THE PREPARATION OF CRYSTALLINE FORMS OF FERRICYTOCHROME B2 AND FERROCYTOCHROME B2

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Abstract
A modified procedure is described for obtaining crystalline Type I-ferrocyto-chrome b2 from air-dried baker''s yeast. The addition of magnesium sulphate facilitates crystallization, and EDTA in high concentrations prevents it. A procedure for obtaining crystalline Type I-ferrocyto-chrome b2 from a butan-1-ol-acetone-dried powder of yeast is described. After isolation in crystalline form, Type I-ferrocytochrome b2 is readily recrystallized either at low ionic strength or by acetone precipitation. According to the conditions of acetone precipitation, a number of crystalline forms of Type I-ferrocytochrome b2 were obtained. A procedure is described for obtaining crystalline Type I-ferricytochrome b2. The addition of GSH does not reduce the haematin group but the haematin group is partly reduced by a large excess of ascorbic acid. After removal of the DNA component by slow fractiona-tion of the protein with ammonium sulphate, Type n-ferrocytochrome b2, and Type II-ferricytochrome b2 may be isolated in crystalline form at low ionic strength. Crystals of Type II-ferrocytochrome b2 up to 0.5 mm. across may be obtained. The crystalline form differs considerably from that of Type I-ferrocytochrome b2. Less perfect crystals of Type n-ferrocytochrome b2 are obtained by slow precipitation with ammonium sulphate or with acetone.