0-Acetyl serine

Smith, I. K. Evidence for o-acetyl-serine in Nicotiana tabacum. Phytochemistry 1977 16 1293-1294. Ishiguro, S., and S. Sugawara. Comparison of volatile N-containing compounds in the smoke of Lamina and Midrib of flue-cured tobacco leaves. Agr Biol Chem 1977 41 377. Chuman, T., M. Noguchi, A. Okhubo, and S. Toda. The structure of a novel... 

Acetylcholine is a neurotransmitter that relays nerve impulses across the neuromuscular Junction. Acetylcholinesterase (AcChE) rapidly breaks dovm acetylcholine, thereby loweringits concentration in the synaptic cleft and ensuring that nerve impulses are of a finite length. As shown in Fig. 17.38, a nucleophilic serine residue reacts with the substrate to form an acetyl-serine intermediate (100) with concomitant release of choline. This intermediate is then rapidly hydrolyzed by wa-... 

As an alternative to this complicated approach, some success has been achieved with direct chemical deactylation in the case of proteins with N-acetyl serine and threonine residues (serine is actually the most commonly N-acetylated residue ) by treatment with trifluoroacetic acid for an extended period. This approach capitalizes on acid-catalyzed N —> O acyl shifting. 

O-acetyl homoserine-O-acetyl serine sulfhydrylase, required for sulfur amino acid synthesis... 

Our laboratory has studied the stereochemistry of methyl group formation in a number of a, 0 elimination reactions of amino acids catalyzed by pyridoxal phosphate enzymes. The reactions include the conversions of L-serine to pyruvate with tryptophan synthase 02 protein (78) and tryptophanase (79), of L-serine and l-tyrosine with tyrosine phenol-lyase (80), and l-cystine with S-alkylcysteine lyase (81). In the latter study, the stereospecific isotopically labeled L-cystines were obtained enzymatically by incubation of L-serines appropriately labeled in the 3-position with the enzyme O-acetyl serine sulfhy-drase (82). The serines tritiated in the 3-position were prepared enzymatically starting from [l-3H]glucose and [l-3H]mannose by a sequence of reactions of known stereochemistry (81). The cysteines were then incubated with 5-alkyl-cysteine lyase in 2H20 as outlined in Scheme 19. The pyruvate was trapped as lactate, which was oxidized with K2Cr202 to acetate for analysis. Similarly, Cheung and Walsh (71) examined the conversion of D-serine to pyruvate with... 

Jornvall and Harris (91) presented data for the structures around all of the 14 cysteine residues in each protein chain. Analysis by Jornvall (92,93) of different peptide mixtures obtained after treatment of the protein with trypsin (before or after maleylation), chymotrypsin, pepsin, cyanogen bromide, or thermolysin yielded amino acid sequence information for all parts of the subunit and the primary structure of the whole protein chain was deduced (5S). It was found to contain 374 residues and is shown in Table I. An acetylated serine residue is at the N-terminus and the reactive cysteine residue is at position 46. Some residues are unevenly distributed (PS). Six of the seven histidine residues are in the N-terminal half of the molecule, the two tryptophan residues are in either terminal region, the four tyrosine residues are in the middle of the primary structure, and none of the 14 cysteine residues occur in the C-terminal quarter of the molecule. A characteristic distribution of hydrophobic residues was also noticed (93), which may now be partly correlated with the presence of large hydrophobic cores in the tertiary structure of the protein (Section II,C,3). Most regions of the primary structure were analyzed in many different overlapping peptides (92-9 ) with a corresponding increase in reliability. The structure is in excellent agreement with the total composition determined by acid hydrolysis (93). It is compatible with independently determined partial structures of... 

Trout testis histone H2A is phosphorylated on the N-terminal acetyl-serine residue (103) ... 

Amino-acid analogs and uncommon L-amino acids W-acetyl-aspartate, W-acetyl-serine, oi-amino-n-butyrate, 3-aminoisobutyrate, aspartate ethyl or methyl ester, citrulline, cysteate, fumarate, glutathione, homoserine, erythro- and threo-p-hydroxyaspartate, isoasparagine, isoserine, malate, a- and p-methylaspartate, methylserine, phenol, serine amide, serine methyl ester, succinate [498, 747]... 

Biosynthesis metabolism In plants from O-acetyl-serine in animal tissue, on the other hand, by cleavage of cystathionine formed fium 5-adenosylmethi-onine. Since methionine is an essential amino acid, Cys may also be considered as essential. C. can be converted by several routes to pyruvic acid and is metabolized in the citric acid cycle. Cys is a component of glutathione. 

A possible minor route of serine degradation could be via the conversion of serine to O-acetyl serine by serine transacetylase which has been partially purified from kidney bean seedlings by Smith and Thompson (1971). O-acetyl... 

ASS is known to deactivate COX by irreversibly acetylating serine 530 in the active site of COX-1 [116], and correspondingly serine 516 in COX-2 [117]. Hence, Ott et al. were interested in the potential of Co-ASS 31 to acetylate COX [117]. The exact acetylation sites of COX-2 after incubation with Co-ASS were examined by LC-ESI tandem mass spectrometry. In contrast to ASS, incubation with Co-ASS did not lead to acetylation of serine 516, but to acetylation of several lysine residues, namely lysine 166, lysine 346, lysine 432, and lysine 598 (Figure 1.16). Lysine 346 is part of the entrance channel of the active site and thus acetylation could hinder the access of the substrate. Lysine 166 and lysine 432 are close to the heme prosthetic group, and therefore acetylation of these residues could abolish the function of the protein. In analogy to ASS, these modifications can be assimied to be irreversible. 

Cysteine formation through the addition of thiosulphate to serine or O-acetyl serine may play a role in the sulphur metabolism of some organisms. The reactions involved are similar in form to those described above, with S-sulphocysteine serving an intermediary role. Since thiosulphate is not generally considered to be on the main line of inorganic sulphur metabolism this probably represents an adaptation to certain special environments. 

EF-T 43 N-terminal acetyl-serine heat labile binds... 

The phenolic hydroxyl group of tyrosine, the imidazole moiety of histidine, and the amide groups of asparagine and glutamine are often not protected in peptide synthesis, since it is usually unnecessary. The protection of the hydroxyl group in serine and threonine (O-acetylation or O-benzylation) is not needed in the azide condensation procedure but may become important when other activation methods are used. 

The first domain of one subunit of the fatty acid synthase interacts with the second and third domains of the other subunit that is, the subunits are arranged in a head-to-tail fashion (Figure 25.9). The first step in the fatty acid synthase reaction is the formation of an acetyl-O-enzyme intermediate between the acetyl group of an acetyl-CoA and an active-site serine of the acetyl trails-... 

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