Naming, acid anhydrides enzymes

The second example in this chapter is the carboxypeptidase A (CPA) [42, 43]. CPA is an exo-peptidase which can hydrolyze the C terminal amino acid from the peptide or ester substrates, whose X-ray structures have been reported for its native form [44, 45] or enzyme-inhibitor complex [46-51]. In addition, an X-ray stmc-mre of enzyme complexed with the proteolysis product was also reported [52]. No matter accumulation of experimental data, its reaction mechanisms still remain incompletely understood [53]. In particular, two major mechanisms, promoted-water pathway and nucleophilic pathway (traditionally it was named as anhydride pathway), using a peptide as the model substrate are depicted in Fig. 9.4. The nucleophilic pathway envisages an acyl-enzyme (AE) intermediate resulting from direct... 

Natural supports (agarose, dextran, cellulose, porous glass, silica, the optical fiber itself or alumina) and synthetic resins (acrylamide-based polymers, methacrylic acid-based polymers, maleic anhydride-based polymers, styrene-based polymers or nylon, to name a few) have been applied for covalent attachment of enzymes. These materials must display a high biocatalyst binding capacity (as the linearity and the limit of detection of the sensing layers will be influenced by this value), good mechanical and chemical stability, low cost, and ease of preparation. 

Trypsin was named more than 100 years ago. It and chymotrypsin were among the first enzymes to be crystallized, have their amino acid sequences determined, and have their three-dimensional structure outlined by x-ray diffraction. Furthermore, both enzymes hydrolyze not only proteins and peptides but a variety of synthetic esters, amides, and anhydrides whose hydrolysis rates can be measured conveniently, precisely and, in some instances, extremely rapidly. As a result, few enzymes have received more attention from those concerned with enzyme kinetics and reaction mechanisms. The techniques developed by the pioneers in these various fields have enabled other serine proteases to be characterized rapidly, and the literature on this group of enzymes has become immense. It might be concluded that knowledge of serine proteases is approaching completeness and that little remains but to fill in minor details. 

The hydrolysis of these compounds by the enzyme was determined by the isolation of the individual substances. The isolation of the amino acids soluble with difficulty in water, namely, tyrosine and cystine, presented no great difficulty, since those compounds crystallised out during the process of hydrolysis, but in the other cases the amino acids required separation from unchanged dipeptide. The ester method here again proved its usefulness the esters of the simple monoamino acids are easily volatile in vacuo and can be characterised by the methods previously described those of the dipeptides are not volatile and are characterised by conversion into their diketopiperazines or anhydrides by the action of ammonia, which compounds are less soluble than the dipeptides themselves and are thus capable of separation by filtration. 

Scheme 9.6. A cartoon representation of the enzyme (named glyceraldehyde-3-phosphate dehydrogenase, EC 1.2.1.12) catalyzed oxidation of the aldehyde glyceraldehyde-3-phosphate to the carboxylic acid-phosphoric acid mixed anhydride, 1,3-bisphosphoglycerate (which can be hydrolyzed to the corresponding carboxyhc acid and phosphoric acid). Start in a clockwise direction from the npper left.

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