THE PRIMARY STRUCTURE OF BRANCHED-CHAIN ALPHA-OXO ACID DEHYDROGENASE FROM BACILLUS-SUBTILIS AND ITS SIMILARITY TO OTHER ALPHA-OXO ACID DEHYDROGENASES

The bfmB mutant of Bacillus subtilis requires branched short-chain car boxylic acids for growth because the organism is known to be defective in branched-chain a-oxo acid dehydrogenase. The DNA in the region of bfmB has now been cloned and sequenced, and the gene has been analyzed . The results show that there are three open reading frames in the are a, each of which is preceded by a putative ribosome binding site, and the last of which is followed by a putative transcription termination site with inverted repeats. The amino acid sequences deduced by analys is of the reading frames are highly similar (with 32-49% identity) to the E1alpha, E1beta and E2 components of pyruvate, 2-oxoglutarate and branched-chain alpha-oxo acid dehydrogenases from different sources. T he thiamin diphosphate binding, putative subunit interaction and phosp horylation sites of the E1alpha of four reported branched-chain alpha- oxo acid dehydrogenases from different sources are very similar to tho se of the first open reading frame (E1alpha) of bfmB. A similar result is also obtained with the lipoyl-binding site (lysine) and its domain of the E2 component of alpha-oxo acid dehydrogenases from different s ources. The present data, along with the reported biochemical data, le ad to the conclusion that bfmB encodes a branched-chain alpha-oxo acid dehydrogenase, which is composed of E1alpha, E1beta and E2 genes. Thi s organization is identical to that of the 2-oxoglutarate dehydrogenas e in B. subtilis.