Scientia Sinica

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No. 1 WANG, TSOU, & WANG: STUDIES ON SUCCINIC DEHYDROGENASE I ~ 7

PRopERTIES OF THE PURIFIED ENZYME

Stability. The solubilized enzyme is unstable in the presence of air even when stored at -I5°C. Versene gives no protection whereas succinate protects only to a slight extent against this spontaneous inactivation. Sucrose, glycerol, and glycine are more effective than succinate in protecting the enzyme against air inactivation. These results are summarized in Table 3. However, the

Table 3, Stability o£ Solubilized Succinic Dehydrogenase under Various Conditions,

eee — ee

Aerobic or Anaerobic ecg pate Protective Agent | Time os aoe ey aa Aerobic 0 — 3 | 20—26 Aerobic =15 | — eee 13s - 20-26 Aerobic. 0 Succinate, 10 mM ~ | 3 - 35 Aerobic —15 Succinate, 10 mM 3 35 Aerobic —15 Sucrose, 300 mM 3 | 100 Aerobic —15 Sucrose, 300 mM 30 | | 50 Aerobic —15 Glycerol, 260 mM i 3 90 Aerobic —15 Glycine, 20 mM 3e, 70 Aerobic 0 Versene, 3.4 mM | 3 | 17 Aerobic 0 Versene, 0.34 mM 3 | 17 Anaerobic 0 == | 60 100

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enzyme is perfectly stable when kept under vacuum or under nitrogen in the complete absence of oxygen; one sample has been kept for 2 months under vacuum without any appreciable loss in activity.

An enzyme preparation which has lost its activity in air cannot be re activated by treatment with H,S, 2,3-dimercaptopropanol or reduced glutathione under vacuum, showing that the inactivation of the enzyme is not simply due to air oxidation of essential sulfhydryl groups.

Table 4 shows that the enzyme is stable only in a narrow pH range in the absence of succinate even when kept under nitrogen. In the presence of succinate, the enzyme is stable between pH 5.6-9.5.

Activation of succinic dehydrogenase by succinate. Both the particlebound and the solubilized enzyme can be activated by incubation with succinate. As a rule, an increase in activity of over 100% has usually been observed (Table 5). The highly purified enzyme still retains this property.