EFFECT OF RADIATION ON PROTEINS 311 



Although a decrease in solubility is the most widely investigated, 

 and probably the most important result of radiation, many other changes 

 have been noted in radiated proteins which may be associated with the 

 physicochemical change somewhat loosely designated as denaturation, 

 or may be independent of it. These changes will be mentioned briefly 

 below. 



Odor. — During irradiation proteins acquire a characteristic, rather 

 unpleasant, burnt odor similar to that produced on exposing the skin 

 to an ultra-^'iolet arc. In the case of egg albumin it is independent of 

 the purity being just as evident in material recrystallized five times as 

 in a crude preparation. Mond (39, 40) found purified serum albumin 

 developed less smell than pure egg albumin. When dried crystalline 

 egg albumin is exposed to an ultra-violet arc, there is no odor until the 

 radiated material is dissolved in water. 



Color. — All proteins, whether dry or in solution, become more or less 

 yellow under radiation. The color change seems to parallel the produc- 

 tion of an odor and the two occur under the same conditions. 



Optical Rotation. — Many authors have noted the fact that proteins 

 show definite increases in levorotation after radiation. Both Chalupecky 

 (6) and Young (63) reported this result with egg albumin. Stedman 

 (54) found increases in levorotation in edestin in 10 per cent NaCl 

 and in gliadin in 70 per cent alcohol (see also Spiegel- Adolf (49)). 



Viscosity. — An increase in viscosity is marked after radiation in the 

 case of globulins (49), the change being greater for euglobulins than for 

 pseudoglobulins and greater for pseudoglobulins than for albumins. 

 Young (63) noted a rise in viscosity in radiated egg albumin but Clark (10) 

 failed to find any at pH 6.0. This has been taken by some authors as 

 evidence of a change in state of aggregation with radiation (39, 40). 



Surface Tension. — After radiation there is a decrease in surface tension 

 which, like the increase in \iscosity, is greatest in the euglobulins and 

 least in the albumins (49), although the surface-tension change is more 

 marked in albumins than the viscosity change (10). 



Temperature of Coagulation. — Chick and Martin (7, 8) have pointed 

 out that the coagulation temperature is not a fixed property of proteins 

 and depends on a variety of factors but the temperature at which, under 

 similar conditions, a precipitate is first visible is lowered by radiation 

 (4, 44, 54). That is, after radiation denaturation, the proteins are in 

 general more easily coagulated by heat. There are, however, special 

 cases where, after radiation, proteins no longer coagulate on heating 

 (5, 10, 29). 



Hydrogen Ion Concentration. — A number of investigators have noted 

 that there is a change in acidity after radiation. Mond (39, 40) and 

 Young (63) state that acid solutions become less acid and solutions on the 

 alkaline side of the isoelectric point become more acid. Stedman (54) 



