Some EPR signals in tumour tissue.

Normal and tumour tissues from rats, blood from normal and tumour bearing rats, and normal human blood were examined using the electron paramagnetic resonance (epr) technique. At low temperature a triplet epr signal, which is known to be produced by a NO-haemoprotein complex, was detected in some tumour samples and in decaying normal liver. At room temperature all of the tumour samples examined gave a doublet signal. This signal was also detected in blood but not in other normal tissues. The signal has a g value of 2·0054 ± 0·0002 and a hyperfine splitting of 1·80 ± 0·05 G and is assigned to the ascorbyl free radical. Model experiments suggest that the appearance of detectable concentrations of this radical result from a disturbance of the normal state of the ascorbic acid, dehydroascorbic acid redox system. It was verified that cell division is not responsible for the ascorbyl radical although autolysis may be involved. A possible relationship between the formation of ascorbyl radicals and other paramagnetic species in tumours is discussed.