Characterization of Bphl, an aldolase involved in the degradation pathway of polycholorinated biphenyls
A complex of an aldolase and a dehydrogenase involved in ' bph' degradation pathway of polychlorinated biphenyls in ' Burkholderia xenovorans' LB400 was purified. The aldolase, BphI, has the highest activity with Mn2+ cofactor and was able to convert 4-hydroxy-2-oxoacids of 5 to 7 carbon atoms to pyruvate and the corresponding aldehyde. The enzyme was competitively inhibited by the pyruvate enolate analogue, oxalate, with 'K'ic of 0.93 [mu]M. It is able to catalyze the proton exchange of pyruvate with an activity of 0.26 [mu]mol·min· -1·mg-1. A catalytic base with a p'K 'a of 7.7 is involved in the reaction. BphI R16A mutant was inactive while R16K mutant has a 1400-fold lower catalytic efficiency ('k'cat/'K'm). The Y290F mutant has a 30-fold lower 'k'cat suggesting that Tyr-290 might not serve as a proton donor. BphI activity was activated 3-fold by the BphJ cofactor, NADH, indicating the existence of allosteric regulation of BphI activity by BphJ.