OXIDATION OF SUBSTANCES OF BIOLOGICAL IMPORTANCE 223 



(Fig. 3) than in neutral solutions (Fig. 4) or acid solutions (Fig. 5). An 

 examination of the absorption spectrum curves shows that in the region 

 of light absorption by the tyrosine residue (2800 A) x-rays produced 



0.6- 



0.5 



0.4- 



c»5 



0.3- 



0.2 



2.5 



3.0 

 xlO^A 



3.5 



Fig. 4. Effect of x-ray irradiation on the protein moiety of ferricytochrome c, dis- 

 solved in 0.005 M phosphate buffer, pH 7.72. Abscissa: Wavelength in angstrom 

 units; ordinate: optical density E. 



an increased absorption. The effect of x-rays on the porphyrin nucleus 

 as observed by light absorption in the ultraviolet was also influenced 

 by the H'^-ion concentration of the solution, as can be seen on observing 



