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

(1)产细胞色素P-450(P-450)的枯萎病菌在半厌氧培养过程中会放出氮气(N_2)，继而产生亚硝酸盐(或硝酸盐)。这一过程(反硝化)是由生物反应还是非生物反应引起的，目前正在研究中。(2)除P-450外，还从尖孢镰刀菌中分离到细胞色素b_5。进一步研究了硝酸盐(亚硝酸盐)诱导P-450蛋白表达的机制。添加浓度低于L mM的硝酸盐对该真菌P-450的诱导效果较好。其他氮源，如铵、氨基酸或硫酸盐则无效。P-450在加入硝酸盐后1-2天被诱导。这种诱导不受铵或其他还原氮源的抑制，表明P-450不参与硝酸盐的同化代谢。另一方面，环己酰亚胺抑制了这种诱导。(4)研究了硝酸盐诱导的P-450在真核微生物中的分布。结果表明，该菌仅限于几种镰刀菌和赤霉菌。这些真菌的无细胞提取物含有内源性诱导的P-450，以及与纯化的硝酸盐诱导的P-450抗体发生交叉反应的物质。

(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.