Monosaccharides, enzyme stabilization

Summarizing the results of many investigations, monosaccharides and such derivatives as D-mannitol and D-glucitol are rather weak acceptors. Disaccharides, including such acceptor products as isomaltose, are much better acceptors, except for certain molecules, for instance leucrose, which is not an acceptor.29,46,47 The decrease of enzyme activity with time has been described in terms of a first-order reaction. The inactivation parameters have been calculated for the immobilized enzyme. The inactivation constants kd were 0.0135 (1/d) when maltose was the acceptor (stabilizing), and 0.029 (1/d) when fructose was the acceptor.38... 

The factors influencing enzyme activity are discussed in such textbooks as those already mentioned, but may be summarized here. Briefly, use of any enzyme should be restricted to a temperature below that causing inactivation. The pH at which the enzyme is used should be such that the enzyme is both active and stable this can only be ascertained by studying the pH-stability and pH-activity properties of the enzyme. The matter of stability is particularly important when incubations are to be prolonged. Care must be taken when enzymes having alkaline pH requirements are used, becairse, under such conditions, alkali-catalyzed epimeri-zation of monosaccharide residues may take place, particularly if heat treatment is employed for enzyme inactivation. 

These findings, furthermore, offer a new explanation that does not rely on the questioned stereoelectronic effect as to why enzymes may change the conformation of a monosaccharide s unit or possibly preferentially stabilize the 6-OH in the gg orientation 87 (06-C6-C5-05) to make the substrate more reactive (Fig. 5.26). 

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