Abstract
1) The decomposition of procaine by human plasma is markedly inhibited by cholinesterase (ChE) inhibitors. 2) Mutual inhibition is observed between procaine and acetylcholine. 3) The existence of both procaine esterase (PrE) and ChE is closely related to α- and β-globulin fractions. 4) The activity of PrE is inhibited by divalent cations, such as Mn++ or Mg++, but that of ChE is accelerated by them. 5) In various mammalian plasmas no analogous relationship is observed between the order of PrE activity and ChE activity. 6) PrE and ChE resemble to each other in various points, although they are different in some respects.
