酶、多肽电荷数的理论计算及误差研究

对酶的电荷数随ｐＨ变化的定量关系进行了理论推导，将推导出的酶的电荷数与ｐＨ的关系式应用于多肽等电点的计算，理论计算结果与文献实验结果完全一致，并推导出酸性氨基酸、碱性氨基酸及中性氨基酸等电点的计算式，与现有计算式完全一致．应用荧光光谱和荧光偏振对肌酸激酶带电性随ｐＨ值的变化关系的研究表明，理论计算符合实验结果，表明：此文理论关系式是可靠的．

Calculation and Error of the Number of Charges of Enzyme and Polypeptide

The relations between the number of charges of enzyme and pH have been derived theoreticaly,the number ( X ) of negative charges was calculated with the formula, X =∑4 i=0 K a i · n i + K a i ,and the number ( Y ) of positive charges with another formula, Y =∑3 i=0 m i + K bi ,and the number ( H )of net charges with the formula, H=Y-X =∑3 i=0 m i + K bi -∑4 i=0 K a i ·n i + K a i .The number of charges of three enzymes was calculated from pH2 to pH14,there are two points at which the number of charges of enzyme varied greatly,they were pH4 and pH11.The p I of enzyme and polypeptide can be calculated with the formula,∑4 i=0 K ai n i + K ai =∑3 i=0 m i + K bi ,the p I of some polypeptide were calculated, and the values of calculation were the same as those from the references,and the p I formula of amined acid was derived from the p I formula of enzyme,and they were the same as the formula that has been used now.The relation between the number of charges of creatine kinase and pH was studied with fluorescence polarization and fluorescence spectrum,and the wave length of maxium fluorescent emission and degree of polarization varied greatly at pH4 and pH11,which fited for the number of charges,The results showed that the theoretical results were the same as those of the experiment.The calculative error of the number of charges was discussed too,except for pH10,the error was small,the error at pH10 was primarily caused by Lys,because its p K b distributed from 9 4 to 10 6.These conclusions are reliable.