114 



H. Laser 



experiments to be described was a flavoprotein, namely notatin 

 (glucose oxidase) (Keilin and Hartree, 1948). By means of a 

 manometric micro-method for determining the initial rates of 

 glucose oxidation by small amounts of enzyme ( < 1 (jig.) in- 

 activation of the enzyme of the order of 10-20 per cent could 

 be reproducibly detected with accuracy. Table I, dealing with 



Table I 



the application of 38 kr X-rays reveals the, at first sight sur- 

 prising, result of a reversal of the oxygen effect, the enzymic 

 activity being practically completely inhibited by irradiation 

 in nitrogen but only slightly (15 per cent) depressed if oxygen 

 is present. However, the presence of glucose, the specific sub- 

 strate, during irradiation in air brought about a strong 

 inhibition (50 per cent) while the presence of glucose during ir- 

 radiation in nitrogen protected, lessening the inactivation from 

 100 per cent to 15 per cent. Catalase, in catalytic amounts, did 

 not alleviate the inhibition which glucose caused during irradi- 

 ation in air, i.e., the enzyme had not been partially inactivated 

 either by enzymically or radiochemically produced HgOg. 

 The inactivation of notatin on irradiation in air was observed 

 only in the presence of its specific substrate. A number of 

 other sugars, which are not oxidized by the enzyme, caused no 

 inactivation in air but exerted a high degree of protection 

 during irradiation in nitrogen. Similarly, added protein 

 (albumin), which greatly protected against irradiation in 



