ANALOGS OF NICOTINAMIDE 489 



4(5)-3'-pyridylglyoxaline but the mechanism is unknown; it is quite pos- 

 sible that NADases other than from brain may not be so potently inhibited 

 by this substance since nicotine does not inhibit the beef spleen enzjTne. 

 Another surprisingly potent inhibitor is theobromine, which is bound to 

 rabbit erythrocyte NADase around 1 kcal/mole more tightly than the other 

 purines tested, the inhibition being competitive. Malkin and Denstedt 

 (1956) concluded from the inhibition data that NAD is attached to the 

 enzyme surface at the quaternary nitrogen and the pyrophosphate group. 

 It is rather strange that adenine is a reasonably effective inhibitor, whereas 

 adenosine or the adenine nucleotides are much weaker or completely with- 

 out action, since, if adenine were bound in the same position as it is when 

 part of the NAD molecule, one might expect ribose and phosphate groups 

 to augment the binding. Thus the inhibition by adenine and other purines 

 may involve interaction with the enzyme surface in a manner unrelated to 

 the normal binding of the purine component of NAD. This is further borne 

 out by the studies on multiple inhibition by Hofmann and Rapoport (1957) 

 (see accompanying tabulation), inasmuch as adenine does not add to the 

 inhibitions produced by inhibitors presumably interacting with enzyme 

 groups binding NAD. 



3-Acetylpyridine and the Formation of Analogs of NAD 



In a search for pjTidine derivatives which might have vitamin activity 

 against black tongue in dogs, Woolley et al. (1938) observed that 3-acetyl- 

 pyridine is not only ineffective but kills nicotinamide-deficient animals in 

 1 day, normal dogs being unaffected. 3-Acetylpyridine rapidly produces 

 signs of nicotinate deficiency in mice and at the LDjq (around 3 mg per day) 

 the animals succumb in 3 to 4 days (Woolley, 1945 b). The effects produced 

 are: rapid respiration, motor incoordination followed by complete paralysis, 

 emaciation, and inflamed skin and tongue. The mice can be completely 



