@article {Hofstee299, author = {B. H. J. Hofstee}, title = {MECHANISM OF ACTION OF BIVALENT METAL IONS AND OF PHENOTHIAZINE DERIVATIVES ON SERUM CHOLINESTERASE}, volume = {128}, number = {3}, pages = {299--306}, year = {1960}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {The kinetics of metal activation of the hydrolysis of the anions of n-fatty acid esters of m-hydroxybenzoic acid by serum cholinesterase indicates that the metal facilitates the approach of these substrates to the enzyme. The combination ratio of enzyme and bivalent metal (Ca++, Mg++, Mn++) is not 1:1 as would be the case if "bridge" formation were involved. The inhibition of the enzyme by phenothiazines, e.g., Thorazine, Diparcol and methylene blue, occurs through a mechanism that is primarily noncompetitive with respect to the substrate but that is competitive with the metal. The inhibitors enter into rapid equilibrium with the enzyme, even in the presence of substrate. These results have been tentatively interpreted on the basis of the presence of an auxiliary group on the enzyme molecule in addition to the active group proper ("esteratic" site). The specific structure around the auxiliary group is essential for activity and has high affinity for phenothiazines. It carries a nonessential negative charge that repels anionic substrates and is neutralized by certain bivalent metals. Ionic forces are negligible in the interaction with phenothiazines, which even as free (uncharged) bases have Ki values as low as 10-7 M, e.g., Diparcol.}, issn = {0022-3565}, URL = {https://jpet.aspetjournals.org/content/128/3/299}, eprint = {https://jpet.aspetjournals.org/content/128/3/299.full.pdf}, journal = {Journal of Pharmacology and Experimental Therapeutics} }