EFFECTS OF RADIATION ON ENZYMES 1159 



violet region of the spectrum, and that the process was that of a mono- 

 molecular change. The maximum light inactivation of pepsin occurs 

 at the pH of maximum activity, i.e., at 1.15, as found by Pincussen and 

 Uehara (67A'). At pH 1.93 and 2.28 there was no significant difference 

 between the activities of rayed and unrayed solutions. Calvin (11) 

 reported a decrease in the activity of pepsin and trypsin due to the effect 

 of radiations from a mercury-vapor lamp. Temperature and other factors 

 were controlled. Pace (1931) studied the effects of radiation from a 

 mercury-vapor arc upon solutions of trypsin and enterokinase which 

 had been previously partially inactivated by heat. Upon irradiation 

 by light around 2800 A, only further inactivation occurred; with visible 

 light only, there was no further effect upon the enzymes. Inactivation 

 was greater if the entire radiation of the quartz lamp was used. 



Northrop (61) irradiated dilute solutions of crystalline pepsin, buffered 

 at pH 4.65, in quartz tubes (the controls being glass tubes), using a 

 General Electric "Lab Arc" lamp as the light source, at a distance of 

 8.5 cm. The determination indicated a loss in activity of the pepsin, 

 accompanied by a corresponding decrease in the total protein nitrogen of 

 the solution, the latter suggesting the protein nature of the enzyme 

 preparation. The rate of inactivation was dependent upon pH, and was 

 a maximum at about pH 2.0. There was no change in activity or in 

 protein nitrogen in the controls, from which ultra-violet was largely 

 screened out. 



Gates (26) studied the absorption and destruction spectra of solutions 

 of Northrop's crystalline pepsin in the ultra-violet region. Petri dishes 

 covered with cellophane and with glass, respectively, served as exposure 

 and control vessels. The apparatus used included an air-cooled hori- 

 zontal quartz-mercury-vapor lamp, a large quartz monochromator, 

 thermopile, and galvanometer. The lamp was operated at 67 v. and 5.5 

 amp. Samples were exposed at 30 cm. at temperatures of 20° and 22°C. 

 At intervals, from 20 to 360 min., 5-ml. samples were removed for activity 

 and for absorption tests. Total absorption in the ultra-violet region 

 increased with the degree of inactivation, this increase being especially 

 marked between X2400 and 2750 A. The rate of inactivation was 

 sensitive to changes in pH, increasing with lower values, and apparently 

 bearing a one-quantum relationship to the energy flux. The destruction 

 spectrum of the enzyme was found to agree essentially with its absorption 

 spectrum and is similar to that of urease, as found by Kubowitz and 

 Haas (50). 



Tyrosinase activity in two substrates, according to experiments of 

 Pincussen and Hammerich (67r), was easily destroyed by radiations from 

 a quartz-mercury-vapor arc. However, in the irradiation of Dolichos 

 tyrosinase, described by Narayanamurti and Ramaswami (59), irradiation 

 accelerated activity; but about one-half of this increased activity was 



