title: Effect of temperature on the pathways of NADH-oxidation in broad-bean mitochondria.
abstract: 1. Respiration rates of broad-bean (Vicia faba) mitochondria were studied as a function of temperature. Arrhenius plots of all membrane-bound enzymes, as obtained with saturating substrate concentrations, revealed a break in the lower temperature range. That break was considered to indicate a phase transition of membrane phospholipids, characteristic for chilling-sensitive plants. A second discontinuity at 30°C occurred only with activities linked to energy conservation. - 2. The activation energies for the oxidation of NAD(+)-linked substrates differ between states 3 and 4. State 3 respiration of NAD(+)-linked substrates is the result a superimposition of two branches of electron transport, which can be separated by different sensibilities to rotenone. A characteristic temperature dependency of the respiratory control, as well as a shift of the low temperature break in the Arrhenius plot toward a higher temperature after state 4 to state 3 transition, are calculated to be caused by the superimposition of the two branches. - 3. The temperature dependency of the oxidation of extra-mitochondrial NADH and of succinate differs remarkably from that of the oxidation of matrix-NADH. It has been concluded that the rotenone-resistant oxidation of matrix-NADH and the oxidation of external NADH are mediated via different pathways with individual regulation sites.
authors.affiliation: Botanisches Institut der Universität, Kirschallee 1, D-5300, Bonn 1, Federal Republic of Germany.
authors.forename: R
authors.initials: R
authors.lastname: Marx
authors.forename: K
authors.initials: K
authors.lastname: Brinkmann