赖氨酸和精氨酸对三种离子强度下罗非鱼肌球蛋白溶解度及构象的影响

Effect of L-lysine and L-arginine on Solubility and Conformation of Tilapia Myosin at Three Ionic Strengths

摘要:

本研究以罗非鱼肉为原料，提取肌球蛋白，选取三种代表性的盐浓度，分别采用10 mmol/L的赖氨酸（L-lysine）和精氨酸（L-arginine）溶液对其进行透析处理，探讨氨基酸对低离子强度下肌球蛋白增溶行为的影响。结果显示：在实验范围内，肌球蛋白的溶解度随离子强度的增加而增大（p<0.05）；氨基酸对高离子强度（600 mmol/L KCl）条件下肌球蛋白的溶解度、浊度及二级结构的影响较小；低离子强度（1 mmol/L KCl）条件下，赖氨酸和精氨酸能抑制肌球蛋白纤丝形成，降低体系的浊度，增溶效果明显，增溶后α-螺旋含量增加（p<0.05）；生理离子强度（150 mmol/L KCl）条件下，体系的浊度明显下降，溶解度增加，表面疏水性增大，α-螺旋含量下降（p<0.05），丝状体完全解离，体系更加分散；初步分析赖氨酸和精氨酸诱导低离子强度下肌球蛋白增溶的原因可能与体系pH值的变化及对蛋白质分子间静电相互作用的影响有关。

Abstract:

Myosin was extracted from tilapia (Oreochromis niloticus) muscle, and 5.0 mg/mL myosin was dialyzed against three ionic strengths of a solution containing 10 mmol/L L-lysine and L-arginine. Effect of amino acid on solubilization of myosin was investigated at different ionic strengths. The solubility of myosin increased with increasing ionic strength (p<0.05). In a high-ionic-strength (600 mmol/L KCl) solution, little effect of L-lysine and L-arginine was detected on solubility, turbidity, and secondary structure on tilapia myosin. In a low-ionic-strength (1 mmol/L KCl) solution, the presence of L-lysine and L-arginine inhibited formation of myosin filament, and caused a decrease in turbidity, significantly increased solubility, accompanied by a significant increase in α-helix content of solubilized myosin. Nevertheless, in a physiological-ionic-strength (0.15 mol/L KCl) solution, a decrease in turbidity and increase in solubility of tilapia myosin was detected, accompanied by a significant increase in surface hydrophobicity (p<0.05) and loss of α-helix content. The myosin filament was completely depolymerized, and the protein system was more dispersed at physiological ionic strength with L-lysine and L-arginine. The results indicated that L-lysine and L-arginine changed the pH of myosin solution because of a specific role in disrupting electrostatic interactions, which resulted in the solubilization of myosin at low ionic strength.