Studies on Cytochrome P-450 of the fungus, Fusarium oxysporum

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(1) A semianaerobic culture of the cytochrome P-450(P-450)-producing fungus, Fusarium oxsporum, was shown to evolve nitrogen gas(N_2) then nitrite(or nitrate) was present in the culture medium. This process(denitrification) is now under investigation whether it is due to biological or non-biological reactions.(2) In addition to P-450 cytochrome b_5 was isolated from F. oxysporum. It was shown that the fungus possesses an electron transport system similar to those in hepatic microsomes.(3) The mechanism of induction of P-450 by nitrate(nitrite) was further studied. Addition of nitrate by the concentration as low as below l mM was sufficiently effective in inducing P-450 in the fungus. Other nitrogen sources such as ammonium or amino acids or sulfate were not effective. P-450 was induced on 1-2 days after addition of nitrate. The induction was not repressed by ammonium or other reduced nitrogen souces showing that the P-450 is not involved in the assimilatory metabolism of nitrate. On the other hand, the induction was inhibited by cycloheximide.(4) Distribution of the nitrate-inducible P-450 among eukaryotic microorganisms was investigated. It was shown to be restricted to several species of Fusarium and Gibberella Fujikuroi. The cell-free extracts of these fungi contained intrate-inducible P-450 as well as substances that cross-react with the antibody against purified nitrate-inducible P-450.