UBIQUINONE REDOX BEHAVIOR IN PLANT-MITOCHONDRIA DURING ELECTRON-TRANSPORT

The redox poise of the ubiquinone pool during electron transfer in iso lated soybean mitochondria has been compared using two different proce dures: the rapid organic extraction of ubiquinone followed by quantifi cation of the oxidized and reduced forms using high-pressure liquid ch romatography and an electrochemical technique that measures ubiquinone reduction voltametrically. The goal of these studies was to rigorousl y test the use of the voltametric technique to monitor the redox statu s of ubiquinone during the course of mitochondrial electron transfer. The linear relationship between the two methods confirms the reliabili ty of the data obtained with the voltametric technique; however, redox inactive pools of ubiquinone were detected with the HPLC technique. W e also quantified the absolute amounts of the ubiquinone homologues ub iquinone-9 and ubiquinone-10 in mitochondria isolated from different s oybean tissues and compared their behavior during electron transfer in the presence and absence of pyruvate, an allosteric effector of the c yanide-resistant electron transfer pathway. Both homologues belong to a common redox-active pool in the inner mitochondrial membrane. The re sults indicate that ubiquinone can be a limiting component of electron transfer through the cyanide-resistant pathway, particularly in roots where its concentration is much lower than in cotyledons. (C) 1995 Ac ademic Press, Inc.