Purification of Two Unusual Serum Cholinesterase Variants (Ch(I)^D and Ch(I)^F) and Comparison of their Properties with those of Normals

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Abstract
(1) Two rare genetic variants (Ch(I)^D and Ch(I)^F) of human cholinesterase were purified by a three-step technique. The atypical cholinesterase (Ch(I)^D) was purified by a factor of 2,230 with a recovery of 11 % of the original activity. The fluorideresistant (Ch(I)^F) variant was purified 5,000-fold with a recovery of 17%. The poorer recovery is attributed to lesser stability of the unusual variants. The atypical enzyme was less stable than the normal (Ch(I)^U) in 20 mmol/l acetate buffer, pH 4.0. (2) The catalytic, physical, and immunological properties of the atypical and fluorideresistant enzymes were compared with those of the normal (Ch(I)^U). The apparent catalytical properties appeared to be unchanged by the purification procedure. The specific activity of the fluoride-resistant enzyme was about 20% of the normal and that of the atypical enzyme was about 6% for all three substrates studied. The significance of the much lower activities of the atypical variant is discussed. All three variants were equally affected by sialidase. (3) The isoelectric points were estimated to be 3.99 for the normal, 4.20 for atypical, and 3.70 for the fluoride-resistant cholinesterase. The three variants appeared to be immunologically similar and have similar molecular weights. (4) The chromatographic mobilities of the enzyme variants on a DEAE-cellulose column at pH 4.0 in 20 mmol/l acetate buffer were compared. A physical separation of Ch(I)^U and Ch(I)^F variants present in plasma from an individual heterozygous for Ch(I)^U Ch(I)^F were obtained by DEAE-cellulose chromatography.