Site directed mutagenesis has been performed to test hypotheses concerning the putative active sites of Trichoderma reesci cellobiohydrolase I and endoglucanase I. It is shown that mutagenesis of the residue 1:126, previously proposed to be the proton donor in CBHI, did not totally inactive the enzyme while mutagenesis of the residue 1:127 in the homologous enzyme EG1 resulted in complete loss of activity. These results are compared with those obtained in similar studies of other glucanases and the effects on enzymatic activity of hyperglycosylation of the yeast produced cellulases are discussed.
