Biosynthetic pathways characterization

Li, Z.H. et ah. Cloning and characterization of a maize cDNA encoding phytoene desaturase, an enzyme of the carotenoid biosynthetic pathway. Plant Mol. Biol. 30, 269, 1996. 

Wildlife toxicologists should be attuned to developments in human health mercury, as assays that have been used successfully on humans may be suitable or adaptable for other vertebrate species. Echeverria and co-workers (Echeverria et al. 2005, 2006 Heyer et al. 2006) have characterized a gene encoding coproporphyrinogen oxidase, a gene in the heme biosynthetic pathway. Polymorphism in this gene predicts differential response to elemental mercury exposure in human subjects. Plans to modify this assay for other mercury species in matrices from wildlife are under way. 

The chain shortening pathway has not been characterized in detail at the enzymatic level in insects. It presumably is similar to the characterized pathway as it occurs in vertebrates. These enzymes are a partial P-oxidation pathway located in peroxisomes [29]. The key enzymes involved are an acyl-CoA oxidase (a multifunctional protein containing enoyl-CoA hydratase and 3-hy-droxyacyl-CoA dehydrogenase activities) and a 3-oxoacyl-CoA thiolase [30]. These enzymes act in concert to chain shorten acyl-CoAs by removing an acetyl group. A considerable amount of evidence in a number of moths has accumulated to indicate that limited chain shortening occurs in a variety of pheromone biosynthetic pathways. 

In this discussion, we have restricted ourselves to the consideration of only a few examples of arthropod chemistry. From these alone, it is evident that insects synthesize defensive compounds by using all of the major biosynthetic pathways, producing acetogenins, simple aromatics and quinones, isoprenoids, and alkaloids. In addition, some of the millipedes, coccinellid beetles, and spiders we have studied utilize biosynthetic pathways that have yet to be characterized. 

Sofia HJ, Chen G, Hetzler BG, et al. 2001. Radical SAM, a novel protein superfanuly linking unresolved steps in familiar biosynthetic pathways with radical mechanisms functional characterization using new analysis and information visualization methods. Nucleic Acids Res 29 1097-106. 

Yeast isopropylmalate isomerase of the leucine biosynthetic pathway, which catalyzes a totally analogous reaction to that of aconitase, converts 3-hydroxy-3-carboxy-4-methylpentanoate to 2-hydroxy-3-carboxy-4-methylpentanoate via an allylic intermediate. In its initial characterization by EPR spectroscopy, a high-field shift in its EPR signal from a g-average of 1.96 to 1.90 is seen upon addition of substrate (70). This result suggests that its mechanism is the same as that found for aconitase. 

Uefuji, H., Ogita, S., Yamaguchi, Y Koizumi, N. and Sano, H. 2003. Molecular cloning and characterization of three distinct N-methyltransferases involved in the caffeine biosynthetic pathway in coffee plants. Plant Physiology, 132(1) 372-380. 

There are many branches to the flavonoid biosynthetic pathways, with the best characterized being those leading to the colored anthocyanins and proanthocyanidins (PAs) and the generally colorless flavones, flavonols, and isoflavonoids. Genes or cDNAs have now been identified for all the core steps leading to anthocyanin, flavone, and flavonol formation, as well as many steps of the isoflavonoid branch, allowing extensive analysis of the encoded enzymes (Table 3.1). In addition, several DNA sequences are available for the modification enzymes that produce the variety of structures known within each class of compound. 

The farinose exudate of the frond of the fern Pityrogramma calomelanos (Adiantaceae) has been the source of complex flavonoids characterized by a novel Ce-Cs-Ce-Cs-Ce skeleton (Table 15.7). This group includes four flavanones, calomelanols G (238), H (239), I (240), and J (241) (Figure 15.10). In these compounds, a molecule of p-coumaric or cinnamic acid appears to be fused with the A-ring of the flavanone. Biosynthetic pathways for these complex flavanones and related flavones, chalcones, and dihydrochalcones in P. calomelanos and other Pityrogramma species have been proposed by the authors. 

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