目的　研究化学修饰剂对N 乙酰氨基葡萄糖转移酶Ⅲ和Ⅴ活性的影响以探讨这两种酶的必需基团。方法　采用七种化学修饰剂分别修饰N 乙酰氨基葡萄糖转移酶Ⅲ和Ⅴ中的一些基团 ,用高效液相法测定酶的活性。结果　巯基、羧基、吲哚基和胍基被修饰后 ,N 乙酰氨基葡萄糖转移酶Ⅲ活性丧失 ,而氨基、羧基和吲哚基被修饰后 ,N 乙酰氨基葡萄糖转移酶Ⅴ活性丧失。结论　结果表明羧基、吲哚基和胍基是N 乙酰氨基葡萄糖转移酶Ⅲ的必需基团 ;氨基、羧基和吲哚基是N 乙酰氨基葡萄糖转移酶Ⅴ的必需基团。根据结果可推测羧基、吲哚基可能与酶的底物结合部位有关 ,而胍基、氨基分别是N 乙酰氨基葡萄糖转移酶Ⅲ和Ⅴ的催化部位必需的 Objective To study the effects of chemical modifiers on the activities of N-acetylglucosaminyltransferases Ⅲ and Ⅴ to explore the essential groups of these two enzymes. Methods Seven kinds of chemical modifiers were used to modify some groups of N and N-acetylglucosaminyltransferases Ⅲ and Ⅴ, respectively. The activity of the enzyme was determined by HPLC. Results The activity of N-acetylglucosaminyltransferase III was abolished after the sulfhydryl, carboxyl, indolyl and guanidino groups were modified, while the activity of N-acetylglucosaminyltransferase V was lost after the amino, carboxyl and indolyl groups were modified. Conclusion The results show that carboxyl, indole and guanidino are essential groups for N-acetylglucosaminyltransferase III; amino, carboxy and indolyl are essential groups for N-acetylglucosaminyltransferase V. Based on the results, it is speculated that the carboxyl group may be related to the substrate binding site of the enzyme, whereas the guanidine group and the amino group are necessary for the catalytic sites of N-acetylglucosaminyltransferases III and V, respectively