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Transamination biological

The biologically active form of vitamin Bg is pyridoxal-5-phosphate (PEP), a coenzyme that exists under physiological conditions in two tautomeric forms (Figure 18.25). PLP participates in the catalysis of a wide variety of reactions involving amino acids, including transaminations, a- and /3-decarboxylations, /3- and ") eliminations, racemizations, and aldol reactions (Figure 18.26). Note that these reactions include cleavage of any of the bonds to the amino acid alpha carbon, as well as several bonds in the side chain. The remarkably versatile chemistry of PLP is due to its ability to... [Pg.594]

The biological importance of transamination was confirmed using 15N-labeling experiments (Tannenbaum and Shemin, 1950). 15N-leucine incubated with pig heart muscle gave highly labelled 15N-glutamate, evidence that leucine could be transaminated. Isotope experiments were then extended to the whole range of amino acids. [Pg.111]

The terminology vitamin Bg covers a number of structurally related compounds, including pyridoxal and pyridoxamine and their 5 -phosphates. Pyridoxal 5 -phosphate (PLP), in particular, acts as a coenzyme for a large number of important enzymic reactions, especially those involved in amino acid metabolism. We shall meet some of these in more detail later, e.g. transamination (see Section 15.6) and amino acid decarboxylation (see Section 15.7), but it is worth noting at this point that the biological role of PLP is absolutely dependent upon imine formation and hydrolysis. Vitamin Bg deficiency may lead to anaemia, weakness, eye, mouth, and nose lesions, and neurological changes. [Pg.246]

The amino acid and nucleotide biosynthetic pathways make repeated use of the biological cofactors pyridoxal phosphate, tetrahydrofolate, and A-adenosylmethionine. Pyridoxal phosphate is required for transamination reactions involving glutamate and for other amino acid transformations. One-carbon transfers require S-adenosyhnethionine and tetrahydrofolate. Glutamine amidotransferases catalyze reactions that incorporate nitrogen derived from glutamine. [Pg.841]

NMR studies have been carried out on Schiff bases derived from pyridoxal phosphate and amino acids, since they have been proposed as intermediates in many important biological reactions such as transamination, decarboxylation, etc.90 The pK.d values of a series of Schiff bases derived from pyridoxal phosphate and a-amino adds, most of which are fluorinated (Figure 11), have been derived from H and19F titration curves.91 The imine N atom was found to be more basic and more sensitive to the electron-withdrawing effect of fluorine than the pyridine N atom. Pyridoxal and its phosphate derivative are shown in Figure 12a. The Schiff base formation by condensation of both with octopamine (Figure 12b) in water or methanol solution was studied by 13C NMR. The enolimine form is favoured in methanol, while the ketoamine form predominates in water.92... [Pg.726]

Torchinsky, Y. M., Transamination, its discovery, biological and chemical aspects (1937-1987). Trends Biochem. Sci. 12 115-117, 1987. [Pg.531]

Another interesting example of metal-directed chemistry involving the stabilisation and reactivity of imines is seen in the reaction of pyridoxal with amino acids. This reaction is at the basis of the biological transamination of amino acids to a-ketoacids, although the involvement of metal ions in the biological systems is not established. The reaction of pyridoxal (5.27) with an amino acid generates an imine (5.28), which is stabilised by co-ordination to a metal ion (Fig. 5-55). [Pg.116]

In addition to resolution approaches, there are three main methods to prepare amino acids by biological methods addition of ammonia to an unsaturated carboxylic acid the conversion of an a-keto acid to an amino acid by transamination from another amino acid, and the reductive animation of an a-keto acid. These approaches are discussed in Chapter 19 and will not be discussed here to avoid duplication. The use of a lyase to prepare L-aspartic acid is included in this chapter as is the use of decarboxylases to access D-glutamic acid. [Pg.24]

The interest in the mechanisms of SchifF base hydrolysis stems largely from the fact that the formation and decomposition of SchifF base linkages play an important role in a variety of enzymatic reactions, for example, carbonyl transfers involving pyridoxal phosphate, aldol condensations, /3-decarboxylations and transaminations. The mechanisms for the formation and hydrolysis of biologically important SchifF bases, and imine intermediates, have been discussed by Bruice and Benkovic (1966) and by Jencks (1969). As the consequence of a number of studies (Jencks, 1959 Cordes and Jencks, 1962, 1963 Reeves, 1962 Koehler et al., 1964), the mechanisms for the hydrolysis of comparatively simple SchifF bases are reasonably well understood. From the results of a comprehensive kinetic investigation, the mechanisms for the hydrolysis of m- and p-substituted benzylidine-l,l-dimethylethylamines in the entire pH range (see, for example, the open circles in Fig. 13) have been discussed in terms of equations (23-26) (Cordes and Jencks, 1963) ... [Pg.337]

Ivanov VI and Karpeisky MY (1969) Dynamic three-dimensionai modei for enzymic transamination. Advances in Enzymology and Related Areas of Molecular Biology 32, 21-53. [Pg.269]

Examples include acetal hydrolysis, base-catalyzed aldol condensation, olefin hydroformylation catalyzed by phosphine-substituted cobalt hydrocarbonyls, phosphate transfer in biological systems, enzymatic transamination, adiponitrile synthesis via hydrocyanation, olefin hydrogenation with Wilkinson s catalyst, and osmium tetroxide-catalyzed asymmetric dihydroxylation of olefins. [Pg.256]

The urea cycle is the most important process in biological ammonia detoxication, (s. pp 57, 266) (s. figs. 3.12, 3.13) It is directly linked with amino-acid metabolism and thus also with NH2 donors and precursors through specific amino acids and transamination processes. Here, the major transamination processes are those involving glutamate and oxalacetate as well as a-ketoglutarate and aspartate. [Pg.861]

Fig. 5. The amino terminus of class I/II secretory phospholipases A. Schematic stereoview of the web of hydrogen bonds that stabilizes the amino terminus of class I/II enzymes (class II Crotalus atrox) (Brunie et al., 1985 Scott et al., 1992, copyrighted by the Journal of Biological Chemistry). Modification of the amino terminus (e.g., transamination) structurally disorders the adjacent helix and peptide. A Gin is almost invariant at sequence position 4. Replacement of Gln-4 with an Asn, as in the human nonpancreatic enzyme, permits small (<1 A) movements of the amino-terminal helix, which can narrow the hydrophobic channel (Scott e/a/., 1991). Fig. 5. The amino terminus of class I/II secretory phospholipases A. Schematic stereoview of the web of hydrogen bonds that stabilizes the amino terminus of class I/II enzymes (class II Crotalus atrox) (Brunie et al., 1985 Scott et al., 1992, copyrighted by the Journal of Biological Chemistry). Modification of the amino terminus (e.g., transamination) structurally disorders the adjacent helix and peptide. A Gin is almost invariant at sequence position 4. Replacement of Gln-4 with an Asn, as in the human nonpancreatic enzyme, permits small (<1 A) movements of the amino-terminal helix, which can narrow the hydrophobic channel (Scott e/a/., 1991).
The molecule is a chiral analogue of pyridoxamine and transamination occurs chemically by a mechanism similar to the biological one described in the chapter (pp. 1384-6). The zinc holds the molecule in a fixed conformation during reaction. The key step is the protonation of the enamine as that produces the new chiral centre. If the chain is across the top of the ring, protonation occurs preferentially from underneath. Hydrolysis gives the new amino acid (Phe) and the pyridoxal analogue, which can be recycled by reductive amination via the oxime. [Pg.483]

The kinetic acidity of the methylene protons on coordinated amino acid fragments is enhanced in imine complexes such as those derived from the ligands (116) and (117). This enhanced acidity is responsible for both racemization and transamination i processes, which have been studied in detail because of the biologically important pyridoxal-activated enzyme... [Pg.207]


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See also in sourсe #XX -- [ Pg.76 ]




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