DIRECT ELECTROCHEMISTRY OF NITRITE REDUCTASE FROM ACHROMOBACTER CYCLOCLASTES IAM-1013

The cyclic voltammetry of the nitrite reductase from Achromobacter cyc loclastes IAM 1013 exhibited well defined voltammetric response at a d i-4-pyridyl disulfide (4-pyds) modified gold electrode in the presence of A. cycloclastes apopseudoazurin. The midpoint potential, E(1/2), o f the native and type II copper-depleted (T2D) nitrite reductase obtai ned from the voltammogram were estimated to be 240 mV and 204 mV vs. N HE, respectively. The almost identical current value of the native and T2D reductase suggested that the voltammetric behavior contributed fr om the type 1 copper site. When nitrite was added into the nitrite red uctase solution (pH 7.0), an enhanced sigmoidal cathodic current-poten tial curve indicating the catalytic regeneration of oxidized nitrite r eductase was observed. The rate constant of nitrite reduction and the Michaelis constant, K-m, of the native reductase were estimated to be 5x10(2) mol(-1) dm(3) s(-1) and 7x10(-4) moldm(-3), respectively. The rate constant of the nitrite reduction and the K-m value of T2D nitrit e reductase were also estimated to be 1x10(2) mol(-1) dm(3) s(-1) and 3x10(-3) moldm(-3), respectively. These results suggested that the nit rite reduction activity is closely related with type II copper site.