Subunits of Bakers' Yeast Cytochrome b2 ( l ‐Lactate Cytochrome c Oxidoreductase)

After reduction and carboxymethylation, crystallized cytochrome b2 has been separated by gel filtration into two main fractions and a minor one. The latter is probably an aggregate. The apparent molecular weight of the major fractions has been determined by acrylamide gel electrophoresis in the presence of 0.1% sodium dodecyl sulfate, and found to be of the order of 36000 and 21000. Their amino acid composition is very different. Their sum gives a composition in good agreement with the composition corresponding to the minimum molecular weight of unfractionated cytochrome b2. On the basis of the evidence presented in the paper and of the known molecular weight of crystallized b2, it is suggested that the protein is an oligomer of the type (αβ)4.