The enzymic composition of nuclei isolated from radio-sensitive and non-sensitive tissues with special reference to catalase activity.

The many attempts to demonstrate early activation or inactivation of specific enzymes as a consequence of exposure to ionizing radiation in vivo have not succeeded in disclosing the biochemical origin of the radiobiological lesion. This failure may be due to localization of the primary biochemical events at certain sites within the cell, for in such circumstances the earliest changes might escape detection in studies on whole tissues or homogenates. Such localized intracellular responses have been observed in the behaviour of mitochondrial deoxyribonuclease II (GoutierPirotte & Thonnard, 1956) and in the uptake of 32p into liver ribonucleic acid (Payne, Kelly & Entenman, 1952). It seemed likely that in view of the marked disturbance of nuclear function after irradiation, a comparison of the enzymic complement of the nucleus in radio-sensitive (i.e. those tissues which show early histological deterioration after exposure to sublethal radiation) and nonsensitive tissues might provide a clue to the nature of the primary biochemical lesion. About thirty nuclear enzymes are known, but unfortunately many of these have been described in tissues from slaughter-house animals which are not suitable for radiobiological studies. The rat, which is very satisfactory for such purposes, has been used for the present work. A number of nuclear enzymes have been assayed and their activities expressed on the basis of deoxyribonucleic acid phosphorus content as recommended by Gray & Deluca (1956).