TCA Cycle in Plant MitochondriaThe tricarboxylic acid (TCA) cycle in mitochondria catalyses the complete oxidation of organic acids to CO2 and the reduction of NAD(P) in the mitochondrial matrix and also the partial oxidation of organic acids leading to some CO2 release, NAD(P) reduction and the release of 4,5 and 6 carbon intermediates for biosynthesis in other parts of the cell. This pathway is made up of 9 major enzyme complexes which vary in native size from 120 kDa to 6,000 kDa. Most of our knowledge about these enzmyes comes from work in mammalian, yeast and bacterial systems, while in plants many of them have only received elementary levels of analysis. We have been specially interested in the two largest protein complexes pyruvate dehydrogenase complex (5,000 kDa) and 2-oxoglutarate dehydrogenase complex (3,000 kDa) which both catalyse the release of CO2 and the reduction of NAD to NADH. These enzymes contain a complex oligometric structure consisting of 3 different enzyme activities that combine to catalyse a single reaction with a number of bound intermediates handed from one enzyme to another. Both these enzymes are rapidly inhibited by the products of lipid peroxidation and this effect has been linked to the decline in respiration of heart tissues following ischaemia in mammals. We are now investigating the effect of oxidative stress in plants on the function of these enzymes.。