On the evolution of an oligocephalic enzyme. glutamine-chorismate-amidotransferase-free anthranilate phosphoribosyltransferases from mutant strains of Salmonella typhimurium.

(1) A procedure has been described for the purification of two glutamine-chorismate-amidotransferase-free anthranilate phosphoribosyltransferases from mutant strains TAX6trpR782 and trpAB1653trpR782 of Salmonella typhimurium. (2) The native enzymes tend to aggregate forming polymers of molecular weights 333,000 in the case of TAXtrpR782 and 220,000 and larger than 1X10(6) in the case of trpAB1653trpR782. In the presence of sodium dodecyl sulfate the polymer of trpAB1653trpR782 dissociates into a single component with molecular weight of 72,000. (3) In contrast to anthranilate phosphoribosyltransferase of the wild type component II, the glutamine-chorismate-amidotransferase-free proteins do not complex with component I. They do however show catalytical similarities with the wild type with respect to anthranilate phosphoribosyltransferase activity.