低盐条件下SDS对罗非鱼肌球蛋白热聚集的抑制及其机理

Inhibition and Mechanism of SDS on Thermal Aggregation of Tilapia Myosin at Low Salt Concentrations

【目的】探讨十二烷基硫酸钠(sodium dodecyl sulfate,SDS)对低盐条件下肌球蛋白热聚集的抑制效果及机理。【方法】提取罗非鱼(Oreochromis niloticus)肌球蛋白,比较精氨酸、蔗糖和SDS对肌球蛋白热聚集的抑制效果,确定添加3 mmol/L的SDS,进一步分析0~150 mmol/L KCl的低盐条件下,热处理(50℃,30 min)对肌球蛋白体系浊度、溶解度、分子结构及粒度分布的影响。【结果】在实验盐浓度范围内,肌球蛋白溶解性差,体系浑浊,经热处理后溶解度明显下降(P <0.05),表面疏水性增大,α-螺旋含量减小(P <0.05),肌球蛋白分子热变性聚集明显;添加SDS后,表面疏水性增大(P<0.05),微量SDS与肌球蛋白产生特异性结合,导致纤丝解离,分子间静电斥力增加,平均粒径减小(P <0.05),在1~100 mmol/L KCl范围内溶解度明显增大(P <0.05),SDS对肌球蛋白的增溶效果明显;SDS-肌球蛋白亲水复合体经热处理后分子进一步展开,表面疏水性明显增大(P<0.05),体系仍然澄清透明,分子间无明显的热聚集。【结论】SDS可抑制肌球蛋白的热聚集,其抑制机理与低离子强度下SDS与蛋白分子间通过静电和疏水相互作用结合导致肌球蛋白纤丝解离有关。

【Objective】To study the inhibitory effect and mechanism of sodium dodecyl sulfate(SDS)on the thermal aggregation of myosin under low salt condition.【Methods】Myosin was extracted from tilapia(Oreochromis niloticus)muscle,and sucrose,L-arginine,and SDS were added to the myosin dispersion followed by heating at 50℃for 30 min,and the inhibitory effect on the thermal aggregation of myosin was compared.Comparative experiments determined that 3 mmol/L SDS was added in further study,and the effect of SDS on heat-induced aggregation of myosin was investigated in terms of turbidity,solubility,molecular structure and particle size distribution at low KCl concentrations from 1 to 150 mmol/L.【Results】In low salt concentrations,there was poor solubility and turbid solution of myosin.After heating at 50℃for 30 min,the myosin dispersion exhibited significant thermal denaturation and aggregation as showed by a significant decrease in the solubility(P<0.05),and this was accompanied by an increase of surface hydrophobicity and loss ofα-helix content(P<0.05).However,addition of 3 mmol/L SDS promoted a specific role between SDS and protein molecules,and resulted in the depolymerization of myosin filament,surface hydrophobicity of myosin monomer increased significantly(P<0.05)and electrostatic repulsion between molecules was enhanced.As compared to unheated myosin,the average particle size of myosin significantly decreased(P<0.05)and the solubility increased significantly(P<0.05),which indicated solubilization effect of myosin by SDS in 1-100 mmol/L KCl solution.Even after heat treatment,the hydrophilic SDS-myosin complex solution was still clear and transparent with further unfolding and increased surface hydrophobicity(P<0.05),which indicated there was no significant thermal aggregation among the myosin molecules.【Conclusion】SDS can suppress the thermal aggregation of myosin at low salt concentrations,and the mechanism of the inhibitory is related to the depolymerization of myosin filament due to a specific role between SDS and protein molecules through electrostatic and hydrophobic interactions.