EFFECT OF TEMPERATURE ON THE PATHWAYS OF NADH-OXIDATION IN BROAD-BEAN MITOCHONDRIA

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 concentration, 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.degree. C occurred only with activities linked to energy conservation. 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 of a superimposition of 2 branches of electron transport, which were separated by different sensibilities to rotenone. A characteristic temperature dependency of the respiratory control and 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 2 branches. The temperature dependency of the oxidation of extra-mitochondrial NADH and of succinate differs remarkably from that of the oxidation of matrix-NADH. Apparently the rotenone-resistant oxidation of matrix-NADH and the oxidation of external NADH are mediated via different pathways with individual regulation sites.