Ca 2+ Affects Physicochemical and Conformational Changes of Threadfin Bream Myosin and Actin in a Setting Model

ABSTRACT: The effect of C a 2+ on physicochemical and confor mational changes of thr eadfin br eam ( TB) my osin andactin during setting at 25 and 40 °C was investigated. Ca 2+ ion at 10 to 100 mM induced the unfolding of myosin andactin as evident b y an incr ease of sur face hy drophobicity (S o ANS) at 40 °C. Total SH gr oups also decr eased with anincreased Ca 2+ concentration, suggesting that Ca promoted the formation of disulfide bonds during setting at 40 °C.Both hydrophobic interactions and disulfide linkages were involved in formation of myosin aggregates at 40 °C andwere enhanced b y addition of 10 to 100 mM C a 2+ . Myosin C a-ATPase activity decr eased when C a 2+ was gr eater than50 mM, indicating conformational changes of myosin head. Circular dichroism spectra demonstrated that Ca 2+ reduced the -helical content of myosin and actin incubated at either 25 or 40 °C. Ca 2+ induced conformationalchanges of TB myosin and actin incubated at 40 °C to a greater extent than at 25 °C.Keywords: threadfin bream, myosin, actin, calcium, setting

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