Acetoacetyl-coenzyme A reductase

In another study by Dennis and co-workers [41], the PHA accumulation of several microorganisms Escherichia coli, Klebsiella aerogenes and PHA-negative mutants of Cupriavidus necator and Pseudomonas putida) that expressed the phaC and acetoacetyl-coenzyme A reductase phaB) of Cupriavidus necator were analysed. This results in a construct that puts phaC and phaB under the control of the original Cupriavidus necator promoter. It was found that wild-type Cupriavidus necator was able to produce sc/-PHA, however the recombinant Cupriavidus necator expressing its own phaC and phaB without P-ketothiolase phaA) were able to accumulate poly(3HB-co-3HHx) when cultivated with even number chain fatty acids. The same trend was reported for Klebsiella aerogenes and Pseudomonas putida. 

Brigham CJ, Kurosawa K, Rha CK, Sinskey AJ (2011) Bacterial carbon storage to value added products. J Microbial Biochem Technol 83 83-002 Brigham CJ, Gai CS Lu J, Speth DR, Worden RM, Sinskey AJ (2012) Engineering Ralstonia eutwpha for production of isobutanol from CO, H, and Oy In Lee JW (ed) Advanced biofuels and bioproducts. Springer, New York, DOI 10.1007/978-l-4614-3348-4 39 Bruland N, Voss I, Bramer C, Steinbtichel A (2009) Unravelling the C(3)/C(4) carbon metabolism in Ralstonia eutropha H16. J Appl Microbiol 109 79-90 Budde CF, Mahan AE, Lu J, RhaC, Sinskey AJ (2010) Roles of multiple acetoacetyl coenzyme A reductases in polyhydroxybutyrate biosynthesis in Ralstonia eutropha H16. J Bacteriol 192 5319-5328... 

Taroncher-Oldenburg G, Nishia K, Stephanopoulos G (2000) Identification and analysis of polyhydroxyalkanoate-specific P-ketothiola e and acetoacetyl coenzyme A reductase genes in cyanobacterium Synechocystis p. strain PCC6803. Appl Environ Microbiol 66 4440-4448 Thauer RK (1989) Biochemistry of acetic acid metabolism in anaerobic chemotropic bacteria. Ann Rev Microbiol 43 43-67 Toda K, Park YS, Asakura T, Cheng CY, Ohtake H (1989) High rate acetic acid production in a shallow flow bioreactor. Appl Microbiol Biotechnol 30 559-563 Tsai SP, Moon S-H (1998) An integrated bioconversion process for the production of L-lactic acid from starchy potato feed stocks. Appl Biochem Biotechnol 70-72 417-428... 

Two types of polyhydroxyalkanoate (PHA) biosynthesis gene loci (phb and pha) of Pseudomonas sp. strain 61-3, which produces a blend of poly-3-hydroxybutyrate [PHB] homopolymer and a random copolymer poly(3-hydroxybutyrate-co-3-hydroxyalkanoate) [P(3HB-co-3HA] consisting of 3HA units of 4 to 12 carbon atoms, were cloned and analyzed at the molecular level [274]. In the phb locus, three open reading frames encoding polyhydroxybutyrate (PHB) synthase (PhbCPs), 6-ketothiolase (PhbAPs), and NADPH-dependent acetoacetyl coenzyme A reductase (PhbBPs) were... 

The incorporation of malonate into mevalonic acid and steroids has been investigated further. Experiments with normal and tumorous rats have demonstrated the previously unsuspected fact that the S-methyl group of methionine is incorporated into cholesterol and cholest-7-en-3jS-ol. Some of the enzymes involved in mevalonate synthesis have been isolated. Yeast acetoacetyl coenzyme A thiolase (EC 2.3.1.9) has a molecular weight of about 190 000 and 3-hydroxy-3-methyl glutaryl coenzyme A synthetase (EC 4.1.3.5) a molecular weight of 130 000. Rat liver 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) used only [4/ - H]NADPH in the formation of mevalonic acid with incorporation of two tritium atoms (at Hp and Hp) (see Scheme 1). 

Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA reductase) converts 3-hydroxy-3-methylglutaryl coenzyme A to mevalonate, a precursor of cholesterol. Human 3-hydroxy-3-methylglutaryl coenzyme A, also abbreviated as HMGR consists of a polypeptide chain of 888 amino acids [9]. Acetyl-CoA condenses with acetoacetyl-CoA to form HMG-CoA reductase. 

Steps 6-8 of Figure 29.5 Reduction and Dehydration The ketone carbonyl group in acetoacetyl ACP is next reduced to the alcohol /S-hydroxybutyry] ACP by yS-keto thioester reductase and NADPH, a reducing coenzyme closely related to NADH. R Stereochemistry results at the newly formed chirality center in the /3-hydroxy thioester product. (Note that the systematic name of a butyryl group is biitanoyl.)... 

Two acetoacyl-CoA reductases were found by Haywood et al. in R. eutropha [cited in 78], each with a distinct substrate and coenzyme (NADH or NADPH) specificity. NADPH-dependent acetoacetyl-CoA reductase mediates the reversible reduction of four- to six-carbon 3-ketoacyl-CoAs to the R isomers only of hydroxyacyl-CoAs. NADH-linked acetoacetyl-CoA reductase effects the oxidation of both R and S substrates to acetoacetyl-CoA, but produces only S-3-hydroxybutyryl-CoA in the reverse reduction reaction. Doi and co-workers [156] have advanced that the reduction of 3-ketoacyl-CoA by the NADPH-dependent reductase may be the rate-determining step in PHA synthesis. 

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