2. ANALOGS OF ENZYME REACTION COMPONENTS 



tent inhibition produced by 2-amino-4-hydroxy-6-pteridyl aldehyde, a 

 photolytic product of folate, led to the conclusion, subsequently verified, 

 that this was the contaminant (Kalckar et al., 1948; Lowry et al., 1949 a, 

 b). For convenience we shall follow Hofstee (1949) in designating 2-amino- 

 4-hydroxypteridine as pterin and the inhibitor thus as pterin-6 -aldehyde* 

 Pterin and many of its substituted derivatives are oxidized to varying 

 degrees by xanthine oxidase while other derivatives are only inhibitory. 



* This substance has been variably called 2-amino-4-hydroxy-6-pteridyl aldehyde, 

 2-amino-4-hydroxy-6-formylpteridine, 6-formylpteridine, pteridylaldehyde, 2-amino- 

 4-hydroxy-6-pteridine carboxaldehyde, and 2-amino-4-hydroxy-6-formylpterine, in 

 most cases without either justification or accuracy. 



