engleski

Electrochemical studies of the effect of temperature on the adsorption of yeast alcohol dehydrogenase at Pt

The interfacial behaviour of Yeast Alcohol Dehydrogenase (YADH) without and with the coenzyme nicotinamide adenine dinucleotide (NADH-YADH) at a Pt surface was studied over the temperature range 273 to 353 K in a phosphate buffer solution pH 7.0, using cyclic voltammetry and electrochemical impedance spectroscopy. It was shown that the surface charge density and corresponding polarization resistance, resulting from protein adsorption and its oxidation, respectively, is directly proportional to the amount of adsorbed protein (surface concentration), indicating that adsorption at anodic potentials is accompanied by the transfer of charge, i.e. chemisorption through acidic carboxylate groups on the protein. The adsorption process for both proteins was described with the Langmuir adsorption isotherm, which revealed very high affinity of the proteins towards adsorption onto a Pt surface. From the calculated Gibbs energies of adsorption it was concluded that both proteins strongly adsorb onto the Pt surface via chemisorption. The adsorption process for YADH was found to be exothermic. However, the adsorption of NADH-YADH resulted in an endothermic adsorption process as a result of the presence of the coenzyme, nicotinamide adenine dinucleotide (NAD^+/NADH), in NADH-YADH which stabilizes the protein against denaturation. However, the adsorption of both proteins was found to be an entropically governed process, suggesting structural unfolding of the proteins at the electrode surface. The maximum surface concentration values indicate that there is no significant difference in the amount of adsorbed proteins between YADH and NADH-YADH in the whole temperature range investigated.

adsorption; proteins; YADH; NADH-YADH; electrochemical studies

nije evidentirano