Kinetic of amino acids

Dobbins DC, Pfaender FK. 1987. Kinetics of amino acids and m- cresolbiogradation in an unpolluted aquifer soil profile. American Society ofMicrobiol Abstr 87th Annual Meeting, Atlanta, GA, 298. 

M Friedman, R Liardon. Racemization kinetics of amino acid residues in alkali-treated soybean proteins. J Agric Food Chem 33 666-672, 1985. 

Smith QR, Takasato Y. Kinetics of amino acid transport at the blood-brain barrier studied using an in situ brain perfusion technique. Ann N Y Acad Sci 1986 481 186-201. 

MaM, Chen B, Luo X, Tan II, He D, Xie Q, Yao S, Study on the transport selectivity and kinetics of amino acids through di(2-ethylhe.xyl) phosphoric acid-kerosene bulk liquid membrane. J Membr Sci 2004 234 101-109. 

Ten Have GA, et al. Absorption kinetics of amino acids, peptides, and intact proteins. Int J Sport Nutr Exerc Metab. 2007 17(Suppl) S23-36. 

Remes et al. (1976) also investigated the kinetics of the N-azo coupling of nine a-amino acids. They are aware of earlier investigations in which the major products were pentaz-1,4-dienes, but they claim that under their reaction conditions (pH 8.00-10.25, thirty-fold excess of amino acid) only the triazenes are formed. The rates were found to be first-order with respect to diazonium ion which is consistent with their conclusion however, in the opinion of the present author the results suggest a significant (say, 10%) contribution of pentazdiene formation to the total rate process. No significant correlation was found between the rate constants and the acidity constants of the nine amino acids. 

The mechanism of decarboxylation of acids containing an amino substituent is further complicated by the possibility of protonation of the substituent and the fact that the species NH2ArCOOH is kinetically equivalent to the zwitterion NHj ArCOO. Both of these species, as well as the anion NH2 ArCOO" and even NH3 ArCOOH must be considered. Willi and Stocker644 investigated by the spectroscopic method the kinetics of the acid-catalysed decarboxylation of 4-aminosalicyclic acid in dilute hydrochloric acid, (ionic strength 0.1, addition of potassium chloride) and also in acetate buffers at 20 °C. The ionisation constants K0 = [HA][H+][H2A+] 1 (for protonation of nitrogen) and Kx = [A"][H+] [HA]-1, were determined at /i = 0.1 and 20 °C. The kinetics followed equation (262)... 

In nature, aminotransferases participate in a number of metabolic pathways [4[. They catalyze the transfer of an amino group originating from an amino acid donor to a 2-ketoacid acceptor by a simple mechanism. First, an amino group from the donor is transferred to the cofactor pyridoxal phosphate with formation of a 2-keto add and an enzyme-bound pyridoxamine phosphate intermediate. Second, this intermediate transfers the amino group to the 2-keto add acceptor. The readion is reversible, shows ping-pong kinetics, and has been used industrially in the production ofamino acids [69]. It can be driven in one direction by the appropriate choice of conditions (e.g. substrate concentration). Some of the aminotransferases accept simple amines instead of amino acids as amine donors, and highly enantioselective cases have been reported [70]. 

The main application of the enzymatic hydrolysis of the amide bond is the en-antioselective synthesis of amino acids [4,97]. Acylases (EC 3.5.1.n) catalyze the hydrolysis of the N-acyl groups of a broad range of amino acid derivatives. They accept several acyl groups (acetyl, chloroacetyl, formyl, and carbamoyl) but they require a free a-carboxyl group. In general, acylases are selective for i-amino acids, but d-selective acylase have been reported. The kinetic resolution of amino acids by acylase-catalyzed hydrolysis is a well-established process [4]. The in situ racemization of the substrate in the presence of a racemase converts the process into a DKR. Alternatively, the remaining enantiomer of the N-acyl amino acid can be isolated and racemized via the formation of an oxazolone, as shown in Figure 6.34. 

Figure 6.38 Dynamic kinetic resolution of amino acid amides.

In this chapter, we shall focus on the molecular aspects of amino acid transport and its regulation in Saccharomyces cerevisiae. Kinetic, biochemical and genetic aspects of the amino acid transport systems of eukaryotic microorganisms have been reviewed earlier [7,8]. 

A large number of amino acid transporters have been detected by isolating mutations which selectively inactivate one permease without altering enzyme activities involving the corresponding amino acid. Competitive inhibition, kinetics and regulatory behaviour have also been used as criteria to distinguish one transport system from another (see section 4.2). 

Manley, W. R, G. H. Miller, and J. Czywczynski (2000), Kinetics of aspartic acid racem-ization, in Goodfriend, G. A., M. J. Collins, M. L. Fogel, S. A. Macko, and J. F. Wehmiller (eds.), Perspectives in Amino Acid and Protein Geochemistry, Oxford Univ. Press, New York, pp. 202-218. 

Asano, Y. and Yamaguchi, S. (2005) Dynamic kinetic resolution of amino acid amide catalyzed by D-aminopeptidase and a-amino-e-caprolactam racemase. Journal of the American Chemical Society, 127 (21), 7696-7697. 

Bada, J.L. and Shou, M-Y. (1980). Kinetics and mechanism of amino acid racemisation in aqueous solution and in bones. In Biogeochemistry of Amino Acids, ed. Hare P.E., Hoering T.C. and King K. Jr, John Wiley, New York, pp. 235-255. 

Coenzymes facilitate chemical reactions through a range of different reaction mechanisms, some of which will be discussed in detail in this review. However, in all cases structural features of the coenzyme allow particular reactions to proceed along a mechanistic pathway in which reaction intermediates are more thermodynamically and kinetically accessible. When incorporated into apoen-zyme active sites, the coenzyme reactivity is influenced by a well-defined array of amino acid functional groups. For a given coenzyme, the particular array of amino acids presented by the different apoenzymes can drastically alter the degree of rate acceleration and product turnover and can specify the nature of the reaction catalyzed. 

The biosynthetic incorporation of amino acids into proteins makes these metabolites valuable endogenous tracers for the characterization of protein turnover. Of the naturally occurring amino acids, administration of a bolus dose of pH]leucine is widely used as a tracer in kinetic investigations of protein synthesis and secretion. 

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