Scientia Sinica

86 SCIENTIA SINICA Vol. V:

that it has an absorption maximum at 415 mg and shoulders at 460 and 360 my. The addition of succinate causes partial reduction of the enzyme as evidenced by the slight decrease in light absorption particularly at 460 mz. The enzyme solution is almost completely bleached by the addition of Nadithionite, indicating extensive reduction of the enzyme. The differential spectrum between the oxidized and reduced enzyme shows a distinct maximum at 460 mz. The enzyme is non-fluorescent.

Optical density

J50 400 450 500 550 Wavelength, mp

Fig. 8. Absorption spectra of succinic dehydrogenase. Light absorption measured in Beckman spectrophotometer with 5 mm cuvette, Curve I shows the absorption spectrum of a highly purified succinic dehydrogenase (same enzyme preparation as used in Fig. 3) with a concentration of 1 mg enzyme N/ml. To 1.5 ml of the above solution was added 0,02 ml of 0.8 M succinate and the resulting spectrum is shown by curve II (concentration change by dilution corrected). Curve III shows the fully reduced enzyme solution after the addition of sodium = dithionite. Curves I-II and [JIT are obtained by subtraction of curves II and II]. respectively from curve I.

Iron ana flavin content. When the highly purified enzyme solution is digested with crystalline trypsin and crystalline chymotrypsin, the colour gradually changes from amber to a bright lemon yellow, the activity is lost and it now shows distinct greenish yellow fluorescence, the intensity of which varies with the pH of the medium (Fig. 9). Highly purified enzyme preparation ‘also contains iron. Both the iron and the flavin contents increase with the specific activity of the enzyme in the later stages of purification.