SerumCholinesteraseVariants:Examinationof SeveralDifferentialInhibitors,Salts,and

Dibucaine, used as a differential inhibitor with acetyl-, propionyl-, and butyr. ylthiocholine as substrate, clearly identified the “usual ” and “atypical” serum cholinesterases. Succinylcholine was also used successfully as a differential inhibitor with butyrylthiocholine as substrate. Sodium fluoride, used as a differential inhibitor, gave conflicting results, depending on whether Tris or phosphate buffer was used in the assay. Mono and divalent cations (NaCI, KCI, MgCI,, CaCI,, and BaCI,) activated the “usual ” and jn. hibited the “atypical ” enzyme at low concentrations. The “usual ” enzyme had the same activity in 0.05 mol of Tris or phosphate buffer per liter, while the heterozygous and “atypical ” enzymes showed 12 and 42 % inhibition, respectively, when assayed in the phosphate buffer. Kinetic studies showed the phosphate acted as a competitive inhibitor of “atypical ” enzyme. Km values, determined for “usual ” and “atypical ” enzymes, were 0.057 and 0.226mmol/Iiter, respectively, with butyrylthiocholine as substrate. Additional Keyphrases butyryithiocholine substrate #{149} enzyme kinetic