ABSTRACT:
Succinate-DCPIP oxidoreductase (SO) and NADH-fumarate oxidoreductase (FR) activities were found to be membrane-bound in Achatina achatina mitochondria.2.2. The SO/FR and FR/SO ratios of submitochondrial particles (SMP) were found to change from 1.4 and 0.72 respectively on the day of preparation of SMP to 0.32 and 3.16 respectively after storage for 7 days at 0–4°C.3.3. The Michaelis constants () for fumarate and succinate were 12.5 mM and 40 mM respectively, and the maximum velocities () for fumarate reduction and succinate oxidation by SMP were 1.1 μmol/min/mg protein and 1.25 μmol/min/mg protein respectively.4.4. The ratio of (succinate)/ (fumarate) was calculated to be 3.2.5.5. The optimum pH for both enzymic activities was pH7.5–7.6.6.6. Succinate-DCPIP oxidoreductase activity of SMP was stimulated by Br−, NO−3, Cl−, I− and acetate ions at pH 7.6 but not at pH 6.4 whereas these ions had no effect on NADH-fumarate oxidoreductase activity at pH 6.4 and pH 7.6.7.7. NADH-fumarate oxidoreductase activity of SMP was inhibited 45–55% by 100 μM rotenone and 7–80% by 1 mM malonate but succinate-DCPIP oxidoreductase activity was inhibited 80% by 1 mM malonate and was insensitive to rotenone.8.8. Succinate oxidation by SMP was stimulated by 2 mM ATP while fumarate reduction was stimulated by 2 mM ADP + Pi.9.9. Succinate-DCPIP oxidoreductase activity of SMP was completely inhibited by 10 μM oxaloacetate whereas up to 100 μM oxaloacetate had no effect on NADH-fumarate oxidoreductase activity, but in the presence of 1 mM oxaloacetate about 33% inhibition of the latter enzymic activity was observed.10.10. In the presence of low concentrations of oxaloacetate (< 2.0 μM) inhibition of succinate-DCPIP oxidoreductase activity was competitive and had an inhibitor constant () of 1.05 μM.
Comparative biochemistry and physiology. B, Comparative biochemistry 01/1982; 71(2):181-185. DOI:10.1016/0305-0491(82)90238-3
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