ELECTRON-SPIN-RESONANCE STUDIES OF NITROSYL HEMOGLOBIN IN HUMAN LIVER, COLON AND STOMACH TUMOR-TISSUES

Iron nitrosyl haemoglobin (HbFeNO) gives well defined ESR spectra, and can be detected at room temperature, in contrast with most transition metal complexes of biological importance. This is because the unpaire d electron remains strongly localised on the NO ligand. It is of impor tance because it proves the formation of nitric oxide, which unfortuna tely cannot be detected directly by ESR spectroscopy. We have studied a range of tissues taken from human liver, colon and stomach tumours w hich have been directly frozen to 77K and studied at 77K. The results show that formation of HbFeNO is rare in tissue adjacent to tumour tis sue (''peripheral tissue''), but is always found in necrotic central r egions, if present. However, in several cases, HbFeNO was also detecte d in tumour tissue which was not necrotic. Two factors contribute to t he formation of this complex. One is the presence of ''free'' NO molec ules in the cellular regions, and the other is the presence of deoxyfe rrohaemoglobin, since neither ferrihaemoglobin nor oxyhaemoglobin reac t to give this complex. [For systems containing myoglobin these commen ts include the possibility of the formation of nitrosylmyoglobin, whic h gives very similar ESR spectra.]