KINETIC-STUDIES ON THE ELECTRON-TRANSFER BETWEEN VARIOUS C-TYPE CYTOCHROMES AND IRON(III) USING A VOLTAMMETRIC APPROACH

Cyclic voltammetry was used here to investigate the kinetics of the el ectron transfer between a soluble iron(III) complex and several cytoch romes isolated from Desulfovibrio and Desulfuromonas species. The seco nd order rate constants were calculated and found to be in the 10(5)-1 0(6) M-1 s(-1) range. Their values are discussed from the point of vie w of the redox potentials, heme content and pi value of the proteins. The ability of poly(ester-sulfonic acid) ionomer (Eastman AQ-29D) to e ntrap positively charged cytochromes made it possible to study the imm obilized proteins. When the cytochromes are incorporated into this pol ymer matrix, diffusion limitations lead to a 50 times lower catalytic efficiency as compared to catalysis with protein in solution. The resu lts of this study demonstrate that only cytochromes with bishistidinyl heme iron coordination act as metal reducers whereas mitochondrial c- type cytochromes do not. This approach opens new pathways for the use of sulfur and sulfate reducing bacteria in the bioremediation of metal contaminated waters and waste streams. Processes involving the use of entrapped enzymes reactors could be developed according to the metal reducing activity of their polyhemic c-type cytochromes. (C) 1998 Else vier Science Ltd. All rights reserved.