THE JOURNALS OF BIOLOGICAL C~remsm~

A total of three pyridoxyl-peptides were isolated from the inducible argmine decarboxylase of Escherichia coli B following reduction with NaBH4 and proteolysis with trypsin or chymotrypsin. Sodium borohydride reduces the Schiff base formed between pyridoxal-5’-P and the e-amino group of a lysyl residue of the protein. The sequence analysis of the three peptides is consistent with a unique pyridoxal-P binding site which has the structure Ala-Thr-His-Ser-Thr-His(P-Pxy)Lys-Leu-Leu-Asn-Ala-Leu-Ser-Gln-Ala-Ser-Tyr. This sequence has several residues (including a histidyl residue adjacent to P-pyridoxyl lysine) which are identical with or very similar to the corresponding residues of glutamate decarboxylase from E. coli W; their possible participation in catalysis is discussed. Data are presented which demonstrate the power of a “differential” technique for the isolation of pyridoxyl-peptides; this approach, similar to the “diagonal” procedure of Brown and Hartley (Biochem. J., 89, 59P (1963)) is based on the altered elution of these peptides from ion exchange resins after treatment with alkaline phosphatase.