Effect of the oxidation of glycine and Krebs cycle substrates on cytochrome activity and alternative pathways of mitochondria from leaves of Pisum sativum L

Isolated mitochondria from adult leaves of Pisum sativum had the capacity to oxidize simultaneously glycine and several substrates of the Krebs cycle (e.g. malate, succinate, citrate, 2-oxo-glutarate), either in the presence of ADP (state three) or in the absence of ADP (state four). The sensitivity of the mitochondrial respiration to inhibitors of the cytochrome (e.g. antimycin A) and the alternative (e.g. salicylhydroxamic acid, SHAM, and tetraethylthiuram disulfide, disulfiram) pathways varied depending on the substrate(s) being used. For instance, the rate of oxygen uptake resistant to antimycin A, which is an estimate of the capacity of the alternative pathway, varied depending on whether glycine was added or not to a medium with malate and succinate. The state four rate of oxygen consumption in the presence of malate or succinate was greatly stimulated by the addition of glycine, and vice versa. This stimulation was apparently mediated by the alternative pathway. The results suggest that part of the electron transport capacity (including the alternative pathway) of these mitochondria is specifically associated with glycine oxidation, and therefore with photo-respiration.