Kumar A A, Blankenship D T, Kaufman B T, Freisheim J H
Biochemistry. 1980 Feb 19;19(4):667-78. doi: 10.1021/bi00545a010.
The complete covalent structure of dihydrofolate reductase from chicken liver is described. The S-carboxymethylated protein was subjected to cleavage by cyanogen bromide which produced five fragments. Fragment CB2 contained an internal homoserine residue which was not cleaved by cyanogen bromide. Sequences and ordering of the cyanogen bromide fragments were established by means of automated sequencer analyses of the fragments and from smaller peptides generated by proteolysis with trypsin and staphylococcal protease. The covalent structure of the single polypeptide chain comprises 189 residues of molecular weight 21,651. The chicken liver enzyme is homologous to that from L1210 cells and shows regions of homology to dihydrofolate reductases from Streptococcus faecium, Escherichia coli, and Lactobacillus casei. These homologous regions in the chicken liver enzyme are primarily related to conserved amino acid residues implicated in the binding of NADPH and methotrexate by bacterial dihydrofolate reductases.
本文描述了鸡肝二氢叶酸还原酶的完整共价结构。对S-羧甲基化蛋白进行溴化氰裂解，产生了五个片段。片段CB2含有一个内部高丝氨酸残基，该残基未被溴化氰裂解。通过对片段以及用胰蛋白酶和葡萄球菌蛋白酶进行蛋白水解产生的较小肽段进行自动测序分析，确定了溴化氰片段的序列和顺序。单条多肽链的共价结构由189个残基组成，分子量为21,651。鸡肝酶与L1210细胞中的酶同源，并显示出与粪肠球菌、大肠杆菌和干酪乳杆菌的二氢叶酸还原酶的同源区域。鸡肝酶中的这些同源区域主要与细菌二氢叶酸还原酶中参与NADPH和甲氨蝶呤结合的保守氨基酸残基有关。
