cAMP stability

[David LaPorte Biochem]

jmello1 at umbc.edu (mellott james ( bs bioc)) writes:
>	In my biochemistry class , we're talking about glycolysis , TCA , etc.,
>and one of the topics is the regulation of glycogen through a cAMP pathway . It
>is my understanding that a high concentration of cAMP is needed for the 
>continuous activation of Protein kinase , and to inactivate the kinase , the 
>concentration of cAMP is lowered through the activity of a phosphodiesterase . 
>I recall hearing that caffeine stabilizes the concentration of cAMP in such a
>pathway , and I was wondering , since caffeine and adenine have similar 
>structures , if caffeine acts as a competitive inhibitor with cAMP for the 
>phosphodiesterase . 

Caffeine, theophiline and related compounds are, indeed, inhibitors of 
phosphodiesterase.  As I recall, however, that is not their biological
site of action.  The concentrations required to produce a physiological
effect are too low to inhibit PDE. 

Dave LaPorte
U. of Minn.
david-l at microbe.med.umn.edu