The effects of tyrosine nitration on the structure and function of hen egg-white lysozyme.
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.
Richards
P G
PG
School of Natural and Environmental Sciences, Coventry University, U.K.
Walton
D J
DJ
Heptinstall
J
J
D000818:Animals; D002473:Cell Wall / Q000737:chemistry; D002645:Chickens; D004563:Electrochemistry; D005260:Female; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D016982:Micrococcus luteus / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009113:Muramidase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009566:Nitrates / Q000737:chemistry; D010063:Ovum / Q000201:enzymology; D017354:Point Mutation; D011487:Protein Conformation; D013379:Substrate Specificity; D014443:Tyrosine / Q000737:chemistry
D009566:Nitrates; D014443:Tyrosine; D009113:Muramidase