The arylesterases of human serum

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Abstract
Preparative electrophoresis on cellulose columns at pH 8.0 revealed three distinct forms of arylesterase activity. The leading esterase zone migrated ahead of albumin on a cellulose electrophoresis column but behind the albumin on starch-gel electrophoresis. The second arylesterase zone was associated with albumin, and the third with cholinesterase. The pre-albumin and cholinesterase fractions each contained more than one arylesterase but the albumin fraction contained only one arylesterase. The pH optima of the pre-albumin-fraction and albumin-fraction arylesterases were both 7.9, whereas the optimum pH for the hydrolysis of both phenyl acetate and acetylcholine by cholinesterase was 8.5. In experiments with phenyl esters, the preferred acyl group for the c pre-albumin-fraction arylesterase was acetyl, the albumin-fraction enzyme showed no marked specificity and that for cholinesterase was butyryl. The pre-albumin-fraction esterase, unlike the other two, was sensitive to reagents for thiol groups and required Ca2+ ions for activation.