Occurrence and properties of glutathione S-transferases in phenol-degrading Pseudomonas strains

Pseudomonas sp. strains, able to degrade aromatic compounds such as phenol, were chosen to investigate the occurrence and characteristics of glutathione S-transferases (GSTs). Affinity chromatography purification showed the presence of at least one GST in each studied strain. The purified proteins exhibited a great variety in the N-terminal sequences and different enzyme activities with the standard GST substrates tested. Two Pseudomonas strains, M1 and CF600, were chosen to investigate the GST activities under different growth conditions. Therefore, cells were grown either on phenol or on different nonaromatic carbon sources in the presence and absence of increasing phenol concentrations. In strain M1 a strong correlation between the activities of the catechol 1,2-dioxygenase and GST was observed in all the tested conditions. Moreover, growth on different organic acids also affected GST activity levels, with a negative correlation with the specific growth rate determined by each substrate. These results suggest a possible function of GST as a response to specific metabolic conditions determined by phenol toxicity and/or catabolism and the metabolic status of the cells. The same experiments performed with the CF600 strain did not show induction of GST activity in any of the tested conditions, indicating that GST_CF600 probably has a different role in cell metabolism. Native gel electrophoresis gave indications that GST dimerization could be an important process in the modulation of GST activity.