拟康氏木霉中内切葡聚糖苷水解酶的化学修饰

动力学研究揭示两个pK值为4.4和5.8的氨基酸残基可能对内切酶活性起重要作用，化学修饰研究结果表明一个羧基氨基酸对内切葡聚糖苷水解酶活力为必需的，且可能位于或接近酶的催化位点．

Chemical Modification of Endoglucanase I from Trichoderma pseudokiningii S-38:Evidence for Essential Carboxyl Group

The role of carboxyl group in the catalytic action of endoglucanase I (Mr 70 2000)from Trichoderma paseudokiningii S-38 was delineated through chemical modification using Woodword reagent K and kinetic studies. The pH profile gave the kinetic apparent pK values of 4. 2 and 5. 8 for free enzyme and 3. 7 and 5. 5 for enzyme-substrate complex, respectively. The kinetic of inactivation indicated that one carboxyl residue was essectial for the enzyme with a second order rate constant of 395 min/mol. The kinetic analysis of the WRK modified enzyme gave valuse of Km similar to that of native enzyme. but Kcat values was lower. It indicated that the catalytic hydrolysis and not the substrate binding was affected by chemical modification. Treatment of the enzyme with diethyl pyrocarbonate reslted in the modification of 3. 2 residues of 3. 5 histidyl residues with the retention of 92% of the original enzymatic activity. Tritation of the enzyme with dithiobis (2-nitrobenzoic acid) showed only one free sulfhydryl group and five disufide inkages present in the enayme. and 10% loss of activity was observed when the free sulfhydrl group was modified. Reaction with tetranitromethane did not affect any of the enzymatic activity.