A Blue Protein as an Inactivating Factor for Nitrite Reductase from Alcaligenes faecalis Strain S-6

Abstract

A blue protein with a molecular weight of 12, 000 containing 1 atom of type I Cu²⁺ was purified and crystallized from a denitrifying bacterium, Alcaligenes faecalis strain S-6, as an inactivating factor for copper-containing nitrite reductase of the same organism. Inactivation of the enzyme occurred when the enzyme was incubated aerobically with a catalytic amount of the blue protein in the presence of reducing agents such as cysteine and ascorbate. The blue protein acts as a direct electron donor for the enzyme to catalyze the reduction of nitrite, but in the absence of nitrite, the enzyme-reduced blue protein system reacts with oxygen to produce H₂O₂. A suicide inactivation mechanism of the enzyme due to this H₂O₂ production is proposed.