Subcellular/tissue distribution and responses to oil exposure of the cytochrome P450-dependent monooxygenase system and glutathione S-transferase in freshwater prawns (Macrobrachium malcolmsonii, M. lamarrei lamarrei).

Subcellular fractions (mitochondrial, cytosolic and microsomal) prepared from the tissues (hepatopancreas, muscle and gill) of freshwater prawns Macrobrachium malcolmsonii and Macrobrachium lamarrei lamarrei were scrutinized to investigate the presence of mixed function oxygenase (MFO) and conjugating enzymes (glutathione-S-transferase, GST). Cytochrome P450 (CYP) and other components (cytochrome b(5); NADPH-cytochrome c (CYP) reductase and NADH-cytochrome c-reductase activities) of the MFO system were predominantly present in the hepatic microsomal fraction of M. malcolmsonii and M. lamarrei lamarrei. The results are in agreement with the notion that monooxygenase system is mainly membrane bound in the endoplasmic reticulum, and that the hepatopancreas is the major metabolic tissue for production of biotransformation enzymes in crustaceans. Further, the prawns were exposed to two sublethal (0.9 ppt (parts per thousand) and 2.3 ppt) concentrations of oil effluent. At the end of 30th day, hydrocarbons and detoxifying enzymes were analysed in the hepatopancreas. The accumulations of hydrocarbon in the tissues gradually increased when exposed to sublethal concentrations of oil effluent and were associated with significantly enhanced levels of cytochrome P450 (180.6+/-6.34 pmol mg(-1) protein (P<0.05 versus control, 136.5+/-7.1 pmol mg(-1) protein) for 2.3 ppt and 305.6+/-8.5 pmol mg(-1) protein (P<0.001 versus control, 132.3+/-6.8 pmol mg(-1) protein] for 0.9 ppt of oil exposed M. malcolmsonii; 150+/-6.5 pmol mg(-1 )protein (P<0.01 versus control, 84.6+/-5.2 pmol mg(-1) protein) for 2.3 ppt and 175+/-5.5 pmol mg(-1) protein (P<0.01 versus control, 87.6+/-5.4 pmol mg(-1) protein) for 0.9 ppt of oil exposed M. lamarrei lamarrei), NADPH cytochrome c-reductase activity (14.7+/-0.6 nmol min(-1 )mg(-1) protein (P<0.05 versus control, 6.8+/-0.55 nmol min(-1 )mg(-1) protein) for 2.3 ppt and 12.1+/-0.45 nmol min(-1 )mg(-1) protein (P<0.01 versus control, 6.9+/-0.42 nmol min(-1 )mg(-1) protein) for 0.9 ppt of oil exposed M. malcolmsonii; 12.5+/-0.31 nmol min(-1 )mg(-1) protein (P<0.001 versus control, 4.6+/-0.45 nmol min(-1 )mg(-1) protein) for 2.3 ppt and 9.6+/-0.32 nmol min(-1 )mg(-1) protein (P<0.01 versus control, 4.9+/-0.41 nmol min(-1 )mg(-1) protein) for 0.9 ppt of oil exposed M. lamarrei lamarrei) and cytochrome b(5 )(124.8+/-3.73 pmol mg(-1) protein (P<0.01 versus control, 76.8+/-4.2 pmol mg(-1) protein) for 2.3 ppt and 115.3+/-3.86 pmol mg(-1) protein (P<0.01 versus control, 76.4+/-4.25 pmol mg(-1 )protein) for 0.9 ppt of oil exposed M. malcolmsonii and 110+/-3.11 pmol mg(-1) protein (P<0.01 versus control, 63.7+/-3.24 pmol mg(-1 )protein) for 2.3 ppt and 95.3+/-2.63 pmol mg(-1) protein (P<0.01 versus control, 61.4+/-2.82 pmol mg(-1) protein) for 0.9 ppt of oil exposed M. lamarrei lamarrei). The enhanced levels of biotransformation enzymes in oil-exposed prawns demonstrate a well-established detoxifying mechanism in crustaceans, and the response offers the possibility of use as a biomarker for the early detection of oil pollution.