title: Denitrification, a novel type of respiratory metabolism in fungal mitochondrion.
abstract: Subcellular localization and coupling to ATP synthesis were investigated with respect to the denitrifying systems of two fungi, Fusarium oxysporum and Cylindrocarpon tonkinense. Dissimilatory nitrate reductase of F. oxysporum or nitrite reductase of C. tonkinense could be detected in the mitochondrial fraction prepared from denitrifying cells of each fungus. Fluorescence immunolocalization, cofractionation with mitochondrial marker enzymes, and cytochromes provided evidence that the denitrifying enzymes are co-purified with mitochondria. Respiratory substrates such as malate plus pyruvate, succinate, and formate were effective donors of electrons to these activities in the mitochondrial fractions. Moreover, nitrite and nitrate reduction were shown to be coupled to the synthesis of ATP with energy yields (P:NO3- or P:2e ratios) of 0.88 to 1.4, depending upon whether malate/pyruvate or succinate were provided as substrates. Nitrate or nitrite reductase activity was inhibited by inhibitors such as rotenone, antimycin A, and thenoyltrifluoroacetone. Thus, fungal denitrification activities are localized to mitochondria and are coupled to the synthesis of ATP. The existence of these novel respiration systems are discussed with regard to the origin and evolution of mitochondria.
authors.affiliation: Institutes of Applied Biochemistry and Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuo
authors.forename: A
authors.initials: A
authors.lastname: Takimoto
authors.forename: S
authors.initials: S
authors.lastname: Suzuki
authors.forename: F
authors.initials: F
authors.lastname: Maruo
authors.forename: H
authors.initials: H
authors.lastname: Shoun
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000255:Adenosine Triphosphate / Q000378:metabolism; D000968:Antimycin A / Q000494:pharmacology; D003580:Cytochromes / Q000378:metabolism; D004734:Energy Metabolism; D005670:Fusarium / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D003904:Mitosporic Fungi / Q000378:metabolism*; D009565:Nitrate Reductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009572:Nitrite Reductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D011506:Proteins / Q000302:isolation & purification / Q000378:metabolism*; D012402:Rotenone / Q000494:pharmacology; D055765:Shc Signaling Adaptor Proteins; D013053:Spectrophotometry; D013804:Thenoyltrifluoroacetone / Q000494:pharmacology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D003580:Cytochromes; D020662:Guanine Nucleotide Exchange Factors; D011506:Proteins; D055765:Shc Signaling Adaptor Proteins; D012402:Rotenone; D013804:Thenoyltrifluoroacetone; D000968:Antimycin A; D000255:Adenosine Triphosphate; D009565:Nitrate Reductases; D009572:Nitrite Reductases