Abstract
1. Cytochrome 552 and cytochromoid c were extracted from Rhodopseudomonas palustris cells, purified and obtained in crystalline form. 2. Extinction ratios and amino acid compositions of the two pigments are reported. 3. When subjected to starch-gel electrophoresis in borate buffer, pH8.8, each pigment migrated towards the cathode; oxidized cytochromoid c migrated more rapidly than its reduced form. 4. By a determination of electrophoretic mobilities in buffers of I0.1 by using the moving-boundary method, the isoelectric point of cytochrome 552 was found to be at pH10.6 and that of cytochromoid c at pH9.7. 5. As obtained, cytochrome 552 was non-autoxidizable; cytochromoid c was autoxidizable but became considerably less so on alkaline treatment. 6. Discussion of the results includes a consideration of the isoelectric points of the pigments in terms of their amino acid composition.