Camp. Eiochem. Physiol. Vol. 104C, No. I, pp. 137-145, 1993 Printed in Great Britain 03064492/93 $6.00 + 0.00 0 1993 Pergamon Press Lid DRUG AND XENOBIOTIC METABOLISING ENZYMES IN CAMEL LIVER: MULTIPLE FORMS AND SPECIES SPECIFIC EXPRESSION H. RAZA and W. MONTAGUE Department of Biochemistry, Faculty of Medicine and Health Sciences, U.A.E. University, P.O. Box 17666, Al Ain, United Arab Emirates (Fax 638-247) (Received 22 June 1992; accepted for publication 3 1 July 1992) zyxwvutsrqponmlkjihgfedcbaZYX Abstract-I. Previous studies have demonstrated the presence of phase I mixed-function oxidases (cytochrome P,,,-dependent) and phase II conjugation (glutathione S-transferase) enzymes in camel liver. This study represents further characterisation of these drug metabolising enzyme systems in camel liver by comparing their catalytic and immunochemical properties with enzymes of rat and mouse liver. 2. Usmg the specific PdsO substrate aniline, the microsomal aniline hydroxylase activity of camel liver was found to be significantly lower than that of rat and mouse. The K,,, values of the enzyme for aniline was similar in rat and camel liver; however, the V,,,,, for camel liver enzyme was 50% of the rat liver enzyme. Aminopyrene N-demethylase activity in camel liver, was lower than that of rat but higher than in mouse. Microsomal NADPH cytochrome C-reductase and NADPH-supported lipid peroxidation activities were similar in all three species. 3. The cytosolic phase II conjugation enzyme glutathione S-transferase and glutathione peroxidase activities in camel liver were markedly lower than those of rat and mouse enzymes. However, GSH concentration was similar in all three species. 4. Immunodot blot and Western blot analysis of liver cytosols, using antibodies to specific GST isoenzymes, have shown that camel liver like mouse and rat, expresses predominantly the Alpha and Mu classes of GST. GST Pi on the other hand, was abundant in mouse liver and was underexpressed in camel and rat liver. 5. Our results demonstrate that there are multiple forms of phase I (P,& and phase II (GST) enzymes in camel liver and that they are comparable with the drug metabolising enzymes of rat and mouse. The lower a&ties of drug metabolising enzymes in camel liver compared with rat and mouse appear to be related to the differential expression of selective Pd5,, and GST isoenzymes. INTRODUCllON Hepatic cytochrome Pd5,, (PdsO) and glutathione S-transferase (GST) are the most active drug metabolising enzymes that participate in the metab- olism of a wide variety of exogenous and endogenous compounds in mammals (Jakoby, 1977; Gonzalez, 1989; Guengerich, 1991). These compounds include drugs, chemical carcinogens, pollutants, fatty acids, steroids, vitamins, prostaglandins and leukotrienes (Chasseaud, 1979; Guengerich et al., 1982; Nebert and Gonzalez, 1987; Chang et al., 1987). Many isoenzymes of Pbso have been purified from mam- malian tissues and characterized on the basis of their catalytic and molecular properties (Guengerich et al., 1982; Nebert and Gonzalez, 1987; Raza and Avadhani, 1988; Gonzalez, 1989; Raza et al., 1992a). Similarly several GST isoenzymes have been ident- ified in mammalian tissues (Mannervik et al., 1985; Hayes and Mantle, 1986; Raza et al., 1991). Man- List of abbreviations: GSH, reduced glutathione; Pd5,,, cyto- chrome Peso, GST, glutathione S-transferase; GSH-Px, glutathione peroxidase; CDNB, I-chloro2-4-dinitroben- zene; NADPH, reduced nicotinamide adenine dinucle- otide phosphate; SDS-PAGE, sodium dodecyl sulphate polyacrylamide gel electrophoresis. nervik et al. (1985) have characterised mammalian GST isoenzymes and classified them into three dis- tinct classes: Alpha (basic), Mu (neutral) and Pi (acidic). All three isoenzymes are immunochemically distinguishable and exhibit substrate specificity (Mannervik et al., 1985 and Raza et al., 1991). The major role of drug metabolising enzymes is to convert lipid-soluble compounds into water-soluble metabolites with diminished biological activity. How- ever, in some instances, these enzymatic changes may generate chemically reactive metabolites which can activate physiological or pathological processes (Conney, 1982; Guengerich, 1991). The balance of metabolic activation and inactivation of drugs and other xenobiotics in particular tissues is an important factor in organ-specific toxicity. Although PdsOis normally considered as an activation enzyme, and GST as a detoxification enzyme (Gibson and Skett, 1986), the relative expression of the various isoen- zymes of P,,, and GST is critical in determining the balance between toxication and detoxication path- ways. The GST isoenzymes conjugate reactive elec- trophilic compounds with cellular nucleophilic gluta- thione (GSH) and play an important role in promoting cellular resistance to chemotherapeutic 137