Anabolic synthase

Scheme 2.2.5.23 Alternative pathways for sialic acid synthesis using the catabolic aldolase (NeuA) or the anabolic synthase (NeuS) enzymes.

The availability of both the cataboHc aldolase and the uniquely synthetic anabolic synthase made it possible to assemble a novel continuous assay for the determination of the metabolite N-acetylneuraminic acid [46]. A combination of both enzymes, in the presence of an excess of PEP, will start a cycle in which the determinant sialic acid will undergo a steady conversion of cleavage and re-syn-thesis as a futile cycle (Scheme 2.2.5.24). With each progression, however, 1 equiv of pyruvate is liberated simultaneously, which causes time-dependent signal amplification. Pyruvate is quantified spectrophotometrically by a corresponding NADH consumption when the system is coupled to the standard pyruvate dehy-... 

Fig. 14.3 5 -FU catabolism, anabolism and mechanism of action. 5-FUH2, 5-fluoro-5,6-dihydrouracil 5-FdUMP, 5-fluorodeoxyuridine monophosphate TP, thymidine phosphorylase TK, thymidine kinase TS, thymidylate synthase CH2THF, 5,10-methylenetetrahydrofolate.

In 1995, Horie et al. described a polymorphic tandem repeat found in the 5 -un-translated region of the thymidylate synthase gene [70]. Thymidylate synthase (TS TYMS) catalyzes the intracellular transfer of a methyl group to deoxyuridine-5-monophosphate (dUMP) to form deoxythymidine-5-monophosphate (dTMP), which is anabolized in cells to the triphosphate (dTTP). This pathway is the only de- novo source of thymidine, an essential precursor for DNA synthesis and repair. The methyl donor for this reaction is the folate cofactor 5,10-methylenetetrahydro-folate (CH2-THF) (Figure 24.4). 

Fig. lA. Anabolic and catabolic pathways of 5-FU. DPD dihydropyrimidine dehydrogenase, DP di-hydropyrimidinase, pUP beta-ureidopropionase, UP uridine phosphorylase, OPRT orotate phospho-ribosyl transferase, UK uridine kinase, TP thymidine phosphorylase, TK thymidine kinase, RNR ribonucleotide reductase. The three active metabolites (shown in rectangles) are FdUMP (5-fluoro-2 -deoxyuridine 5 -monophosphate) inhibiting TS (thymidylate synthase), and FUTP (5-fluorouridine 5 -triphosphate) and FdUTP (5-fluoro 2 -deoxyuridine 5 -triphosphate) interfering with RNA and DNA, respectively. 

Figure 7-1. Pathways of fuel metabolism and oxidative phosphorylation. Pyruvate may be reduced to lactate in the cytoplasm or may be transported into the mitochondria for anabolic reactions, such as gluconeogenesis, or for oxidation to acetyl-CoA by the pyruvate dehydrogenase complex (PDC). Long-chain fatty acids are transported into mitochondria, where they undergo [ -oxidation to ketone bodies (liver) or to acetyl-CoA (liver and other tissues). Reducing equivalents (NADH, FADII2) are generated by reactions catalyzed by the PDC and the tricarboxylic acid (TCA) cycle and donate electrons (e ) that enter the respiratory chain at NADH ubiquinone oxidoreductase (Complex 0 or at succinate ubiquinone oxidoreductase (Complex ID- Cytochrome c oxidase (Complex IV) catalyzes the reduction of molecular oxygen to water, and ATP synthase (Complex V) generates ATP fromADP Reprinted with permission from Stacpoole et al. (1997).

Additionally, the study demonstrated that there are fatty acid metabolism genes that were positively associated with lovastatin production and tended to encode catabolic enzymes that are predicted to promote formation of the polyketide precursors acetyl-CoA and malonyl-CoA, whereas fatty acid metabolism genes that are negatively associated with secondary metabolite production encode anabolic enzymes, i.e., acyl-CoA oxidase, fatty acid desaturase, and fatty acid synthases. 

Activated PKB (Akt) phosphorylates the following proteins with the indicated anabolic consequences Bad phosphorylation yields P-Bad which then dissociates from a Bcl-2-Bcl-X] complex in the mitochondrial outer membrane and is sequestered by 14.3.3 proteins. Mitochondrial pore blockage by the Bad-free Bcl-2-Bcl-xL complex successively prevents cytochrome c release from mitochondria, blocks procaspase activation by cytochrome c and thus inhibits apoptosis and increases cell survival. Phosphorylation of p70S6 kinase by PKB results in activation of this PK, phosphorylation of ribosomal small subunit protein S6 and enhancement of translation (protein synthesis). Phosphorylation of glycogen synthase (GS) kinase 3 (GSK3) by PKB results in an inactive P-GSK3, a consequent increase in the amount of the active non-phosphorylated form of GS and increased glycogen synthesis. 

Alanine Cycle, 437 Albuminoids, 150 Albumins, 149 Aldolase, 282 Aldonic Acids, 53 Aldoses, 48 Allosterism, 166 Amino Acid Oxidase, 433 Amino Acids, 139, 294 Amino Sugars, 52 Amino transferases, 431 Amylopectin, 58 Amylose, 58 Anabolism, 257 Antibiotics, 450 Apoenzymes, 184 ATP Synthase, 315, 478 Autotrophs, 475... 

Interestingly, POX has a genetically closely related cousin acetolactate synthase" (ALS) that still has a bound FAD. Instead of oxidizing the enamine, ALS employs the enamine in nucleophilic addition to a second pyruvate producing acetolactate, an important anabolic intermediate in the biosynthesis of the essential aliphatic amino acids in plants. ALS is a major target for herbicides . ALS may be using the FAD to protect the enamine from being protonated, prior to condensation. 

Fig. 13. Metabolism scheme of sialic acids. Anabolic (solid arrow) and catabolic (dashed arrow) reactions are indicated. For literature see the text. Enzymes 1, CMP-sialate synthase (EC 2.7.7.43) 2, sialyltransferases (EC 2.4.99.1.) 3, CMP-Neu5Ac hydroxylase (EC 1.14.99.18) 4, acetyl-CoA sialate 4-0-acetyltransferase (EC 2.3.1.44) 5, acetyl-CoA sialate 7(9)-0-acetyltransferase (EC 2.3.1.45) 6,. S-adenosyl-L-methionine sialate 8-O-methyltransferase (proposed EC 2.1.1.78) 7, sialate 4- or 9-0-acetylesterases (EC 3.1.1.53) 8, sialidase (EC 3.2.1.18) 9, sialate-pyruvate lyase (aldolase EC 4.1.3.3). Both Neu5Ac and Neu5Gc can be O-acetylated by the two O-acetyltransferases. There may also exist a sulfotransferase, since sulfated sialic acids have been found in e.g. echinoderms [13,577]. ( ), Sialic-acid-accepting nascent glycoconjugate.

The glycolytic pathway includes three such reactions glucose 6-phosphate isomer-ase (1,2-proton transfer), triose phosphate isomerase (1,2-proton transfer), and eno-lase (yS-elimination/dehydration). The tricarboxylic acid cycle includes four citrate synthase (Claisen condensation), aconitase (j5-elimination/dehydration followed by yS-addition/hydration), succinate dehydrogenase (hydride transfer initiated by a-proton abstraction), and fumarase (j5-elimination/dehydration). Many more reactions are found in diverse catabolic and anabolic pathways. Some enzyme-catalyzed proton abstraction reactions are facilitated by organic cofactors, e.g., pyridoxal phosphate-dependent enzymes such as amino acid racemases and transaminases and flavin cofactor-dependent enzymes such as acyl-C-A dehydrogenases others. 

Waxes are long-chain fatty alcohols esterified to long-chain fatty acids and constitute the second anabolic use of long-chain fatty alcohols. Waxes coat environmentally exposed surfaces of mammals, insects, and plants forming a slippery, water impervious barrier. A wax synthase gene has now been cloned from a mouse preputial gland and is present in other glands associated with wax production (Section 7.1.1). The enzyme has a broad fatty alcohol and fatty acid substrate preference, yet does not employ acceptors other than fatty acids. 

It is more likely that hyaluronic acid viscosupplementation produees its effects through down-regulation of aggrecanse-2, tumor necrosis factor alpha (TNF alpha), interleukin-8 (IL-8), inducible nitric oxide synthase (iNOS), and matrix metalloproteinases leading to anti-inflammatory, anabolic and analgesic effects, or through an interaction between hyaluronic acid and cell receptor CD44 [83, 95, 105, 113]. 

Chiral R-form hydroxyalkanoic acids are normally difficult to synthesize by chemical means. The occurrence of over 120 different chiral R-forms of PHA monomers reflects the low substrate specificity of PHA synthases, which are the key enzymes of PHA biosynthesis [7, 8, 22], These can be used as a rich pool of chrial compounds [13]. In addition, the importance of bacterial anabolism and catabolism, which provide the coenzyme A thioesters of the respective monomers as substrates to these PHA synthases, is also important in controlling the structure of hydroxyalkanoic acids [23]. 

Three enzymes are involved in the synthesis of 2,3-BD a-acetolactate synthase (EC 4.1.3.18), a-acetolactate decarboxylase (EC 4.1.1.5), and butanediol dehydrogenase (also known as diacetyl [acetoin] reductase Larsen and Stormer 1973 Johansen et al. 1975 Stormer 1975). Two different enzymes form acetolactate from pyruvate. The first, termed catabolic a-acetolactate synthase, has a pH optimum of 5.8 in acetate and is part of the butanediol pathway. The other enzyme, termed anabolic a-acetolactate synthase or acetohydroxyacid synthetase, has been well studied and characterized and will not be discussed here. This enzyme is part of the biosynthetic pathway for isoleucine, leucine, and valine and is coded for by the ilvBN, ilvGM, and ilvH genes in E. colt and Salmonella typhimurium (Bryn and Stormer 1976). 

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