Bhayana V, Duckworth H W
Biochemistry. 1984 Jun 19;23(13):2900-5. doi: 10.1021/bi00308a008.
Detailed evidence for the amino acid sequence of allosteric citrate synthase from Escherichia coli is presented. The evidence confirms all but 11 of the residues inferred from the sequence of the gene as reported previously [Ner, S. S., Bhayana, V., Bell, A. W., Giles, I. G., Duckworth, H. W., & Bloxham, D. P. (1983) Biochemistry 22, 5243]; no information has been obtained about 10 of these (residues 101-108 and 217-218), and we find aspartic acid rather than asparagine at position 10. Substantial regions of sequence homology are noted between the E. coli enzyme and citrate synthase from pig heart, especially near residues thought to be involved in the active site. Deletions or insertions must be assumed in a number of places in order to maximize homology. Either of two lysines, at positions 355 and 356, could be formally homologous to the trimethyllysine of pig heart enzyme, but neither of these is methylated. It appears that E. coli and pig heart citrate synthases are formed of basically similar subunits but that considerable differences exist, which must explain why the E. coli enzyme is hexameric and allosterically inhibited by NADH, while the pig heart enzyme is dimeric and insensitive to that nucleotide.
本文给出了大肠杆菌别构柠檬酸合酶氨基酸序列的详细证据。该证据证实了除先前报道的基因序列推断的11个残基外的所有残基[Ner, S. S., Bhayana, V., Bell, A. W., Giles, I. G., Duckworth, H. W., & Bloxham, D. P. (1983) Biochemistry 22, 5243]；其中10个残基（101 - 108位和217 - 218位）尚未获得相关信息，并且我们发现第10位是天冬氨酸而非天冬酰胺。注意到大肠杆菌酶与猪心柠檬酸合酶之间存在大量的序列同源区域，尤其是在被认为参与活性位点的残基附近。为了使同源性最大化，必须在多个位置假定存在缺失或插入。355位和356位的两个赖氨酸中的任何一个在形式上都可能与猪心酶的三甲基赖氨酸同源，但这两个都未被甲基化。看来大肠杆菌和猪心柠檬酸合酶由基本相似的亚基组成，但存在相当大的差异，这必然解释了为什么大肠杆菌酶是六聚体且被NADH别构抑制，而猪心酶是二聚体且对该核苷酸不敏感。
