title: New thiocholine ester substrates for the assay of human serum cholinesterase.
abstract: BACKGROUND
  Several thiocholine alkanoyl esters were newly synthesized and explored as substrates for the assay of human serum cholinesterase after being subjected to the Ellman reaction (Arch Biochem Biophys 1958;74:443-50 and Arch Biochem Biophys 1959;82:70-7).
  
  
  METHODS
  We synthesized thiocholine ester iodides by the method of Renshow et al. (J Am Chem Soc 1938;60:1765-70). We examined solubility in H(2)O, substrate specificity serum for cholinesterase, (spontaneous) self-hydrolysis, storage stability, and reaction conditions for measurement of the activity of the enzyme.
  
  
  RESULTS
  Isobutyryl and cyclohexane-carboxyl esters showed the best efficiency for the specific and stable assay of human serum cholinesterase. Aqueous solubility of each was >10 mmol/L, and the reactivity with acetylcholinesterase was negligible. For isobutyryl and cyclohexane-carboxyl esters, respectively, spontaneous hydrolysis in the aqueous phase was approximately 1/25 and approximately 1/175 slower than the enzymatic hydrolysis, and assays with these substrates were linear to 1800 and 3000 U/L, respectively. The K(m) values of these acylthiocholines with human cholinesterase were almost equivalent (6.9 x 10(-3) mmol/L). The substrates were stable in aqueous solution and in the solid state as the iodides for at least 5 years at 5 degrees C.
  
  
  CONCLUSIONS
  The isobutyrate and cyclohexane-carboxylate of thiocholine are suitable for the specific assay of human serum cholinesterase.
authors.affiliation: International Reagents Co., Ltd., 4-3-2 Takatukadai, Nishiku, Kobe 651-2271, Japan. yama53@viola.ocn.ne.jp
authors.forename: M
authors.initials: M
authors.lastname: Yamada
authors.forename: Y
authors.initials: Y
authors.lastname: Marui
authors.forename: C
authors.initials: C
authors.lastname: Hayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Miki
authors.forename: S
authors.initials: S
authors.lastname: Takemura
mesh_terms: D002802:Cholinesterases / Q000097:blood / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007202:Indicators and Reagents; D007700:Kinetics; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013860:Thiocholine / Q000031:analogs & derivatives* / Q000138:chemical synthesis
chemical_list: D007202:Indicators and Reagents; D013860:Thiocholine; D002802:Cholinesterases