During exercise when the ATP reservoir is low (ADP>ATP), the purine nucleotide cycle produces ammonia (NH) when it converts AMP into IMP. (With the exception of AMP deaminase deficiency, where ammonia is produced during exercise when adenosine, from AMP, is converted into inosine). During rest (ADP<ATP), ammonia is produced from the conversion of adenosine into inosine by adenosine deaminase. 
:AMP + HO + H → IMP + NH (catalyzed by AMP deaminase in skeletal muscle)
:Adenosine + HO → Inosine + NH (catalyzed by adenosine deaminase in skeletal muscle, blood, liver)
Ammonia is toxic, disrupts cell function, and permeates cell membranes. Ammonia becomes ammonium (NH) depending on the pH of the cell or plasma. Ammonium is relatively non-toxic and does not readily permeate cell membranes.  + H ⇌ NH) diffuses into the blood, circulating to the liver to be neutralized by the urea cycle. (N.b. urea is not the same as uric acid, though both are end products of the purine nucleotide cycle, from ammonia and nucleotides respectively.) When the skeletal muscles are at rest (ADP) combines with glutamate to produce glutamine, which is an energy-consuming step, and the glutamine enters the blood. + ATP → Glutamine + ADP + P (catalyzed by glutamine synthetase in resting skeletal muscle) molecules neutralise the organic acids (lactic acid and ketone bodies) produced in the muscles.O → Glutamate + NH (catalyzed by glutaminase in the kidneys)</blockquote>