Abstract
1. Calf thymus nuclei isolated in 0.25M sucrose-3mM CaCl2 were purified by density gradient centrifugation and Triton X-100 treatment. The nuclei thus obtained seem to be rather pure, judging from their chemical composition and the activities of mitochondrial and microsomal marker enzymes.
2. Spectrophotometric studies revealed that the purified nuclei contained cytochromes of the b and c type at concentrations not explicable as due to contamination with mitochondria and microsomes.
3. Further evidence was provided that the c-type cytochrome in isolated nuclei is not mitochondrial in origin.
4. Nuclear cytochromes could be reduced with NADH and NADPH, suggesting that a respiratory chain involving these cytochromes is functioning in calf thymus nuclei.
The authors are indebted to Sankyo Company for their kind gift of yeast cytochrome c.
