OVERLAPPING SUBSTRATE SPECIFICITIES OF BENZALDEHYDE DEHYDROGENASE (THE XYLC GENE-PRODUCT) AND 2-HYDROXYMUCONIC SEMIALDEHYDE DEHYDROGENASE (THE XYLG GENE-PRODUCT) ENCODED BY TOL PLASMID PWWO OF PSEUDOMONAS-PUTIDA

Two aldehyde dehydrogenases involved in the degradation of toluene and xylenes, namely, benzaldehyde dehydrogenase and 2-hydroxymuconic semi aldehyde dehydrogenase, are encoded by the xylC and xylG genes, respec tively, on TOL plasmid pWW0 of Pseudomonas putida, The nucleotide sequ ence of xylC was determined in this study, A protein exhibiting benzal dehyde dehydrogenase activity had been purified from cells of P. putid a(pWW0) (J. P. Shaw and S. Harayama, fur. J. Biochem, 191:705-714, 199 0); however, the aminoterminal sequence of this protein does not corre spond to that predicted from the xylC sequence but does correspond to that predicted from the xylG sequence. The protein purified in the ear lier work was therefore 2-hydroxymuconic semialdehyde dehydrogenase (t he xylG gene product). This conclusion was confirmed by the fact that this protein oxidized 2-hydroxymuconic semialdehyde (k(cat)/K-m = 1.6 x 10(6) s(-1) M(-1)) more efficiently than benzaldehyde (k(cat)/K-m = 3.2 x 10(4) s(-1) M(-1)). The xylC product, the genuine benzaldehyde d ehydrogenase, was purified from extracts of P. putida(pWW0-161 Delta x ylG) which does not synthesize 2-hydroxymuconic semialdehyde dehydroge nase. The amino-terminal sequence of the purified protein corresponds to the aminoterminal sequence deduced from the xylC sequence, This enz yme efficiently oxidized benzaldehyde (k(cat)/K-m = 1.7 x 10(7) s(-1) M(-1)) and its analogs but did not oxidize 2-hydroxymuconic semialdehy de or its analogs.