Acetate synthetase

MethylmalonylCoA mutase Glutamate mutase a-Methylene-glutarate mutase Dioldehydrase Glyceroldehydrase Ethanoldeaminase L-/3-lysine mutase D-a-lysine mutase Ribonucleotide reductase Methionine synthetase Methane synthetase Methyl transferase Acetate synthetase... 

Among the enzymes implicated in mercury methylation are methionine synthetase, acetate synthetase, and methane synthetase. The last one is a very common enzyme in anaerobic ecosystems, such as lake and river sediments. These enzymatic processes can generate and CHa species where... 

Fatty acid synthetase (Section 26 3) Complex of enzymes that catalyzes the biosynthesis of fatty acids from acetate Field effect (Section 19 6) An electronic effect in a molecule that IS transmitted from a substituent to a reaction site via the medium (e g solvent)... 

Fatty acid synthetase (Section 26.3) Complex of enzymes that catalyzes the biosynthesis of fatty acids from acetate. 

In this reaction sequence acetic acid synthesis requires methyl transfer as CH3 to a Co(I)-corrin by N2 5-methyltetrahydrofolate monoglutamate to give a methylcorrinoid intermediate which is carboxylated to give a carboxymethylcorrinoid. This carboxymethylcorrinoid would then be reductively removed by NADPH to give acetic acid and regenerate the Co(I)-corrin. In contrast to the methyl-transfer proposed for the methionine synthetase reaction, this mechanism suggests that CH3-stabilized by Co attacks CO2 to give a carboxymethylcorrinoid intermediate. 

Short-chain acyl-CoA synthetase activates short-chain fatty acids, acetic, butyric and propionic acid. The enzyme is present in both the cytosol and in the mitochondrial matrix of most tissues the activity is especially high in the liver and the colon. 

A very high activity of mitochondrial aldehyde dehydrogenases (together with its low ensures very efficient oxidation in the liver so that the concentration of acetaldehyde in blood remains very low. Nonetheless, it is possible that some of the pathological effects of ethanol are due to acetaldehyde (ethanal). In contrast, a large proportion of the acetate escapes from the liver and is converted to acetyl-CoA by acetyl-CoA synthetase in other tissues ... 

ACETATE KINASE ACETYL-CoA CARBOXYLASE ACETYL-CoA SYNTHETASE N-ACETYLCLUCOSAMINE KINASE ACTIN ATPase ACTOMYOSIN ATPase N-ACYLMANNOSAMINE KINASE ADENINE NUCLEOTIDE TRANSLOCASE ADENOSINE KINASE ADENYLATE KINASE (MYOKINASE) ADENYLYLSULFATE KINASE d-ALANINE-d-ALANINE LIGASE... 

Fig. 7. Enzyme-coupled assay in which the hydrolase-catalyzed reaction releases acetic acid. The latter is converted by acetyl-CoA synthetase (ACS) into acetyl-CoA in the presence of (ATP) and coenzyme A (CoA). Citrate synthase (CS) catalyzes the reaction between acetyl-CoA and oxaloacetate to give citrate. The oxaloacetate required for this reaction is formed from L-malate and NAD in the presence of L-malate dehydrogenase (l-MDH). Initial rates of acetic acid formation can thus be determined by the increase in adsorption at 340 nm due to the increase in NADH concentration. Use of optically pure (Ry- or (5)-acetates allows the determination of the apparent enantioselectivity i app i81)-...

For ATP regeneration, a similar concept has been used (Berke et al, 1988). ATP can be regenerated from ADP using acetyl phosphate and the enzyme acetate kinase, upon release of acetate. The reaction is irreversible and acetyl phosphate is a relatively cheap phosphate donor. Thus, in an enzyme membrane reactor, PEGderivatized ATP was consumed by a phosphorylase or a synthetase in a reaction leading to a product of interest, and the ATP was regenerated by the acetate kinase (Figure 10.9). 

In the ruminant mammary tissue, it appears that acetate and /3-hydroxybutyrate contribute almost equally as primers for fatty acid synthesis (Palmquist et al. 1969 Smith and McCarthy 1969 Luick and Kameoka 1966). In nonruminant mammary tissue there is a preference for butyryl-CoA over acetyl-CoA as a primer. This preference increases with the length of the fatty acid being synthesized (Lin and Kumar 1972 Smith and Abraham 1971). The primary source of carbons for elongation is malonyl-CoA synthesized from acetate. The acetate is derived from blood acetate or from catabolism of glucose and is activated to acetyl-CoA by the action of acetyl-CoA synthetase and then converted to malonyl-CoA via the action of acetyl-CoA carboxylase (Moore and Christie, 1978). Acetyl-CoA carboxylase requires biotin to function. While this pathway is the primary source of carbons for synthesis of fatty acids, there also appears to be a nonbiotin pathway for synthesis of fatty acids C4, C6, and C8 in ruminant mammary-tissue (Kumar et al. 1965 McCarthy and Smith 1972). This nonmalonyl pathway for short chain fatty acid synthesis may be a reversal of the /3-oxidation pathway (Lin and Kumar 1972). 

The preparation of trisaccharide 63 illustrates the activation and enzymic coupling of the 9-acetate of vV-acetylneuraminic acid, This involves the utilization of enzymes in a cascade of reactions which probably do not occur in cells (a) synthesis of Neu5,9Ac2 from the 6-acetate of vV-acetylmannosa-mine with the catabolic sialyl aldolase, (b) activation with CMPNeu5Ac synthetase, and (c) coupling. Acetylation in cells seems posterior to coupling. Terminal nonreducing vV-acetyl-9-O-acetylneuraminic acid residues appear... 

Acetic acid measurement involves conversion of acetate to acetyl-CoA by acetyl-CoA synthetase with the consumption of ATP (Boehringer Mannheim, 1986). Acetyl-CoA reacts with oxaloacetate and water in the presence of citrate synthetase to form citrate and CoA. Oxaloacetate for this reaction is obtained from malate by the action of malate dehydrogenase with concomitant conversion of NADH from NAD+. NADH is spectrophotometrically measured and correlated to acetic acid concentration. 

With the stereochemistry of the citrate lyase reaction determined, that of the Si citrate synthetase (the common enzyme) was established as shown in Fig. 70. Condensation of (J )-acetic-d, t acid (configuration known by synthesis) with oxalo-acetate gives what turns out to be mainly (2S,3/ )-citric-2-d,2-/ acid (112).41 When this acid is then cleaved with citrate lyase, the major product is (/ )-acetic-d, t acid, as established by the malate synthetase/fumarase diagnosis. It follows that both the Si-citrate synthetase and citrate lyase reactions must involve the same stereochemical course. Since that of the lyase reaction is inversion (vide supra), that of the Si synthetase reaction must be inversion also. And since the overall stereochemical result shown in Fig. 70 is not dependent on the magnitude of the... 

Some of the reactions of PO3- parallel enzymatic reactions promoted by adenosine triphosphate (ATP). Pyruvate kinase catalyzes the equilibration of ATP and pyruvate with adenosine diphosphate (ADP) and phosphoenol pyruvate (11,12). In a formal sense, this reaction resembles the preparations of enol phosphate (eqs. 6 and 7). Cytidine triphosphate synthetase catalyzes the reaction of uridine triphosphate with ammonia to yield cytidine triphosphate (13). In a formal sense, this reaction resembles the replacement of the ester carbonyl group of ethyl acetate by the nitrogen of aniline (eq. 8). 

The rate limiting step in fatty acid synthesis is catalyzed by acetyl-CoA carboxylase to produce malonyl-CoA at the expense of one ATP.31 Malonate and acetate are transferred from CoA to acyl carrier protein in the cytosolic fatty acid synthetase complex, where chain extension leads to the production of palmitate. Palmitate can then be transferred back to CoA, and the chain can be extended two carbons at a time through the action of a fatty acid elongase system located in the endoplasmic reticulum. The >-hydroxylation that produces the >-hydroxyacids of the acylceramides is thought to be mediated by a cytochrome p450 just when the fatty acid is long enough to span the endoplasmic reticular membrane. 

Animal and bacterial enzymes that utilize or synthesize carbamyl phosphate have activity with acetyl phosphate. Acyl phosphatase hydrolyzes both substrates, and maybe involved in the specific dynamic action of proteins. Ornithine and aspartic transcarbamylases also synthesize acetylornithine and acetyl aspartate. Finally, bacterial carbamate kinase and animal carbamyl phosphate synthetase utilize acetyl phosphate as well as carbamyl phosphate in the synthesis of adenosine triphosphate. The synthesis of acetyl phosphate and of formyl phosphate by carbamyl phosphate synthetases is described. The mechanism of carbon dioxide activation by animal carbamyl phosphate synthetase is reviewed on the basis of the findings concerning acetate and formate activation. 

The activation of acetate, formate, and bicarbonate may be carried out by the synthetase by an analogous mechanism, conducing to the synthesis of acetyl-P, formyl-P, and an unidentified compound (perhaps carboxyl-P), respectively. The activation possibly occurs in one step, utilizing 1 mole of ATP per mole of product synthesized (Reaction 12) ... 

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