Effects of Chemical Modification of Lysine, Tyrosine and Tryptophan Residues in Pea Seed Nucleoside Diphosphate Kinase and Inhibition of the Enzyme with Antibodies

Abstract

Pea seed nucleoside diphosphate kinase (NDP kinase) is an oligomeric, tetrameric enzyme which has been shown to be phosphorylated by its substrate ATP, presumably forming an l-phosphohistidine at its active site. Recently has also a reactive lysine residue been demonstrated at the active site. In the present investigation nitration of a tyrosine residue is shown to inactivate the enzyme. There seems only to be a slight structural change in the enzyme on modification of these essential lysine and tyrosine residues, since double diffusion experiments with an inhibitory antiserum shows no difference in reactivity between the native enzyme and the modified enzyme. It is also found that modification of all tryptophan residues in the enzyme reduces the enzyme activity only to a small degree, indication that these hydrophobic amino acid residues are not directly involved in the catalytic process.