Hydrolase concept

Many so-called glycoside hydrolases catalyze some glycosyl transfer to acceptors other than water. However, it has always been assumed that carbohydrases which have strictly or predominantly hydrolytic action on one substrate would necessarily prove solely or predominantly hydrolytic with all utilizable (suitably diluted) substrates. This is the essential assumption of the hydrolase concept it is not made by the glycosylation model, and it is this assumption which our experimental findings, as well as theoretical base, deny. 

In this case the predominance of glycosylation of C4-carbinols over substrate hydrolysis is in a mixture where the molar concentration of water was more than 3000 times that of the a-maltosyl fluoride. In other experiments the substrate concentration could be further reduced at least 5-fold without altering the fact of a substantially greater extent of maltosidic linkage synthesis than hydrolysis. We now are referring to a very dilute 4 mM, solution of substrate with which, if the hydrolase concept were valid, hydrolysis ought to have been predominant. 

W. Nerinckx, T. Desmet, K. Piens, and M. Claeyssens, An elaboration on the syn-anti proton donor concept of glycoside hydrolases. Electrostatic stabilisation of the transition state as a general strategy,... 

Williams et al. have now demonstrated the compatibility of enzyme and transition metal complexes in one reaction vessel. Two examples illustrate the concept first a palladium-catalyzed racemization f9J of an allylic acetate in the presence of a hydrolase (Scheme 1), and second the racemization of a secondary alcohol [10] through Oppenauer oxidation / Meerwein-Ponn-dorf-Verley reduction with concomitant acylation of one enantiomer with a lipase from Pseudomonas fluorescens (Scheme 2). 

In keeping with the concept of the RIP discussed under Relative Inhibitory Potency , above, inhibition of lymphocyte and/or platelet NTE and possibly erythrocyte LysoPC hydrolase should be used in conjunction with inhibition of erythrocyte AChE and plasma butyryl-cholinesterase (BChE) to assess the likelihood that an exposure to OP compounds would produce cholinergic and/ or delayed neuropathic effects. Erythrocyte AChE inhibition has long been used as a biomarker of exposure to conventional nerve agents or OP insecticides (Lotti, 1995 Wilson and Henderson, 1992). BChE can be sensitive to both conventional and DN agents, and its inhibition could thus serve as a general biomarker for OP agents (Kropp and Richardson, 2007 Van der Schans et al, 2008). 

The most frequently applied concepts for the enzymatic formation of oligosaccharides and glycoproteins involve the utilization of glycosyl transferases or exo- and e do-glycosyl hydrolases (glycosidases) [58]. Glycosyl transferases require expensive and often unstable sugar nucleotides as activated donor substrates, a major problem besides the poor availability of the enzymes. However, trans-... 

The concept of electrostatic catalysis has been applied indirectly by Schramm and coworkers for the design of transition-state analogues in reactions by nucleoside hydrolase (Horenstein et al., 1991 Horenstein and Schramm, 1993) and AMP deaminase (Kline and Schramm, 1994). They stated, in accordance with our previous examples, that the MEP provides novel insight into transition-state structure and the forces associated with substrate binding and release. 

After the initial discovery that 0-fluoromethylene-substituted amines (e.g., 184, Table 1) were potent, mechanism-based inhibitors of monoamine oxidase (MAO) (41), the concept was successfully broadened to include most of the common amine oxidases (Table 1). This approach was also used to design inhibitors of y-aminobutyric acid transaminase both the a- and 0- substituted amino acids 189 and 190 were found to inactivate this enzyme. Recently, applica-tion of this concept to the design of inhibitors of S-adenosyl-homocysteine hydrolase (SAH) has led to the discovery of very potent inhibitors of this enzyme (e.g., 176, Table 1). 

Certain properties of lysozyme, which are common to / -glucan endo-hydrolases, have been explained following the elucidation of the structure of the active site. It is therefore relevant to discuss the current concepts of lysozyme structure and action and to compare these with the rather fragmentary observations so far made on the action of the various / -glucan endo-hydrolases. 

Up to now the practical application of biosensors has been almost entirely limited to oxidase-based amperometric monoenzyme electrodes and pH-shifting by hydrolases. However, the internal coupling of different biocatalytic reactions in biosensors will lead to a greatly extended applicability and a substantial improvement of the analytical performance characteristics. Exciting results might be achieved by applying the concepts of chemical and genetic modification of enzymes. Further, the site-to-site directed fixation of artificially coupled enzymes could improve the speed and practicability of coupled substrate conversions. 

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