Transfer reaction, acetyl

We are familiar with several examples of chemical activation as a strategy for group transfer reactions. Acetyl-CoA is an activated form of acetate, biotin and tetrahydrofolate activate one-carbon groups for transfer, and ATP is an activated form of phosphate. Luis Leloir, a biochemist in Argentina, showed in the 1950s that glycogen synthesis depended upon sugar nucleotides, which may be... 

Many reactions like this occur in living organisms, and biochemists call them acyl transfer reactions. Acetyl-coenzyme A, discussed in Special Topic E in WileyPLUS, often serves as a biochemical acyl transfer agent. Acyl substitution reactions are of tremendous importance in industry as well, as described in the chapter opening essay and Special Topic C in WileyPLUS. 

The acetyl transfer reactions of acetylated pyrazolones (acylotropy) have been carefully studied by Arakawa and Miyasaka (74CPB207,74CPB214) (Section 4.04.2.1.3(x)). Methylation of 3-methyl-l-phenyl-4-phenylazo-5-pyrazolone (402) yields, depending on the experimental conditions, the N- and the O-methylated derivatives (483) and (484) (66BSF2990). These derivatives have been used as model compounds in a study of the tautomerism of (402) (structure 139 Section 4.04.1.5.2). 

The mechanism of the C02 transfer reaction with acetyl CoA to give mal-onyl CoA is thought to involve C02 as the reactive species. One proposal is that loss of C02 is favored by hydrogen-bond formation between the A -carboxy-biotin carbonyl group and a nearby acidic site in the enzyme. Simultaneous deprotonation of acetyl CoA by a basic site in the enzyme gives a thioester eno-late ion that can react with C02 as it is formed (Figure 29.6). 

Histone Acetylation. Figure 1 Histone acetylation is a posttranslational modification of lysine residues of histones. This modification is catalyzed by histone actyl transferases (HATs), which transfer an acetyl group (yellow) from acetyl-Coenzyme A onto the E-amino group of the lysine residue. Histone deacetylation is catalyzed by histone deacetylases (HDACs), which hydrolyze the lysine bound acetyl group. HDAC inhibitors like Trichostatin A (TSA) are known to inhibit the deacetylation reaction in vivo and in vitro. 

The subunits of CODH/ACS have been isolated (see earlier discussion). The isolated a subunit contains one Ni and four Fe and has spectroscopic properties (186) similar to those of Cluster A, the active site of acetyl-CoA synthesis (212). Unfortunately, it has no ACS activity. Therefore, ACS activity may reside in the a subunit or it may require both the a and the fi subunits. If Clusters B and/or C of the B subunit are involved in acetyl-CoA synthesis, one possible role could be in electron transfer. Although acetyl-CoA synthesis and the CO/ exchange reactions do not involve net electron transfer, both of these reactions are stimulated by ferredoxin, indicating that internal electron transfer within CODH/ACS may be required during the reaction (121). Further studies with the isolated subunits and the reconstitu-... 

The introduction of an electron-withdrawing group such as acetyl at the oxime oxygen will decrease the intramolecular electron transfer reaction from the nitrogen lone pair and will enhance the aza-di-jr-methane rearrangement134-138 (equation 78). 

Once the human body has a supply of pantothenic acid, it can add the remaining parts to create the intact molecule. The business part of coenzyme A is a terminal sulfhydryl (—SH) group. It is here that acyl (e.g., the acetyl group, —COCH3) groups are attached in the process of acyl transfer reactions. There are a large number of such reactions in human metabolism and they are concerned with all aspects of... 

This enzyme [EC 2.3.1.5], also known as acetyl-CoA arylamine A-acetyltransferase and arylamine acetylase, catalyzes the reaction of acetyl-CoA with an arylamine to produce coenzyme A and an A-acetylarylamine. This enzyme exhibits a low specificity with respect to the aromatic amine substrate. In fact, even serotonin can serve as a substrate. The enzyme has also been reported to catalyze acetyl-transfer reactions between arylamines without the use of coenzyme A. 

Cationic polymerization of formaldehyde (which should be carried out under the driest possible conditions to avoid transfer reactions) can be initiated with protic acids, Lewis acids (see Sect. 3.2.1.1), or other compounds that yield cations such as acetyl perchlorate or iodine ... 

FIGURE 21-1 The acetyl-CoA carboxylase reaction. Acetyl-CoA carboxylase has three functional regions biotin carrier protein (gray) biotin carboxylase, which activates C02 by attaching it to a nitrogen in the biotin ring in an ATP-dependent reaction (see Fig. 16-16) and transcarboxylase, which transfers activated C02 (shaded green) from... 

Harting, J., Velick, S. F., Transfer Reactions of Acetyl Phosphate Cata-... 

The protective group can be removed by reaction of a catalytic amount of Pdp QHs) and excess dimethyl malonate. This transfer reaction does not affect usual protective groups. On the other hand, the acetyl groups can be removed selectively by hy-drazinolysis. 

The acetyl-CoA transfers its acetyl group to oxaloace-tate, thereby generating citrate. In a cyclic series of reactions, the citrate is subjected to two successive decarboxylations and four oxidative events, leaving a four-carbon compound malate from which the starting oxaloacetate is regenerated. 

After malonyl-CoA synthesis, the remaining steps in fatty acid synthesis occur on fatty acid synthase, which exists as a multienzyme complex. In the initial reactions acetyl-CoA and malonyl-CoA are transferred onto the protein complex by acetyl-CoA transacylase and malonyl-CoA transacylase (step 1 and step 2 in fig. 18.12a). The acceptor for the acetyl and malonyl groups is acyl carrier protein (ACP). ACP also carries all of the intermediates during fatty acid biosynthesis. The prosthetic group that binds these intermediates is... 

Fatty acid synthesis begins when the substrates, acetyl-CoA and malonyl-CoA, are transferred onto the protein by malonyl-CoA acetyl-CoA-ACP transacylase (MAT, steps 1 and 2 in fig. 18.12a). The numbers in parentheses below the abbreviation of the enzyme in this figure refer to the reactions shown in fig. 18.12. (Whereas E. coli has separate enzymes that catalyze the transfer of acetyl- and malonyl-CoA to ACP, both reactions are catalyzed by the same enzymatic activity (MAT) on the animal fatty acid synthase.) Subsequently, /3-ketobutyryl-ACP and CO2 are formed in a condensation reaction catalyzed by /3-ketoacyl-ACP synthase (KS, step 3 in fig. 18.12a). 

The biosynthesis of L-cysteine entails the sulfhydryl transfer to an activated form of serine. This pathway to L-cysteine has been most thoroughly studied in E. coli. In the first step an acetyl group is transferred from acetyl-CoA to serine to yield (9-acetylserine (fig. 21.8a). The reaction is catalyzed by serine transacetylase. The formation of cysteine itself is catalyzed by O-acetylserine sulfhydrylase. 

Sialyl residues in oligosaccharides are introduced by the reaction of cyti-dine monophosphate-V-acetylneuraminic acid (49) as the sugar donor with the appropriate substrate, in the presence of specific transferases. Three of these have been utilized in syntheses which may be considered to be preparative. None are readily available. The most common, which we have called STA (see Table I), catalyzes the transfer of a 5-acetamido-3,5-di-deoxy-D-g/ycm>-a -D-ga/arfo-2-hexulopyranosonic acid unit (the a-D-pyra-nose form of JV-acetylneuraminic acid) to the primary position of D-galactose in a JV-acetyllactosamine residue.86 This enzyme also transfers vV-acetyl-9-O-acetylneuraminic acid (20) and V-glycolylneuraminic acid (12) from the corresponding cytidine monophosphate derivatives.16 The commercial enzyme is rather expensive, but pork liver from a butcher is a... 

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