Richards P G, Walton D J, Heptinstall J
School of Natural and Environmental Sciences, Coventry University, U.K.
Biochem J. 1996 Apr 15;315 ( Pt 2)(Pt 2):473-9. doi: 10.1042/bj3150473.
We have investigated the effects of tyrosine nitration (to form the weak acid, 3-nitrotyrosine) at positions 23 or 20 plus 23, on the structure and function of hen egg-white lysozyme. Enzyme activity against Micrococcus luteus cell-wall fragments or soluble substrates exhibits two phenomena. (a) A decrease in Km and kcat for the hydrolysis of soluble oligo- and poly-saccharides, resulting in only minor changes in the catalytic efficiency (kcat/Km) upon nitration. (b) The hydrolysis of M. luteus cell-wall fragments appeared to be dominated by electrostatic interactions with the protein, giving a decrease in enzyme activity as the 3-nitrotyrosyl group became ionized. Removal of the cell-wall anionic polymer, teichuronic acid, from M. luteus abolished this effect. The 3-nitrotyrosine group was also found to act as a fluorescence quencher of exposed tryptophan residues in lysozyme.
我们研究了在23位或20位加23位发生酪氨酸硝化（形成弱酸3 - 硝基酪氨酸）对鸡蛋清溶菌酶的结构和功能的影响。针对藤黄微球菌细胞壁片段或可溶性底物的酶活性表现出两种现象。(a) 硝化后，水解可溶性寡糖和多糖的Km和kcat降低，催化效率（kcat/Km）仅发生微小变化。(b) 藤黄微球菌细胞壁片段的水解似乎主要由与蛋白质的静电相互作用主导，随着3 - 硝基酪氨酸基团离子化，酶活性降低。从藤黄微球菌中去除细胞壁阴离子聚合物磷壁酸可消除这种影响。还发现3 - 硝基酪氨酸基团可作为溶菌酶中暴露的色氨酸残基的荧光猝灭剂。
