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Clinical Chemistry 17: 183-191, 1971;
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Clinical Chemistry, Vol 17, 183-191, Copyright © 1971 by the American Association for Clinical Chemistry

Serum Cholinesterase Variants: Examination of Several Differential Inhibitors, Salts, and Buffers Used to Measure Enzyme Activity

Philip J. Garry 1

1 Department of Pediatrics, College of Medicine, The Ohio State University and Children’s Hospital Research Foundation, 561 S. 17th St., Columbus, Ohio 43205.

Dibucaine, used as a differential inhibitor with acetyl-, propionyl-, and butyrylthiocholine 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 (NaCl, KCl, MgCl2, CaCl2, and BaCl2) activated the "usual" and inhibited 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 0.226 mmol/liter, respectively, with butyrylthiocholine as substrate.


Key Words: butyryithiocholine substrate • enzyme kinetics • distinction of "usual," heterozygous, and "atypical" forms of the enzyme

Submitted on October 19, 1970
Accepted on January 6, 1971




The following articles in journals at HighWire Press have cited this article:


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 ScienceHome page
A. H. Lubin, P. J. Garry, and G. M. Owen
Sex and Population Differences in the Incidence of a Plasma Cholinesterase Variant
Science, July 9, 1971; 173(3992): 161 - 164.
[Abstract] [PDF]


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Copyright © 1971 by the American Association for Clinical Chemistry.