Dihydrofolate reductase: the amino acid sequence of the enzyme from a methotrexate-resistant mutant of Escherichia coli

Abstract
The determination of the amino acid sequence of the enzyme dihydrofolate reductase (5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3) from a mutant of E. coli B is described. The 159 residues were positioned by automatic Edman degradation of the whole protein, of the reduced and alkylated CNBr fragments, and of selected tryptic, chymotryptic and thermolytic digestion products. An N-bromosuccinimide produced fragment of the largest CNBr peptide was also used in the sequence determination.