What hydrolyses aspirin within the digestive tract and blood stream?
Acetylsalicylate deacetylase is the enzyme responsible for this reaction.


  Precisely, the present investigation reveals that the hydrolysis of aspirin in liver, kidney and probably other tissues of
  rats is catalyzed by two highly substrate specific microsomal
  esterases, ASA esterase I and II active at acidic and slightly
  alkaline pH, respectively. The findings that ASA esterases have
  distinct organ distribution pattern and display responses to
  various inhibitors/activators that are different in many respects
  from those exhibited by cholinesterase and nonspecific carboxylesterase suggest that the latter esterases probably do not play
  a significant role in the hydrolysis of aspirin.
  
  From:
  Ali B, Kaur S (1983) Mammalian tissue acetylsalicylic acid esterase(s): identification, distribution and discrimination from other esterases. J Pharmacol Exp Ther,226,589-594