| dc.description.abstract | The above detailed account of the role of various groups in enzyme function amply illustrates the approaches to the study of the structural basis of enzyme action. One particular fact emerges out of the present account. Whenever a specific reagent is available for a group and its reaction with the group can be easily quantitated, the study of that group has been very wide. This applies chiefly to sulphydryl and amino groups. More enzymes are studied by modifying these groups than all the other groups put together. This does not imply that the other groups do not have a significant role in action. For example, in spite of their charge, the carboxyl and phenolic groups have not been paid sufficient attention to, due to the lack of mild reagents and rapid quantitation procedures. In the same way, there is no reason to believe that the so-called “unreactive” side chains of phenylalanine, methionine, leucine, isoleucine or valine do not have a role in enzyme action merely on the grounds of non-availability of specific reagents.
But as Bier has pointed out, it is always necessary to check if the loss of activity is due to change in conformation of the enzyme resulting from chemical modification, or if the group per se has a role in catalysis. By using bulkier acid anhydrides for the acylation of trypsin, substitution could be restricted to a single amino group to give an inactive product, suggesting the important role of this group in the activity of trypsin.
If a type of group is to be implicated, it is necessary to demonstrate that modification of one or two groups should cause a large decrease in activity. It is pertinent to cite the study of Hirs and Halman where arylation of only one amino group inactivated RNase. The modified group might be necessary for activity as in the case of the methionine residue of RNase.
Aim and Scope of the Investigation on Lysozyme
With the availability of sequences of a few more enzymes, it is certain that all effort will be marshalled to relate the chemical modification of a particular group to the loss of activity. This is already being attempted on ribonuclease. Lysozyme, with a slightly higher molecular weight than RNase, has also been analysed in detail for sequence and forms a suitable choice for similar studies. Though many group modifications are studied with this enzyme, the tryptophan groups are not studied. The following chapter contains the results of experiments where the tryptophan groups are modified using NBS to study the role of these groups in the activity of lysozyme. It has been clearly established that tryptophan residues do have a role in the action of this enzyme and the conformation changes are not significant during tryptophan oxidation. It is hoped that these results will help to understand the role of tryptophans in the mechanism of action of enzymes and particularly of lysozyme. | |
