Phosphoribosyl-anthranilate isomerase: indole—3-glycerol-phosphate-synthase, a monomeric bifunctional enzyme of M r = 49 500 from Escherichia coli, catalyses 2 sequential reactions in the synthesis of tryptophan from chorismate. Its amino acid sequence, as predicted from the gene sequence, comprises 452 amino acids. Crystals in space group P41 (or P43) have been grown from ammonium sulphate, and in P41212 (or P43212) from polyethyleneglycol, by vapour diffusion and seeding techniques. Three heavy-atom derivatives of the P41 form with cell dimensions a = 104.7 Å and c = 67.7 Å have been prepared. A structure determination is underway.
