The liver monooxygenase system of Brazilian freshwater fish

Content of cytochromes b(5) and P-450, and activities of NADPH-cytochrome c (P-450) reductase (NCR) and 7-ethoxyresorufin O-deethylase (EROD) were mea sured in liver microsomes prepared from two South American endemic fish, Br ycon cephalus and Colossoma macropomum, from tilapia, Oreochromis niloticus , and from Swiss mice, Mus musculus. which served as a control. Strong hemo globin binding to fish liver microsomal membranes (FLM) altered visible spe ctra of microsomal cytochromes. Consequently, special precautions during FL M preparation, including liver perfusion followed by repeated washing of mi crosomes, were required in the study of microsomal cytochromes from these f ish. FLM from all fish studied here had a significantly lower content of mi crosomal cytochromes but a similar level of NCR and EROD activities compare d to mouse liver microsomes (MLM). Strong response of the monooxygenase sys tem in O. niloticus to water pollution was detected with both specific cyto chrome P-450 content and EROD activity increasing sharply. The optical spec tra of hemoglobin from B. cephalus and C. macropomum were analyzed and some differences in shape and relative extinction were observed compared to kno wn hemoglobins. (C) 2000 Elsevier Science Inc. All lights reserved.