. Biological structure and function; proceedings. Biochemistry; Cytology. 128 BRITTON CHANCE The succinate-linked mitochondrial pyridine nucleotide is postulated to be separated from the remainder of the DPN by a compartment—possibly the cristae and matrices of the mitochondria are involved. This com- partmentation implies that electrons donated by a DPN-linked substrate cannot readily enter the succinate-linked pyridine-nucleotide pool while those from succinate can. Succinate -^ Fumarate. Malate -^ 3X~P+3I 3ATP+ 3X dbc Fig. 12. Schematic diagram of electron-transfer pathways in respiratory c
. Biological structure and function; proceedings. Biochemistry; Cytology. 128 BRITTON CHANCE The succinate-linked mitochondrial pyridine nucleotide is postulated to be separated from the remainder of the DPN by a compartment—possibly the cristae and matrices of the mitochondria are involved. This com- partmentation implies that electrons donated by a DPN-linked substrate cannot readily enter the succinate-linked pyridine-nucleotide pool while those from succinate can. Succinate -^ Fumarate. Malate -^ 3X~P+3I 3ATP+ 3X dbc Fig. 12. Schematic diagram of electron-transfer pathways in respiratory chain involving succinate-linked pyridine-nucleotide reduction. This diagram is similar to those presented earlier [i, i8, 19] and includes the quinone component [20]. (Reproduced with permission of the Jotirnal of Biological Chemistry.) 2. Energy-linked cytochrome oxidation Since the preceding considerations demonstrate reverse electron trans- fer in a branch of the respiratory chain, we have actively considered the possibility that flavoprotein may be oxidized in DPN reduction as indi- cated in Fig. II, provided experimental conditions could be arranged so that pyridine nucleotide was oxidized and flavoprotein reduced. A suitable condition for this can be obtained by antimycin-A or quinoline oxide inhibition of the respiratory chain, reinforced by hydrosulphide inhibition of the oxidase. The plan for such an experiment is indicated by Fig. 8. If electrons have already been transferred up to the level of cytochrome h and flavoprotein, so that the flavoprotein involved in DPN reduction is already reduced, then indeed addition of ATP should be all that is needed to cause pyridine-nucleotide reduction with a concomitant oxidation of flavoprotein. It has been observed in pigeon-heart mitochondria that treatment of the aerobic suspension with 4 niM succinate and sufficient. Please note that these images are extracted from scanned page images that may have been digitally enhanced f
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