The Effects Of PH On The Activity Of ICL From Several Sources

Extracting isocitrate lyase from three kinds of bacteria and four kinds of plants to explore the activity of the enzyme in different pH and analyse the correlation between pH and amino acid sequence.The same buffer and method were used to detect the activity of the enzyme.The result shows that the optimal PH of the isocitrate lyase in Escherichia coli,Mycobacterium tuberculosis and Pseudomonas aeruginosa are 5.6,6 and 7 respectively,and the optimal pH-value of ICL are 6?6.6?6.6?7.6 in Zea mays,Glycine max,Cucumis sativus and Solanum tuberosum.According to the amino acid sequence of ICL,it is clear that there was no direct correlation between the optimal pH of the enzyme and the number or percentage of a kind of amino acid(including positive and negative charged amino acid in neutral conditions,aromatic amino acids,polar and nonpolar amino acid).However,it was founded that the percentage of histidine of the ICL in the 7 species are 1.83%,2.33%,2.63%.2.09%,2.49%,2.42%,2.60%,and the content of histidine residues were almost same in both soybean and cucumber,in which the optimum pH of the enzyme were 6.6.The research shows that the optimal pH of isocitrate lyase in 7 species has relationship with the content of histidine residues.As the content of histidine residues rose,the optimal pH of isocitrate lyase increased.