Enhanced electron transfer for hemoglobin in poly (ester sulfonic acid) films on pyrolytic graphite electrodes

Stable films made from the ionomer poly (ester sulfonic acid) Eastman AQ55 on pyrolytic graphite (PG) electrodes gave reversible voltammetry for the incorporated protein hemoglobin (Hb). Cyclic voltammetry of Hb-AQ films showed a pair of well-defined, reversible peaks at about - 0.04 V versus SHE at pH 5.5. Compared to solutions, electron transfer between Hb and PG electrodes was greatly facilitated in the AQ films. Soret absorption band positions suggest that Hb retains a near native conformation in AQ films in the medium pH range. The formal potential of the Hb heme Fe(III)/Fe(II) couple in AQ films shifted linearly between pH 4 and 11 with a slope of - 52 mV pH (-1), suggesting that one proton transfer is coupled to each electron transfer in the electrochemical reaction. Square wave voltammograms of Hb-AQ films were fit by nonlinear regression analysis using a model featuring dispersion of formal potentials. Hb can act as an enzyme-like catalyst in these films as demonstrated by catalytic reduction of trichloroacetic acid with significant decreases in the electrode potential required. (C) 1999 Elsevier Science S.A. All rights reserved.