Scientia Sinica

84 SCIENTIA SINICA Vol, V

It can be seen from Table 7 that, with phenazine methosulfate as acceptor,

our best preparation has a Qo, of 31000 which is over twice that reported by Singer, Kearney, and Zastrow!™”!.

Effect of pH on enzyme actwity. Fig. 6 shows the effect of pH on the solubilized enzyme. In phosphate buffer, the optimal pH is 7.8.

0.20

—Ad

0.10

6 7 . 8 9 10 pH

Fig. 6. Effect of pH on the activity of succinic dehydrogenase. The reaction mixture contained 30 mM succinate, 2 mM of ferricyanide, 0.079 mg of enzyme N (specific activity, 41) and 53 mM of phosphate at the required pH. Room temperature about 28°C. The exact pH value of each reaction mixture was determined after 10 min, reaction by the glass electrode. Effect of temperature on enzyme activity. The effect of temperature on the enzyme activity before and after succinate activation has also been studied and the Arrhenius plots obtained are shown in Fig. 7. It can be seen that the activation energy remains constant only in a narrow temperature range and that at higher temperatures activation energy values become lower. ‘The enzyme seems to have the same activation energy before and after succinate

activation, although it appears that for the substrate activated enzyme the