Enzymes amidase, action

As illustrated in Figure A8.3 nitrilases catalyse conversions of nitriles directly into the corresponding carboxylic adds (route A), while other nitrile converting enzymes, die nitrile hydratases, catalyse the conversion of nitriles into amides (route B) which, by the action of amidases usually present in the whole cell preparations, are readily transformed into carboxylic adds (route C). 

The anomalous behaviour observed in attempted 1-deprotection of certain 4-heteroarylmethyl-l-(4-methoxyphenyl)-2-azetidinones by the action of CAN has been investigated further <961771 > and evidence obtained to support the mechanism proposed, which involves the intermediate 47 when the 4-substituent is the tetrazolylmethyl group as in 46 <96T10169>. Use of the novel enzyme, o-phthalyl amidase, as a deprotection agent for P-lactams has been developed <96MI875>. 

The use of enzymes and whole cells as catalysts in organic chemistry is described. Emphasis is put on the chemical reactions and the importance of providing enantiopure synthons. In particular kinetics of resolution is in focus. Among the topics covered are enzyme classification, structure and mechanism of action of enzymes. Examples are given on the use of hydrolytic enzymes such as esterases, proteases, lipases, epoxide hydrolases, acylases and amidases both in aqueous and low-water media. Reductions and oxidations are treated both using whole cells and pure enzymes. Moreover, use of enzymes in sngar chemistiy and to prodnce amino acids and peptides are discnssed. 

The types of enzymes that bring about hydrolysis are hydrolase enzymes. Like most enzymes involved in the metabolism of xenobiotic compounds, hydrolase enzymes occur prominently in the liver. They also occur in tissue lining the intestines, nervous tissue, blood plasma, the kidney, and muscle tissue. Enzymes that enable the hydrolysis of esters are called esterases, and those that hydrolyze amides are amidases. Aromatic esters are hydrolyzed by the action of aryl esterases and alkyl esters by aliphatic esterases. Hydrolysis products of xenobiotic compounds may be either more or less toxic than the parent compounds. 

This suggests that the creation of novel enzyme specificity has a high probability if a closely related catalytic machinery and/or architecture is present for both types of activities, i.e. both substrates should be converted by the Ser-His-Asp triad present in lipases and amidases if an amidase substrate should be accepted by a lipase or vice versa. The chance for creating activity is usually enhanced if both enzymes share high sequence and/or structural homology. In other words, most readers will agree that it will be rather impossible to convert an esterase into a monooxygenase as these two enzymes differ substantially in their architecture, substrate and cofactor-requirement and consequently mode of action. 

The enzymatic hydrolysis of a broad range of nitriles to the corresponding amides and acids is documented [35]. These conversions are effected directly by nitrilases or by successive action of a nitrile hydratase and an amidase. Most of these enzymes are usually unstable and whole-cell preparations are preferred. However, recently a purified nitrile hydratase preparation without amidase activity was shown to convert several 2-arylpropionitriles enantioselectively to the corresponding optically active amides (eq. (3)) [36]. 

It is still to be noted that the butyro-amidase does not furnish the reaction ordinarily found when the experiment takes place in the presence of bacteria which secrete the enzyme. We succeed in the latter case, with the living ferment, in deamidizing up to 96 per cent of the total nitrogen contained in the products of the proteolysis. Now the enzymes isolated from their bacteria react solely on certain substances which form only about I of the total weight. Butyro-amidase reacts in two different ways on asparagin, according to the conditions of the medium. With water alone, as seen above, the action is limited to the amide grouping. On the contrary, in the presence of... 

The putrefactive bacteria, which obviously must have acted in former times as they do at present, secrete proteolytic enzymes as well as amidases. In succession, these various enzymes exerted their action on the nitrogenous materials of marine animals to give finally, among numerous derivatives, volatile fatty adds, of which some were endowed with a rotatory power. These optically active substances, mixed with fats which had resisted bacterial decomposition, and subjected to the combined action of a high temperature and a strong pressure, formed the natural petroleums. 

From the preceding, it should be remembered that tyrosin, phenylalanin, tryptophane, and the amino-acids substances that remain unchanged in he hydrol3 es realized by the digestive enzymes, are, on the contrary, the substances which are the most easily transformed in putrefactions, since they give rise to numerous derivatives, oxyacids, indol, and phenols. One of the characteristics of the action o the amidases secreted by the putrefactive bacteria appears to be the fact that they address themselves preferably to the aromatic substances which have come from proteolysis. 

Kashiwagi M, Fuhshuku K-1, Sugai T (2004) Control of the nitrile-hydrolyzing enzyme activity in Rhodococcus rhodochrous IFO 15564 preferential action of nitrile hydratase and amidase depending on the reaction condition factors and its application to the one-pot preparation of amides from aldehydes. J Mol Catal B Enzym 29(l-6) 249-258... 

Among stereoselective nitrile-converting enzymes, the combined action of a stereoselective nitrile hydratase and a stereoselective amidase has been often described, and stereospecific nitrile conversions by whole cells are frequently found in the patent literature [59,60] however, careful analysis has usually revealed stereoselectivity in the amidase and not or only to a low extent in the hydratase [61,62]. If both enzymes were stereosj ific, nitrile hydratase and amidase have been described to act either synergistically or antagonistically regarding their enantioselectivity. 

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