Keto acyl synthase

These chain lengths may be maintained by the combined action of the three keto-acyl synthase enzymes (KAS I-III), and relatively specific thioesterases that convert acyl-ACP molecules to the corresponding CoA derivatives. Most plants have an acyl-ACP thioesterase with the highest activity for oleyl-ACP. Chain termination also may occur when fatty acids are transferred from ACP to glycerol-3-phosphate by acyltransferases (Ohlrogge et al., 1993) (see below). 

Harington A, Herbert CJ, Tung B, Getz GS, Slo-nimski PP. Identification of a new nuclear gene (CEMl) encoding a protein homologous to a P-keto-acyl synthase which is essential for mitochondrial respiration in Saccharomyces cerevisae. Mol Microbiol. 1993 9 545-55. 

Figure 3.8 One complete cycle and the first step in the next cycle of the events during the synthesis of fatty acids. ACP = acyl carrier protein, a complex of six enzymes i.e. acetyl CoA-ACP transacetylase (AT) malonyl CoA-ACP transferase (MT) /3-keto-ACP synthase (KS) /J-ketoacyl-ACP reductase (KR) / - hydroxyacyl-ACP-dehydrase (HD) enoyl-ACP reductase (ER).

J-A Chuck, M McPherson, H Huang, JR Jacobsen, C Khosla, DE Cane. Molecular recognition of diketide substrates by a P-keto-acyl carrier protein synthase domain within a bimodular polyketide synthase. Chem Biol 4 757-766, 1997. 

During the first reaction on fatty acid synthase, acetyl transacylase catalyzes the transfer of the acetyl group from an acetyl-CoA molecule to the SH group of a cysteinyl residue of /J-ketoacyl-ACP synthase. Malonyl-ACP is formed when malonyl transacylase transfers a malonyl group from malonyl-CoA to the SH group of the pantetheine prosthetic group of ACP (reaction 2). Then /J-keto-acyl-ACP synthase catalyzes a condensation reaction (reaction 3) in which ace-toacetyl-ACP is formed (Figure 12.14). 

Fig. 2 Metabolic routes for mcl-PHA biosynthesis. Pseudomonas putida GPol synthesizes PHA through P-oxidation and P. putida KT2440 synthesizes PHA through fatty add de novo synthesis. Special PHA consisting of 4-hydroxyalkanoate, 5- hydroxyalkanoate, or 6-hydroxyalkanoate can be produced by various bacteria when suitable precursors are supplied. 1 acyl-CoA synthetase, 2 acyl-CoA dehydrogenase, 3 enoyl-CoA hydratase, 4 NAD-dependent (5)-3-hydroxyacyl-CoA dehydrogenase, 5 3-ketoacyl-CoA thiolase, 6 (ItFspecific enoyl-CoA hydratase, 7 NADPH-dependent 3-ketoacyl-CoA reducatase, 8 3-hydroxyacyl-CoA epimerase, 9 mcl-PHA polymerase, 10 acetyl-CoA carboxylase, 11 malonyl-CoA-acyl carrier protein (ACP) tiansacylase, 12 3-keto-ACP synthase, 13 3-keto-ACP reductase, 14 3-hydroxyacyl-ACP dehydratase, 15 enoyl-ACP reductase, 16 acyl-ACP thiolase, 17 (l )-3-hydroxyacyl-ACP-CoA transacylase, 18 mcl-PHA polymerase...

CAN E. COLI p-HYDROXYDECANOYL-ACP DEHYDRASE AND P-KETO-ACYL-ACP SYNTHASE I INTERACT WITH BRASSICA NAPUS FATTY ACID SYNTHASE TO ALTER OIL SEED COMPOSITION ... 

Can E.coli p-Hydroxydecanoyl-ACP Dehydrase and P-Keto-Acyl-ACP Synthase I Interact with Brassica napus Fatty Acid Synthase to Alter Oil Seed Composition ... 

Our studies on fatty acid synthesis in the oil palm mesocarp have indicated that the enzymes acyl AGP thioesterase and beta-keto acyl AGP synthase II control the levels of palmitate and oleate. Thioesterase activity in the crude extract showed a marked preference for palmitoyl AGP [3]. Anion exchange chromatography (HR DEAE) resulted in the resolution of two peaks, one showing a marked preference for palmitoyl AGP and the other for oleoyl AGP. Both peaks were further purified using hydroxyapatite chromatography followed by AGP Sepharose... 

The enzyme beta-keto acyl AGP synthase II was purified more than 10,000-fold. The activity of the enzyme in the mesocarp correlates positively with the level of unsaturation of the fatty acids present in the crude oil extract. Activity of synthase II increased with fruit ripening, reaching a maximum at 20 weeks after anthesis. The results of these investigations suggest that high levels of palmitate in palm oil is likely to be due to low synthase II activity and the specificity of the thioesterase for palmitoyl AGP. 

Malonyl-CoA Keto-acyl-CoA synthase NADPE1 i p-Ketoacyl-CoA reductase... 

FIGURE 25.25 Biosynthesis of sphingolipids in animals begins with the 3-ketosphinga-nine synthase reaction, a PLP-dependent condensation of palmitoyl-CoA and serine. Subsequent rednction of the keto group, acylation, and desatnration (via rednction of an electron acceptor, X) form ceramide, the precnrsor of other sphingolipids. 

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