Voltammetric study of the adsorbed thermophilic plastocyanin from Phormidium laminosum up to 90 °C

Abstract

Redox thermodynamics and kinetics of plastocyanin from Phormidium laminosum, and of azurin from Pseudonomas aeruginosa, have been investigated as a function of temperature by protein film voltammetry. To this purpose, both proteins have been physisorbed on a pyrolytic graphite edge electrode. A pronounced negative shift of the plastocyanin standard potential, compared to a slight shift in the case of azurin, has been found upon increasing the temperature. Hence, significant conformational and/or solvation changes accompany the redox conversion of plastocyanin. Lower electron transfer rate constants (by c.a. one order of magnitude) and higher activation enthalpies have been found for plastocyanin as compared to azurin. The voltammetric response of azurin vanishes irreversibly at temperatures close to 60°C, whereas the redox properties of plastocyanin remain unaltered, except for some loss of electroactive protein, after heating the electrode at temperatures as high as 90°C.