310 BIOLOGICAL EFFECTS OF RADIATION 



ULTRA-VIOLET RADIATION 



Denaturation. — The effect of radiation on proteins has been reviewed 

 by Spiegel- Adolf (49, 50). The most striking and important change 

 produced in all proteins, whether globulins or albumins, whether posi- 

 tively or negatively charged, is a change in solubility or denaturation. 

 Proteins are denatured by the wave-lengths of ultra-violet radiation 



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which they absorb {i.e., X shorter than 3000 A). Salt-free albumin 

 exposed to ultra-violet radiation shorter than 3000 A shows no coagulation 

 except near the isoelectric point, but after radiation it flocculates if 

 brought to the isoelectric point or on dialysis (10). Pseudoglobulin 

 becomes less soluble and precipitates at the isoelectric point like a 

 euglobulin. Euglobulin, after radiation, has a wider zone of flocculation 

 at the isoelectric point. All three types, after radiation, are more easily 

 thrown out of solution by any precipitating agent, such as salts or alcohol. 

 Denaturation, or loss of affinity for water, occurs therefore without 

 exception when proteins are exposed to ultra-violet radiation. 



Radiation denaturation has not been studied in the exact quantitative 

 way that heat denaturation was studied by Chick and Martin (7, 8). 

 Results so far indicate that radiation denaturation and heat denaturation, 

 though resulting in the same solubility changes (10), are brought about 

 by a different type of physicochemical change. Under certain conditions 

 (5, 10) (at pH > 5.4 and 0°C.) albumin after radiation will no longer 

 precipitate on boiling, although it precipitates like a globulin on one-half 

 saturation with ammonium sulphate. Spiegel-Adolf (50, 53) states that 

 the increase in absorption after radiation, noted in detail below, does not 

 occur after heat denaturation except for a slight effect at wave-lengths 



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shorter than 2750 A. Viscosity and surface-tension changes have not 

 been compared after heat denaturation and radiation denaturation in 

 many proteins but show differences in the case of egg albumin (10). 

 The reversibility of heat coagulation under certain conditions has been 

 established and it is stated by Spiegel-Adolf (47, 50) that light denatura- 

 tion is not reversible. Heat denaturation without flocculation does not 

 change the osmotic pressure of proteins (30), but no experiments have 

 been carried out on the osmotic pressure of radiated proteins and it is 

 not known if radiation denaturation is a unimolecular reaction like heat 

 denaturation (7, 8) or not. Heat denaturation occurs only in the 

 presence of water (7, 8), but Stedman (54) states that proteins are 

 denatured when radiated dry, an observation confirmed by unpublished 

 observations of the author on dried, crystalline egg albumin. Further 

 work is necessary before definite conclusions can be drawn, but it seems, 

 from the scattered results so far reported, that the physicochemical 

 changes resulting in heat denaturation and radiation denaturation aFe 

 different. (See footnote*, page 319.) 



