The effects of chemical modification on spinach nitrite reductase

It was demonstrated that chemical modification of spinach nitrite reductase with phenylglyoxal, pyridoxal-5'-phosphate, and N-bromosuccinimide eliminated the ferredoxin linked activity of the enzyme. It is believed that the former two reagents modify specific arginine and lysine residues, respectively, and thereby interfere with the electrostatic interaction between nitrite reductase and ferredoxin. The latter reagent, Nbromosuccinimide, is believed to modify a specific tryptophan which is needed to assist in the transfer of electrons fi"om the [2Fe-2S] cluster of ferredoxin to the [4Fe-4S] cluster of nitrite reductase. The purpose of this dissertation was to determine the arginine, lysine, and tryptophan residues necessary for nitrite reductase activity.

Chemical modification with [C] phenylglyoxal resulted in the identification of two arginine residues, R375 and R556, that appear to be located at the ferredoxinbinding site. Chemical modification with [^H] pyridoxal-5'-phosphate resulted in the indentification of one lysine residue at postion 437 that also appeared to be located at the ferredoxin-binding site of spinach nitrite reductase. These residues are likely to be involved in the electrostatic interaction between ferredoxin and the enzyme.

Modification of the enzyme with N-bromosuccinimide led to the identification of a tryptophan residue, W92, that appeared to be at the ferredoxin-binding site and suggested that it assists in the transfer of electrons from ferredoxin to nitrite reductase.