The Cyanide-Resistant, Alternative Path in Higher Plant Respiration

The functional and thermodynamic characteristics of the ubiquinolcytochrome (Cyt) c oxidoreductase in a Cyt b/c,-enriched fraction (defined S-1) isolated from Jerusalem artichoke mitochondria (JAM) (Helianthus tuberosus), have been analyzed. Fraction S-1, obtained through deoxycholate-KCI fractionation procedure, contained one Cyt ofc type (formally cl with Em7.0 of +240 millivolts), two b type Cyt with Em7.. values of +100 and -25 millivolts, ferredoxin-like centers presumably linked to succinic-and NADH-dehydrogenases, and a Rieske-type iron sulfur center (gy = 1.89). The ubiquinol-dependent Cyt c reduction by fraction S-I showed sensitivity to antimycin A, myxothiazol, and n-2-hepthyl-1-hydroxyquinoline N-oxide with I50 of 12 nanomolar, 30 nanomolar, and 0.1 micromblar, respectively. Oxidation-induced extra b type reduction, a widespread phenomenon of bacterial and mitochondrial respiratory systems, has also been observed in both intact mitochondria and S-1 fraction. The data seem to blur previous experiments in which both spectral and functional differences between higher plant and mammalian mitochondria have been underlined.The respiratory chains of eukaryotic and prokaryotic systems are an assembly of more than twenty discrete carriers ofelectrons together with an unspecific number of structural peptides (30). While the function of the respiratory chain as an oxidationreduction driven proton-pump is now accepted (30), the structural basis underlying this function is only partially understood (30). Owing to this, respiratory and photosynthetic electron transport in mammalian mitochondria, photosynthetic bacteria, blue-green algae, and chloroplasts have been analyzed throtgh isolation and characterization of multiple redox complexes (12). However, little effort has been made to try to understand both structural and redox properties of respiratory complexes from plant mitochondria. Published experimentation dealt with partial purification of either the b type Cyt from mung bean (Phaseolus aureus) and potato tuber mitochondria (8,13) (14). Evidence for the presence of a Rieske-type iron-sulfur center (gy = 1.89) is also presented.

mentioning

confidence: 87%

Functional Characterization and Partial Purification of the Ubiquinol-Cytochrome c Oxidoreductase from Higher Plant Mitochondria (Helianthus tuberosus)

Esposti¹,

Flamini²,

Zannoni³

1985

“…uptake in the presence of inhibitors, namely KCN (to inhibiit the Cyt path) and/or SHAM (to inhibit the alternative pathway) as suggested by Laties (1982) and Siedow and Berthold (1986). The relative expression of these two pathways is calculated using the equations described earlier (AzcÓn-Elieto et al, 1987).…”

Section: Analysis Of Cyanide-resistant Respirationmentioning

confidence: 99%

“…The present report is from our study of the respiratory characteristics of GCP using respiratory inhibitors such as KCN and SHAM, which block the Cyt and altemative pathway, respectively (Laties, 1982;Siedow and Berthold, 1986). MCP prepared from the same leaves are included for comparison.…”

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confidence: 99%

High Mitochondrial Activity but Incomplete Engagement of the Cyanide-Resistant Alternative Pathway in Guard Cell Protoplasts of Pea

Vani

Raghavendra

1994

l h e respiratory properties of guard cell protoplasts (CCP) were examined in comparison with those of mesophyll protoplasts (MCP) from the same leaves of pea (Pisum sativum 1. cv Arkel). l h e rates of respiratory O, uptake by CCP were extremely high (280 pmol mg-' Chl h-') and were severa1 times greater than those of MCP. On the other hand, the rates of photosynthetic O, evolution by CCP were similar to those of MCP. Also on the basis of protoplast volume, the respiratory rates of CCP were higher: more than three times those of MCP. l h e enzymes of the tricarboxylic acid cycle, per unit protein or unit protoplast volume, had a 2-to 5-fold higher activity in CCP than in MCP, indicating an enrichment of mitochondrial activity in CCP relative to that in MCP. Respiratory inhibitors were used to asses the activity of the cytochrome (cyanide-sensitive) and alternative (cyanide-resistant) pathways in CCP and MCP. l h e inhibition of respiration by KCN or antimycin A was more in CCP than that in MCP. l h e marked inhibition of respiratory 0, uptake by salicylhydroxamic acid in the presence of KCN showed the presence of the cyanide-resistant pathway in CCP. l h e activity of the cyanide-resistant electron transport path constituted only one-third of total respiration in CCP but accounted for two-thirds of respiration in MCP. l h e alternative pathway was not completely engaged in CCP but reached its full capacity in MCP.

“…In spite of its having been studied for the past 40 years, the cyanide-resistant (alternative) 02 uptake pathway in plant mitochondria has yet to be fully elucidated (12,20 …”

Section: Introductionmentioning

confidence: 99%

“…Taken together, these results suggest a model for the interaction of the alternative pathway with the cytochrome pathway. In this modeL the butyl gallate binding site (alternative oxidase) is a constitutive component in those mitochondria that are capable of developing the alternative pathway, and the binding-sites associated with a second, inducible component that functions to couple the oxidase to the cytochrome pathway.In spite of its having been studied for the past 40 years, the cyanide-resistant (alternative) 02 uptake pathway in plant mitochondria has yet to be fully elucidated (12,20 …”

mentioning

confidence: 99%

Binding of Butyl Gallate to Plant Mitochondria

Stegink

Siedow²

1986

ABSTRACT[I4Cjbutyl pllate was used in binding studies to investigate the cyanideresistant respiratory pathway in mitochondria isolated from a variety of sources displaying varying levels of cyanide resistance. Highly cyanideresistant mitochondria were isolated from aroid spadices, while moderately cyanide-resistant mitochondria were isolated from either mung bean (Vigna radiata L.) hypocotyls or carbon dioxide/oxygen/ethylene-treated tubers. Totally cyanide-sensitive mitochondria were isolated from untreated tubers and rat liver. With one exception, all the plant mitochondria showed a reversible butyl gallate binding site which saturated at a level of 1.0 to 2.0 nanomoles per milligram protein. The exception, freshly harvested white potato tubers (<1 month from harvest), showed little specific butyl pilate binding, and also showed no appreciable induction of the cyanide-resistant pathway following carbon dioxide/ oxygen/ethylene treatment. Only a low level, linear binding, well below that seen with plant mitochondria, was observed with rat liver mitochondria. Taken together, these results suggest a model for the interaction of the alternative pathway with the cytochrome pathway. In this modeL the butyl gallate binding site (alternative oxidase) is a constitutive component in those mitochondria that are capable of developing the alternative pathway, and the binding-sites associated with a second, inducible component that functions to couple the oxidase to the cytochrome pathway.In spite of its having been studied for the past 40 years, the cyanide-resistant (alternative) 02 uptake pathway in plant mitochondria has yet to be fully elucidated (12,20