丙二醛氧化修饰对白鲢肌原纤维蛋白结构性质的影响

Effect of Malondialdehyde-Induced Protein Oxidation on Structural Properties of Myofibrillar Protein from Silver Carp(Hypophthalmichthys molitrix)

采用丙二醛模拟氧化体系研究脂肪氧化的次级产物小分子醛类对白鲢肌原纤维蛋白结构性质的影响。结果表明:丙二醛浓度范围在0.05~0.50 mmol/L内,肌原纤维蛋白的羰基和游离氨基含量变化不显著,活性巯基含量以及表面疏水性在丙二醛浓度为0.05~0.25 mmol/L范围内有所上升,二聚酪氨酸含量略有下降,Ca^2+-ATPase活性先下降后上升,溶解度随着丙二醛浓度上升而下降。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳图谱显示,氧化使蛋白质分子间发生了交联和聚集,二硫键是主要的交联方式。随着丙二醛浓度的上升,蛋白α-螺旋相对含量下降,β-折叠相对含量上升。结果表明以丙二醛为代表的脂肪氧化次级产物在适宜浓度范围内引起的肌原纤维蛋白氧化较为温和,丙二醛浓度为0.25 mmol/L时肌原纤维蛋白发生的轻度氧化能够促进蛋白质结构伸展,暴露更多活性位点,有助于蛋白质之间的交联,可能对鱼糜凝胶的形成有促进作用。

The impact of secondary products from lipid oxidation on structure and functional characteristics of silver carp myofibrillar protein were studied by using malondialdehyde(MDA)oxidizing systems(0–1.00 mmol/L).The results showed that the contents of carbonyl and free amino groups content changed slightly with increasing MDA concentration from 0.05 to 0.50 mmol/L.The active thiol contents and surface hydrophobicity were enhanced as the malondiadehyde concentration was increased to 0.25 mmol/L,but dityrosine content decreased somewhat;Ca^2+-ATPase activity initially decreased and then increased,whereas the opposite trend was observed for its solubility.Sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE)indicated that oxidation promoted the crosslinking and aggregation of myofibrillar protein molecules mainly through disulfide bonds.The increasing MDA concentration resulted in a reduction inα-helix content and an increase inβ-sheet content.The results implicate that in the proper concentration range,MDA as a representative of the secondary products of lipid oxidation led to mild oxidation of myofibrillar protein,and the mild oxidation of myofibrillar protein at MDA concentration of 0.25 mmol/L promoted partial unfolding of myofibrillar protein,resulting in exposure of more active sites and consequently protein cross-linking,which might contribute to the formation of surimi gel.