Amino Acid Sequence of Escherichia coli Alkaline Phosphatase. Amino- and Carboxyl-Terminal Sequences and Variations between Two Isozymes

The amino- and carboxyl-terminal fragments of E. coli alkaline phosphatase, produced by cyanogen bromide cleavage, have been isolated. The carboxyl-terminal fragment, CB-VI, contains seven amino acid residues in the sequence Lys-Ala-Ala-Leu-Gly-Leu-Lys. The absence of homo-serine and the coincidence of carboxyl-terminal lysine in native alkaline phosphatase suggest the carboxyl-terminal assignment. The amino-terminal fragment, CB-VII, contains five and four residues when isolated from isozymes 1 and 3, respectively. CB-VII from isozyme 1 possesses the sequence Arg-Thr-Pro-Glu-HSe. The corresponding peptide from isozyme 3 is devoid of the argininyl residue. Amino-terminal analyses of native alkaline phosphatase suggest the amino-terminal alignment of CB-VII. Analyses for carbohydrate indicate both isozymes are devoid of those sugars commonly found in glycoproteins.