The LmbB1 protein, participating in the biosynthesis of lincomycin,was heterologously expressed inEscherichia coli, purified in its active form, and characterized as a dimer of identical subunits. Methods for purification and analysis of the LmbB1 reaction product were developed. Molecular mass and fragmentation pattern of the product revealed by capillary electrophoresis-mass spectrometry were in agree-ment with its proposed structure, 4-(3-carboxy-3-oxo-propenyl)-2,3-dihydro-1H-pyrrole-2-carboxylic acid. The LmbB1 is therefore a dioxygenase catalysing the 2,3-extra-diol cleavage of theL-3,4-dihydroxyphenyl alanine aromatic ring
