牛初乳中IgG抗原决定簇以及蛋白质G结合部位热变性的对比

Comparative study on thermoresistance of antigen determinant region and protein G-binding region of Immunoglobulin G in colostrum

对比研究热处理(69～81℃)过程中牛初乳IgG分子抗原决定簇部位及其蛋白质G结合部位的变性动力学。利用单向琼脂扩散法(RID)监测IgG分子的热变性状况,其抗原决定簇部位热变性可用反应级数为1.2的方程较好地描述。结果表明,在69,72,77,81℃条件下IgG变性的D值分别为5000,2000,500,270 s,Z值为9.43℃,变性活化能为270.55 kJ/mol;利用蛋白质G亲和色谱法监测IgG分子上蛋白质G结合部位的热变性状况,在反应级数n=1.2,温度在69,72,77,81℃条件下IgG变性的D值分别为14286,3333,625,313 s,Z值为7.25℃,变性活化能为316.42 kJ/mol。所以IgG分子中抗原决定簇部位较之其蛋白质G结合部位更易于受热变性,较之RID,采用蛋白质G亲合色谱法检测牛初乳制品IgG的结果将偏高。

Thermoresistance of the antigen determinant region and Protein G-binding region of bovine immunoglobulin G （IgG） were studied using Single Radial immunodiffusion （SRID） and Protein G affinity chromatography. The kinetic and thermodynamic parameters for heatinduced denaturation of IgG in colostrum matrix were determined over a temperature range of 69-81 ℃. The denaturation of the two IgG regions was both best described assuming an apparent reaction order of 1.2. D values, the time required to reduce the binding activities of IgG by 90%, were 5000, 2000, 500, 270s for RID and 14286, 3333, 625, 313 s for Protein G affartity chromatography at 69,72,77,81 ℃ respectively. Similarly, Z values, the degrees necessary to reduce the D value in one logarithmic cycle, were estimated to be 9.43℃ for SRID and 7.25℃ for Protein G affinity chromatography. The activation energy values of the denature reactions of the antigen determinant region and Protein G-binding region of bovine immunoglobulin G （IgG） were 270.55 and 316.42 kJ/mol respectively. So the antigen determinant region was more labile than Protein G-binding region of IgG, compared to RID, the quantitative results of IgG content in bovine colostrum containing products would be overestimated.