Purification and Comparison of the N‐(5′‐Phosphoribosyl)anthranilic Acid Isomerase/Indole‐3‐glycerol Phosphate Synthetase of Tryptophan Biosynthesis from Three Species of Enterobacteriaceae

Abstract

A measure of evolutionary divergence between three species of the enterobacteriaceae was made by studying the physical properties of a protein common to all three, N‐(5′‐phosphoribosyl)‐anthranilic acid isomerase indole‐3‐glycerol phosphate synthetase, a bifunctional enzyme of the tryptophan biosynthetic pathway. The protein was purified to near homogeneity from Aerobacter aerogenes, Escherichia coli, and Salmonella typhimurium. The purified proteins were found to be very similar in their ultraviolet absorption spectra, fluorescence emission and excitation spectra, and molecular weights. Various determinations of the molecular weights varied from 4.4 to 5.1 × 104 daltons, and no significant differences were observed between the purified proteins and the enzymes in crude extracts. The electrophoretic behaviour of each of the three purified proteins on polyacrylamide gels with sodium dodecyl sulphate were similar and consistent with each enzyme consisting of a single polypeptide chain. Peptide patterns of each of the proteins were obtained following digestion with trypsin plus chymotrypsin. Close homology in primary structure between the proteins was suggested by the observation that approximately half the peptides of any two proteins were identical. Comparison with similar data from a previous study on the α subunit of tryptophan synthetase suggests that there has been no great difference in the rate of divergence of the α subunit and phosphoribosylanthranilate isomerase‐indole‐glycerol‐phosphate synthetase in the species studied. Copyright © 1970, Wiley Blackwell. All rights reserved