THE GENES LMBB1 AND LMBB2 OF STREPTOMYCES-LINCOLNENSIS ENCODE ENZYMESINVOLVED IN THE CONVERSION OF L-TYROSINE TO PROPYLPROLINE DURING THE BIOSYNTHESIS OF THE ANTIBIOTIC LINCOMYCIN-A

The genes lmbA,B1,B2 in the Lincomycin A production gene cluster of St reptomyces lincolnensis were shown to form a common transcription unit with the promoter located directly upstream of lmbA. The proteins Lmb B 1 (mol. mass, 18 kDa) and LmbB2 (mol. mass 34 kDa), when over-produc ed together in Escherichia coli, brought about enzyme activities for t he specific conversion of both L-tyrosine and L-3,4-dihydroxyphenylala nine (L-DOPA) to a yellow-colored product. The LmbB1 protein alone cat alyzed the conversion of L-DOPA, but not of L-tyrosine. The purified L mbB1 protein showed a K-m for L-DOPA of 258.3 mu M. The L-tyrosine con verting activity could not been demonstrated in vitro. The preliminary interpretation of these data suggests that the protein LmbB 1 is an L -DOPA extradiol-cleaving 2,3-dioxygenase and that the protein LmbB2, e ither alone or in accord with LmbB 1, represents an L-tyrosine 3-hydro xylase. This sequence of putative oxidation reactions on L-tyrosine se ems to represent a new pathway different from the ones catalyzed by ma mmalian L-tyrosine hydroxylases or the wide-spread tyrosinases. The pr otein LmbA seemed not to be involved in this process. The labile, yell ow-colored product from L-DOPA could not be converted to a picolinic a cid derivative [3-(2-carboxy-5-pyridyl) alanine] in the presence of am monia. Therefore, it probably is not a derivative of a cis,cis-3-hydro xymuconic acid semialdehyde; instead, its speculative structure repres ents a heterocyclic precursor of the propylhygric acid moiety of linco mycin A.