Conformational and rheological changes in catfish myosin during alkali-induced unfolding and refolding

Changes in the conformation of catfish (Ictalurus punctatus) myosin due to (i) cations (ii) alkaline pH and (iii) salt addition were determined using circular dichroism, tryptophan fluorescence, differential scanning calorimetry and hydrophobicity studies. The relation between conformation and storage modulus (G′) of alkali treated myosin was studied. Two types of bases, NaOH and KOH were used for unfolding myosin under three alkaline conditions, pH 11.0, 11.5 and 12.0. Myosin, unfolded under alkali conditions was immediately refolded by adjusting pH back to 7.3. Subjecting myosin to alkaline conditions and subsequent readjustment to pH 7.3 increased the G′ of thermally treated myosin. G′ was affected by the presence or absence of salt during alkali treatments. When salt was present during alkali unfolding of myosin, the added salt stabilized the conformation of myosin against alkali unfolding and denaturation. In the absence of salt or when salt was added after refolding, myosin showed significantly higher denaturation and high G′ on heating and cooling. Among the different alkaline pH values, myosin treated at pH 11.0 showed higher G′. The type of anions influenced the conformation of myosin and the strength of gels. Treatment of myosin with KOH resulted in greater denaturation and higher gelling ability (G′) compared to NaOH.