Random replacement of phenylalanine by p-Fluorophenylalanine in alkaline phosphatase(s) formed during biosynthesis by E. coli

Tryptic digests of phenylalanine-labelled alkaline phosphatase from Escherichia coli contain six phenylalanine peptides, four having one phenylalanine residue per molecule and two having two phenylalanines per molecule. Examination of enzyme labelled with [ 14C] p-fluorophenylalanine showed that all the phenylalanine peptides have their p-nuorophenylalanine counterparts and therefore all the phenylalanine residues in alkaline phosphatase are accessible to replacement by the p-fluoro derivative. Experiments to measure the degree of replacement of phenylalanine by p-fluorophenylalanine at each site under conditions of direct competition between the amino acids show no evidence of variable discrimination between the amino acids from site to site.