Protection of ovalbumin against irreversible heat denaturation by a cationic amphiphile at high concentration

Abstract

SummaryThe interaction of the cationic amphiphile cetylpyridinium chloride (CPC) with the egg white protein ovalbumin, was studied at various temperatures and pH values. The influence of different concentrations of CPC on the thermal behaviour of the protein was followed by specific optical rotation measurements in the pH interval 3‐9. No increase in optical rotation was found at any pH when CPC was added to ovalbumin at room temperature. When heated, a gradual increase in optical rotation was registered, which became smaller the higher the pH used. At molar ratios of CPC :ovalbumin of above 70 this increase was reversed on cooling. The reversibility of the thermal unfolding on cooling was not affected by a variation in protein concentration between 0.5 and 10%. Circular dichroism measurements before and after a heating‐cooling cycle confirmed the results obtained on optical rotation. When CPC was exchanged against the anionic amphiphile, sodium dodecylsulphate (SDS), a denaturing effect was achieved at neutral and alkaline pH values already at room temperature. At the acidic side of the isoelectric point, however, there was no major effect of SDS. No thermal aggregation of ovalbumin occurred near the isoelectric point when CPC was present and complete resolubility was found after thermal treatment and drying.