Multisubstrate kinetics of PAH mixture biodegradation: analysis in the double-logarithmic plot

The proposed method of kinetic analysis of aqueous-phase biodegradation of polycyclic aromatic hydrocarbons (PAH) mixture presupposes representation of kinetic curves for each pair of mixture components, S-x and S-y, in double-logarithmic coordinates (In S-x; In S-y). If PAH mixture conversion corresponds to the multisubstrate model with a common active site, then the graphs in double-logarithmic coordinates are straight lines with the angular coefficients equal to the ratio of respective first-order rate constants k(x)(y) = VyKx/KyVx, where K-x, and K-y are half-saturation constants, V-x and V-y are the maximum conversion rates for substrates S-x and S-y; the graph slope does not depend on any concentrations and remains constant during the change of reaction rates as a result of inhibition, induction/inactivation of enzymes or biomass growth. The formulated method has been used to analyze PAH mixture conversion by the culture of Sphingomonas sp. VKM B-2434. It has been shown that this process does not satisfy the multisubstrate model with a single active site. The results suggest that the strain VKM B-2434 contains at least two dioxygenases of different substrate specificity: one enzyme converts phenanthrene and fluoranthene and the other converts acenaphthene and acenaphthylene. The ratios of first-order rate constants have been obtained for these pairs of substrates.