Influence of heavy metals on glyceraldehyde-3-phosphate dehydrogenase interactions in Chironomus riparius larvae

Some aquatic organisms can live in contaminated environment due to their adaptable defense mechanism related to their inducible detoxification and excretion. A recent study showed glyceraldehyde-3-phosphate dehydrogenase (GAPDH) can modulate different cellular activities including transcription activation and detoxification. In the present study, the authors report on experiments to test the GAPDH activity of Chironomus riparius toward heavy metals. Glyceraldehyde-3-phosphate dehydrogenase was isolated and purified from C. riparius. The kinetics of the enzyme was measured. The results showed that GAPDH was inhibited by heavy metals including Co(2+) , Cu(2+) , Fe(2+) , Ni(2+) , Pb(2+) , but was activated by zinc ions. The kinetics study of the enzyme showed maximum initial velocity (Vmax) of GAPDH increased by 50%. In addition, the substrate and cofactor affinity increased in the presence of zinc. The GAPDH from C. riparius had maximum activities at pH 8.5 and 37 °C. The protein sequence analysis shows that there are 2 additional cysteine and histidine residues in the conserved region of GAPDH from C. riparius, which is believed to play an important role in the interactions with heavy metals. The results suggest that exposure to zinc could modulate GAPDH, which could be related to response of antioxidant defense to other heavy metals.