chain that has had one or more glucosyl residues removed. It is, therefore, not surprising that the reaction in the reverse synthetic direction also requires a starch chain or so-called primer. The primer hypothesis for the synthesis of polysaccharide was, thus, developed from an enzyme that was actually a degradative enzyme and not a synthetic enzyme. Nevertheless, the primer-dependent mechanism has been incorrectly assumed for the biosynthesis of starch for over 60 years. 

Lomako, J., Lomako, W. M., and Whelan, W. J. 1988. A self-glucosylating protein is the primer for rabbit muscle glycogen biosynthesis. FASEB. J. 2, 3097-3103. 

Primer Unit Engineering and Precursor-Directed Biosynthesis... 

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