Effect of Roentgen Radiation on Solutions of Tyrosine, Phenol, and Tryptophane

IN a preceding article (1) we have described how the effect of roentgen radiation on weak aqueous solutions of colored substances was studied in our laboratory. The same general arrangements have been used for the study of the effect on some other compounds. The amount of radiation absorbed by the solutions was also determined in the same manner as before, and was found to be about 8 kilo-roentgens per hour. Tyrosine was chosen as one of the first substances to be studied because of its relatively simple configuration and its sensitivity to certain quantitative tests. For the first experiments Folin's phenol reagent (molybdate method) (2) was used to determine how much tyrosine was destroyed by the radiation. The tyrosine was extracted and purified by one of us (A. L.). The results of these experiments were published in 1928 (3). It was found that the total change produced by the radiation, as measured in this way, was proportional to the dose absorbed by the solution of the tyrosine when this was varied from 1.0 mg. to 0.02 mg. per c.c. of solution. Some measurements with tyrosine from the Phanstiehl Company have since been carried out. A straight line relation between the roentgen dose and the amount of the tyrosine changed, as determined by the molybdate method, was again obtained. The values were, however, slightly though consistently smaller than before. It is possible that substances produced by the radiation may also contribute to the color reaction utilized in the molybdate method, which, therefore, may not give the exact amount of tyrosine disappearing. More tyrosine should then have been affected than the measurements indicate. Although the same objection may be made to other tyrosine methods it seemed advisable to use one other test for comparison. Samples from the same tyrosine solutions were, therefore, examined both with the molybdate reagent and Millon's reagent (2). The latter indicated a greater change than the former, e.g., 17 per cent against 13 per cent in one experiment. It is difficult to determine what changes are produced by the radiation. Perhaps intermediary products are formed, which, again, are attacked and split up. They may, therefore, be present in very minute quantities and would not be easy to detect, when it is considered that the original concentration of the tyrosine was only 0.02 mg. per c.c. of solution. Perhaps different tyrosine molecules are changed in different ways; some may be aggregated to condensation products, others may be decomposed. It seemed probable that ammonia would be given off, and we tried to determine if such were the case. Fifty c.c. of a 0.02 per cent solution of tyrosine in 1 per cent H2S04 was irradiated for 30 hours. A test for ammonia in this solution with Nessler's reagent was positive, but the color produced might be due to traces of other substances (e.g., formaldehyde or hydroquinone).