Enzyme systems, trout

This epoxidation of AFB has been associated with aldrin epoxidase (AE) activity in trout (30). As with other epoxide carcinogens, OAFB may be a substrate 7or epoxide metabolizing enzyme systems such as epoxide hydrase (EH) (EC4.2.1.63) and glutathione-S-epoxide transferase (GTr) (EC4.4.1.7) found in mammals and fish (31, 32, 33, 34). AFB also undergoes a variety of other reactions, generally to less toxic metabolites depending on the species of animal involved (35, 36). The primary AFB metabolite in rainbow trout has been shown to be a reduced form of AFB, aflatoxicol (AFL) (24). 

The present study was undertaken to determine the influence of several levels of dietary casein upon the activities of trout hepatic enzyme systems which may be involved in the in vitro activation and detoxification of AFB. In addition, the effect of Technical Paper No. 4883, Oregon Agricultural Experiment Station. 

The decrease in cytochrome P-450 content correlated with a lowering of trout AE activity observed in hepatic microsomes recovered from fish fed high levels of casein, versus those from fish fed low casein diets. As shown in Table III, up to a 32% decrease in the production of the epoxide dieldrin was noted. Similar results have been observed in 10 month old rainbow trout with a nearly identical maximum decrease (unpublished data). Since AFB activation has been shown to involve a cytochrome P-450 dependent enzyme system (19, 20, 22) and trout... 

The observed mutagenic responses to AFB reflect the overall effects of activation and detoxification systems on the in vitro metabolism of AFB. It appeared that the effect of high casein levels fed to trout was that a greater amount of activated AFB was produced and/or that less could be detoxified by these fish than by those fed lower casein diets. If lowered cytochrome P-450 content and AE activities in fish fed the high casein diets represented a decrease in the activation of AFB, then these effects were overcome by the observed decreases in GTr activity and/or increases in AFB conversion to AFL relative to those of trout fed lower casein diets. Alternately, the results could be explained by dietary effects upon some unknown OAFB metabolizing enzyme system in trout, upon free GSH levels in hepatic tissue, or that the levels of the cytochrome P-450 involved in AFB activation were not reflected by the observed total cytochrome P-450 levels. 

Most fish lack enzyme systems necessary to metabolize PCBs with four or more chlorines per molecule into water-soluble, excretable metabolites. For example, Lieb et al. detected no change in the Aroclor 1254 pattern in Rainbow Trout after 32 weeks on contaminated... 

Stott, W.T. and Sinnhuber, R.O. Trout hepatic enzyme activation of aflatoxin-B] in a mutagen assay system and inhibitory effects of PCBs. Bull. Environ. Contam. Toxicol. (1978) 19, 35. 

The MFO system is also known as the aryl hydrocarbon hydroxylase (AHH) or drug-metabolizing system in mammals. In fish, as in mammals, most MFO activity is localized in the liver (2.404 /imoles of B[a]P hydroxylase = AHH) and in minor amounts in kidney (0.026) and heart (0.006) (Pederson etaL, 1974). Many studies have shown the presence of various oxygenases in fish (Bend etal, 1977 Stegeman, 1978). AHH is present in many marine fish species from different habitats and life stories (Payne, 1977). Several fish species including rainbow trout can hydroxylate benzo[a]pyrene and naphthalene. Quantitative data on AHH activity based on B[a]P hydroxylase activity, benzphetamine demethylase activity, 7-ethoxycoumarin deethylase activity, and cytochrome P-450 content in vertebrates, crustaceans, and bivalves are available in the literature (Vandermeulen and Penrose, 1978 Philpot etaL, 1976). Specific enzyme activities derived from single substrate measurements are limited in their application to complex mixtures of petroleum hydrocarbons (Malins, 1977a, b). MFO absence or activity could determine hydrocarbon retention in... 

The synthesis of protamine in steelhead trout starts from methionine, i.e. methionine acts as chain initiator in protamine synthesis, as it does in protein synthesis in bacterial systems (Wigle and Dixon, 1970). Methionine is incorporated into every component of iridine, constituting some 70% of the total amount of N-terminal amino acids. After tryptic digestion of newly synthesized protamine, a peptide Met-Pro-Arg has been found. The proline residues seems to be the N-terminus of mature protamine. The methionine residue is removed after chain completion by an enzyme found in the extract of testis cells. 

---