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Generation of Adenosine Triphosphate in Cytochrome-deficient Mutants of Neurospora

Slayman, Carolyn W. and Rees, Douglas C. and Orchard, Pamela P. and Slayman, Clifford L. (1975) Generation of Adenosine Triphosphate in Cytochrome-deficient Mutants of Neurospora. Journal of Biological Chemistry, 250 (2). pp. 396-408. ISSN 0021-9258.

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The fungus Neurospora crassa is known to possess a branched respiratory system consisting of the standard cytochrome chain and a cyanide-insensitive alternate oxidase. In the present experiments, the physiological function of the alternate oxidase has been analyzed by taking advantage of a number of cytochrome-deficient mutants, particularly poky f. Respiration, cellular ATP levels, and growth have been examined under the influence of three classes of inhibitors: inhibitors of the cytochrome chain (antimycin, cyanide), an inhibitor of the laternate oxidase (salicyl hydroxamic acid), and an uncoupling agent (carbonyl cyanide m-chlorophenylhydrazone). The results indicate that the over-all efficiency of the alternate oxidase in producing ATP and supporting growth is much less than that of the cytochrome chain. Depending upon the amount of oxidative phosphorylation at Sites II and III in the cytochrome chain, which varies from strain to strain, the efficiency of the alternate oxidase relative to that of the cytochrome chain ranges from 13% in wild type Neurospora to 18 to 21% in poky f, 35% in mi-3, and 57% in cyt-2. A comparison of the short term effects of cyanide and carbonyl cyanide m-chlorophenylhydrazone on cellular ATP in poky f suggests that, during respiration through the alternate oxidase, ATP can be produced both by substrate-level phosphorylation (accompanying glycolysis and the oxidation of alpha-ketoglutarate) and by oxidative phosphorylation at Site I. When cells are grown on sucrose, as much as 22% of ATP synthesis in the presence of cyanide occurs at Site I. When cells are grown on acetate to diminish the rate of glycolysis, the contribution of Site I becomes proportionately larger. Both the growth experiments and the short term inhibitor experiments reveal that ATP levels in Neurospora are kept high be a feedback process which depresses ATP breakdown (and growth) very quckly after ATP synthesis is inhibited. Thus, poky f grows more slowly that wild type Neurospora and is inhibited still further when either the cytochrome chain or the alternate oxidase is blocked. Under all of these conditions, however, cellular ATP in poky f is maintained at a high level (about 3 mmol per kg of cell water, slightly above the values measured in the wild type strain).

Item Type:Article
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Rees, Douglas C.0000-0003-4073-1185
Additional Information:© 1975 American Society for Biochemistry and Molecular Biology. Received for publication, May 20, 1974. This work was supported by Research Grants GM-15761 and GM-15858 and by Research Career Development Awards GM-20163 and GM-20164 from the National Institute of General Medical Sciences. The authors are indebted to Dr. Alan Lambowitz and Dr. Dietrich Gradmann for their many helpful discussions.
Funding AgencyGrant Number
National Institute of General Medical SciencesGM-15761
National Institute of General Medical SciencesGM-15858
National Institute of General Medical SciencesGM-20163
National Institute of General Medical SciencesGM-20164
Issue or Number:2
Record Number:CaltechAUTHORS:20150210-101019010
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Official Citation:C W Slayman, D C Rees, P P Orchard, and C L Slayman Generation of adenosine triphosphate in cytochrome-deficient mutants of Neurospora. J. Biol. Chem. 1975 250: 396-408
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54662
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Deposited On:10 Feb 2015 18:27
Last Modified:03 Oct 2019 07:59

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