Amino acids acetylated

Conjugation involves addition of an endogenous moiety to a foreign molecule, which may be a product of a phase 1 reaction. Major phase 2 routes conjugation with glucuronic acid, sulfate, glutathione amino acids acetylation methylation. Enzymes involved are transferases except in the case of amino acid conjugation where the first step is catalyzed by an acyl CoA synthetase, then a transferase is involved. 

Amino acid degradation amino acids-----> acetyl-CoA, citric acid cycle intermediates... 

N-terminal amino acid Acetyl-Ala Acetyl-Ser Acetyl-Ser... 

Aromatic amino acids Acetylated Acyclovir Guanethidine Penicillins... 

Many compounds can form acetyl-CoA, such as fats, carbohydrates, and many amino acids. Acetyl-CoA can also form fats and ketone bodies, as well as feed directly into the citric acid cycle. 

Protein Turnover in Liver 586 Some Aspects of Amino Acid Metabolism 587 Hippuric Acid Synthesis Cholate Synthesis Amino Acid Acetylation T ransmethylation... 

Acetylation may occur with -NHg, -OH, and -SH groups. Acetylation of primary aromatic amines and sulfonamide nitrogens are the most important of these reactions in the inactivation of drugs. These reactions occur in most laboratory and domestic animals. The dog is unable to acetylate aromatic amines or hydrazines, probably due to a lack of selective acetylating enzymes. Deacetylation of the conjugate may occur in certain species, e.g. the chicken de-acetylates aromatic amines, and dogs deacetylate aliphatic amino acids. Acetylation reactions have also been reported to occur in amphibia, fish, and a few insect species [20]. 

Study of the metabolism, fundamental and vital to living things, has led to a detailed understanding of the processes involved. A complex web of enzyme-catalysed reactions is now apparent, which begins with carbon dioxide and photosynthesis and leads to, and beyond, diverse compounds called primary metabolites, e.g. amino acids, acetyl-coenzyme A, mevalonic acid, sugars, and nucleotides [2, 3]. Critical to the overall energetics involved in metabolism is the coenzyme, adenosine triphosphate (ATP), which serves as a common energy relay and co-operates, like other coenzymes, with particular enzymes in the reactions they catalyse. 

It is interesting to note that secondary metabolites are biosynthesised essentially from a handful of primary metabolites a-amino acids, acetyl-coenzyme A, mevalonic acid, and intermediates of the shikimic acid pathway. It is these starting points for the elaboration of secondary metabolites which allow their classification, and also their discussion as discrete groups (Chapters 3 to 7). In the remainder of this chapter various aspects of biosynthesis of general importance to the discussion in Chapter 3 and succeeding chapters is reviewed. The first examples of primary and secondary metabolite biosynthesis will be found in Sections 1.1.2 and 1.1.3. Chapter 2 is devoted to a brief discourse on the various techniques used in studying the biosynthesis of secondary metabolites. 

Some amino-acids, e.g, glycine, can also be acetylated by this method. 

The most suitable synthetic method for these products is the heterocyc-lization reaction of N-thioacyl derivatives of amino acids (202) with phosphorus tribromide (378, 442-450, 559, 560) or anhydrous trifluoroacetic acid (448, 449, 451, 452) (Scheme 103). Treatment of N-thioacyl amino acids with acetic anhydride leads directly to the thiazolylacetate without isolation of an intermediate thiazolinone (365. 452). 2-Alkoxy-derivatives of A-2-thiazoline-5-one, however, can be obtained without acetylation by this method (453, 454). 

Nonvolatile analytes must be chemically converted to a volatile derivative before analysis. For example, amino acids are not sufficiently volatile to analyze directly by gas chromatography. Reacting an amino acid with 1-butanol and acetyl chloride produces an esterfied amino acid. Subsequent treatment with trifluoroacetic acid gives the amino acid s volatile N-trifluoroacetyl- -butyl ester derivative. 

While electrospray is used for molecules of all molecular masses, it has had an especially marked impact on the measurement of accurate molecular mass for proteins. Traditionally, direct measurement of molecular mass on proteins has been difficult, with the obtained values accurate to only tens or even hundreds of Daltons. The advent of electrospray means that molecular masses of 20,000 Da and more can be measured with unprecedented accuracy (Figure 40.6). This level of accuracy means that it is also possible to identify post-translational modifications of proteins (e.g., glycosylation, acetylation, methylation, hydroxylation, etc.) and to detect mass changes associated with substitution or deletion of a single amino acid. 

Inactivation and Removal of Viruses. In developing methods of plasma fractionation, the possibiHty of transmitting infection from human vimses present in the starting plasma pool has been recognized (4,5). Consequentiy, studies of product stabiHty encompass investigation of heat treatment of products in both solution (100) and dried (101) states to estabHsh vimcidal procedures that could be appHed to the final product. Salts of fatty acid anions, such as sodium caprylate [1984-06-17, and the acetyl derivative of the amino acid tryptophan, sodium acetyl-tryptophanate [87-32-17, are capable of stabilizing albumin solutions to 60°C for 10 hours (100) this procedure prevents the transmission of viral hepatitis (102,103). The degree of protein stabilization obtained (104) and the safety of the product in clinical practice have been confirmed (105,106). The procedure has also been shown to inactivate the human immunodeficiency vims (HIV) (107). 

With active methylene compounds, the carbanion substitutes for the hydroxyl group of aHyl alcohol (17,20). Reaction of aHyl alcohol with acetylacetone at 85°C for 3 h yields 70% monoaHyl compound and 26% diaHyl compound. Malonic acid ester in which the hydrogen atom of its active methylene is substituted by A/-acetyl, undergoes the same substitution reaction with aHyl alcohol and subsequendy yields a-amino acid by decarboxylation (21). 

In these cases, it is better to protect the carboxyl group. Optimized conditions for A/-acetylation have been studied (78). A/-Acylation can be utilized for protecting the amino group in the reaction of amino acids, for example in peptide synthesis. 

Table 3. Comparison of Electrophilic Fluorination of Aromatic Amino Acids with [ F]fluorine or [ F]acetyl Hypofluorite" [25]...

Pyruvate kinase possesses allosteric sites for numerous effectors. It is activated by AMP and fructose-1,6-bisphosphate and inhibited by ATP, acetyl-CoA, and alanine. (Note that alanine is the a-amino acid counterpart of the a-keto acid, pyruvate.) Furthermore, liver pyruvate kinase is regulated by covalent modification. Flormones such as glucagon activate a cAMP-dependent protein kinase, which transfers a phosphoryl group from ATP to the enzyme. The phos-phorylated form of pyruvate kinase is more strongly inhibited by ATP and alanine and has a higher for PEP, so that, in the presence of physiological levels of PEP, the enzyme is inactive. Then PEP is used as a substrate for glucose synthesis in the pathway (to be described in Chapter 23), instead... 

---