Scientia Sinica

No. 1 WANG, TSOU, & WANG: STUDIES ON SUCCINIC DEHYDROGENASE I | 83

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Reciprocal of KsFe(CN)s concentration, mM!

Fig. 5. Effect of ferricyanide concentration on the activity of succinic dehydrogenase. The reaction mixture contained 52 mM phosphate buffer, pH. 7.8, 30mM of succinate, the required’ concentration of ferricyanide and 0.0687 mg enzyme N. The enzyme preparation used had a specific activity of 17 and the reaction was carried out at room temperature (about 30°C), The reciprocals of the reaction velocities- (optical density decrease at 420 my per 5 min.) are plotted against the reciprocals of initial ferricyanide concentrations according to Lineweaver and Burk.

With phenazine methosulphate as acceptor, the reaction rate, in terms of succinate oxidation, is much more rapid than with ferricyanide. Methylene blue js much less efficient as an acceptor than ferricyanide and with cytochrome c, the reaction rate is barely measurable. These results are summarized in

Table 7.

Table 7. A Comparison of Different Acceptors,

Acceptor Concentration, mM| Temperature, °C | Relative(S) Activity Qos (el O2/ hr/mg protein ) Ferricyanide 2, 38 3600 Phenazine metho- 25 38 8.5 31000sulphate () Methylene blue) 0.45 25 1/7 Cytochrome c(®) 0.037 25 | 1/200

Measured exactly as cescribed by Kearney et all28),

Q) (2) Measured anaerobically. (3) Relative activites are calculated as the number of moles of succinate oxidized per minute

and expressed relative to the activity with ferricyanide which is arbitrarily taken as unity.