Evidence that the pyrromethane cofactor of hydroxymethylbilane synthase (porphobilinogen deaminase) is bound to the protein through the sulphur atom of cysteine-242

Abstract
The pyrromethane cofactor of hydroxymethylbilane synthase (porphobilinogen deaminase) from Escherichia coli is bound to the protein through the sulphur atom of a cysteine residue [Hart, Miller & Battersby (1988) Biochem. J. 252, 909-912; Beifuss, Hart, Miller & Battersby (1988) Tetrahedron Lett. 29, 2591-2594]. We show that the pyrromethane-binding residue is cysteine-242.