Mechanisms of desmutagenic effect by pheophytin
2002
Yoshikawa, K. (Kinki Univ., Higashiosaka, Osaka (Japan). Faculty of Agriculture) | Shimizu, K. | Sakai, T. | Terashita, T.
In order to elucidate the desmutagenic mechanisms of mutation suppression by pheophytin b the effect of pheophytin b on oxygenase activity, particularly the aryl hydrocarbon hydroxylase (AHH), and the O-ethoxyresorufin deethylase (OERD) activities of S9 were investigated. The inhibition of AHH activity at higher concentrations of pheophytin clearly indicates that pheophytin b inhibits the monooxygenase activity associated with cytochrome P-450 in S9. The inhibition of OERD activity clearly indicate that pheophytin b inhibits the oxygenase activity of cytochrome P-450 1 A2 of microsomal protein. A study performed to elucidate the desmutagenic mechanisms of action showed that pheophytin b inhibited the reduction of cytochrome C by the NADPH-Cytochrome C reductase of S9. The inhibition was dose dependent until the optimum inhibition was attained, and further increase in the concentration of pheophytin b did not increase the inhibition. In conclusion, pheophytin b inhibits the cytochrome P-450 1A2-mediated hydroxylation of an indirect mutagen such as heterocyclic amine by competitive inhibition of the reduction of cytochrome P-450 1A2 in S9.
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