Chain length specificity

FIGURE 24.15 The conversion of trans- and m-enoyl CoA derivatives to l- and d-/3-hydroxyacyl CoA, respectively. These reactions are catalyzed by enoyl-CoA hydratases (also called crotonases), enzymes that vary in their acyl-chain length specificity. A recently discovered enzyme converts ram-enoyl-CoA directly to D-/3-hydroxyacyl-CoA. 

Although it could be established that saturation of the a-isoprene unit of polyprenol phosphate is important for these compounds to act as effective acceptors of glycosyl moieties in eukaryotic cells, little chain-length specificity was observed in such studies.39-41 This observation found support in the result that the same set of prenylogs occurs in total-yeast dolichol and in dolichol diphosphate-linked 2-acetamido-2-deoxy-D-glucose synthesized in vitro with yeast-cell homogenates.42 As already noted by Chojnacki and coworkers,40 dur-... 

After drying and delipidation this biomass can be considered as a naturally immobilized enzyme (Fig, 3.). The hydrolytic activity measured on olive oil in di-isopropyl-ether is around 75 to 200 micromoles per g of dry mycelium and per mn. The chain length specificity spectrum is broad, as shown before (from C14 to C22). 

Vaz A. H., Jurenka R. A., Blomquist G. J. and Reitz R. C. (1988) Tissue and chain length specificity of the fatty acyl-CoA elongation system in the American cockroach. Arch. Biochem. Biophys. 267, 551-557. 

Figure 8.3 Steps in fatty acyl-CoA elongation condensation, reduction, dehydration and reduction. The condensation step appears to regulate chain length specificity.

The regulation of the chain length specificity to produce the specific blend of hydrocarbons often used in chemical communication appears to reside in the microsomal fatty acyl-CoA elongase reaction and not in the reductive conversion of fatty acyl-CoAs to hydrocarbon. The American cockroach produces three major hydrocarbons n-pentacosane, 3-methylpentacosane and (Z,Z)-9,12-heptacosadiene (Jackson, 1972). Studies with microsomes from integument tissue showed that stearyl-CoA was elongated up to a 26 carbon acyl-CoA that could serve as the precursor to n-pentacosane. In contrast, linoleoyl-CoA... 

Franco, V.A., Liu, D., Reeves, P.R. The Wzz (Cld) protein in Escherichia coli amino acid sequence variation determines O antigen chain length specificity. J Bacteriol 180 (1998) 2670-2675. 

All C9-reduced polyketides first undergo cyclization between Cl and Cl2. The reduced ring is unable to aromatize in the absence of additional enzymes, as seen in the structures of mutactin, RM20b and RM20c. Introduction of chain-length-specific... 

Croteau, R. and Purkett, P.T. (1989) Geranyl pyrophosphate synthase characterization of the enzyme and evidence that this chain-length specific prenyltransferase is associated with monoterpene biosynthesis in sage (Salvia officinalis). Arch. Biochem. Biophys., 271,524—35. 

Using stereospecifically tritiated NADPH enantiomers, it was demonstrated that only tritium from the [4- Hsi]NADPH is incorporated into 6-MSA [32]. Presumably, the ketoreductase possesses stereospecificity for the Hs of the dihydronicotinamide ring of NADPH and chain length specificity for the six-carbon ketide intermediate. 

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