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 i ncorporated protein hemoglobin (Hb). Cyclic voltammetry of Hb-AQ films show ed 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 electro des was greatly facilitated in the AQ films. Soret absorption band position s suggest that Hb retains a near native conformation in AQ films in the med ium 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 transfe r in the electrochemical reaction. Square wave voltammograms of Hb-AQ films were fit by nonlinear regression analysis using a model featuring dispersi on of formal potentials. Hb can act as an enzyme-like catalyst in these fil ms as demonstrated by catalytic reduction of trichloroacetic acid with sign ificant decreases in the electrode potential required. (C) 1999 Elsevier Sc ience S.A. All rights reserved.