Enzyme Alteration by Ionizing Radiation

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Abstract
The increase of intracellular yeast catalase activity (Euler effect) induced by exposure of the cells to X- and gamma-radiation was shown to be due to a change in the physical state of the enzyme (enzyme alteration). Calculation of the target size for the alteration process yields a value corresponding to a substance of molecular weight 2 x 106. This might be ribon-ucleic acid which is known to be intimately associated with yeast catalase. Calculations from the dose of X-radiation needed to inactivate fully altered yeast catalase lead to a value of 250,000 for the molecular weight of that enzyme. The results show how ionizing radiation can affect the enzymatic activity of the more radiosensitive portions of the cell, leading to a disturbance of the physiological balance of the cell before appreciable direct inactivation of the enzyme itself occurs.