Trypsin mimic

The outstanding inclusion ability and the carboxylic functions of host I raised the idea of co-erystallizing it with imidazole (Im) which, due to its versatile nature 114), is one of the frequently used components in enzyme active sites, generally presented by histidine. Formally, a system made of imidazole and an acid component may mimic two essential components of the so-called catalytic triad of the serine protease family of enzymes the acid function of Aspl02 and the imidazole nucleus of His57 115) (trypsin sequence numbering). The third (albeit essential) component of the triad corresponding to the alcohol function of Seri 95 was not considered in this attempt. This family of enzymes is of prime importance in metabolitic processes. 

Inorganic mimic of catalase was prepared according to the well-known technique [5], Partly purified catalase of human blood erythrocytes and trypsine (Sigma Company) were used for the catalase sources. 

A monoclonal antibody which reacts with an epitope within the M domain has recently been used to check whether it influences the receptor s DNA binding properties [65]. The immune complex with wild-type receptors was indeed found to chromatograph on DNA-cellulose similar to nt1 mutant receptors or the chymo-trypsin-degraded wild-type. Reaction with the antibody mimics the removal of the M domain which suggests that biochemical modifications of the M domain could... 

This Highlight is part of an extraordinary story (also a cautionary tale) in the area of biocatalysis. The point of particular interest was the incredible catalytic activity claimed for so-called pepzymes - small synthetic peptides modelled to mimic the active site structures of trypsin and chymotrypsin. One was claimed to hydrolyse a simple peptide (a trypsin substrate) with efficiency comparable to that of the native enzyme. This extraordinary result provoked at least as much scepticism as excitement, and in the following months several groups tried to reproduce the results. They failed, comprehensively. [1,2] Some reasons why this failure came as no surprise were subsequently summarised by Matthews, Craik and Neurath, [3] and by Corey and Corey [4]. The background has been discussed in an Angewandte Review on Enzyme Mechanisms, Models and Mimics. [5]... 

For example, a superb mimic of the charge-relay system in serine proteases has been prepared by attaching both carboxylate and imidazole to a-, fi-, and y-CyDs [24]. The hydroxy group, the last component of the charge-relay system, is provided by the CyDs. The activity (kinetic parameters) of the -CyD-based artificial enzyme for ester hydrolysis is close to that of aartificial enzymes show acylation, deacylation, and turnover, as is observed in the reactions of chymo-trypsin. The substrate-specificity is dependent on the kind of CyD used, since it is primarily governed by the substrate-binding process. In phenyl ester hydrolysis, a- and yS-CyD-based artificial enzymes are better than the y-CyD-based artificial enzyme. For the hydrolysis of tryptophan ethyl ester, however, the y-CyD-based artificial enzyme is the best. In another serine protease model, tripeptide (Ser-His-Asp) is directly introduced to the primary hydroxyl side of f -CyD [25]. This... 

The tosyl-phenylalanine moiety mimics a substrate like N-tosyl-phenyl-alanine methyl ester and the chloroketone function (see Section 2.3) acts as an electrophile where the chloride ion is displaced by His-57 at the active site of the enzyme. Similarly, a chloromethylketone analogue of lysine inhibits trypsin. 

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