Electrochemical studies of albumin-heme hybrid in aqueous media by modified electrode

The electrochemical properties of a synthetic hemoprotein, recombinant human serum albumin (rHSA) incorporating 2-[8-{N-(2-methylimidazolyl)}octanoyloxymethyl]-5,10,15,20-tetrakis(alpha,alpha,alpha,alpha -o-pivalamidophenyl)porphinatoiron(II) (FeP) (rHSA-FeP), in aqueous media were investigated using an edge plane pyrolytic graphite electrode modified with didodecyldimethylammonium bromide. The redox behavior of the rHSA-FeP hybrid fits well with thin-film electrochemistry: (1) the redox potential (E-1/2) of the Fe(III)/Fe(II) couple in the hybrid was always constant; however, (2) the peak current and separation increased depending on the scan rate. Because the isoelectric point (pl) of rHSA-FeP is 4.8, its electron density becomes higher with an increase in pH of the aqueous solution (pH 4-9) and the E-1/2 shifts to the anodic side. The counter anions and their concentration affect the E-1/2, suggesting that the counter anions participate in the redox reaction. Compared with that of the naked FeP in aqueous solution, the E-1/2 of rHSA-FeP shifts in the cathodic direction. This indicates that the hydrophobic environment in the albumin host makes the Fe(H) state difficult to oxidize. An increase in the number of the combined FeP molecule(s) in rHSA from 1 to 4 and 8 results in a positive shift of the E-1/2. The first bound FeP probably sits at the outer domain of the albumin structure, and the other seven FeP molecules are in a relatively inner position. (C) 2001 Published by Elsevier Science BN.