Esterases in the milk and blood plasma of swine. 1. Substrate specificity and electrophoresis studies

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Abstract
Sow''s milk contains in high concentration a butyrylcholinesterase with a substrate-specificity pattern differing from all other cholin-esterases. This enzyme hydrolyzes phenyl acetate at a rate which is only slightly lower than that of butyrylcholine. No other esterase is present in important amounts in sow''s milk. Swine plasma contains the same butyryl-cholinesterase although in 20-25 times lower concentration. An acetylarylesterase (aromatic esterase) is present in high concentration in the plasma of some swine, and in low or medium concentration in that of others. The sensitivity of the milk and plasma esterases to various inhibitors has been examined. Electrophoresis in cellulose columns has been performed with milk, colostrum and blood serum of swine, and also with mixtures of separated and crude enzyme preparations. The milk electrophoresis pattern is characterized by one peak of maximum butyrylcholinesterase activity. At pH 8. 4, the enzyme moves more slowly than all major milk-protein components. In addition to the slow-moving esterase fraction of mature milk, a second faster-moving fraction of high esterase activity is characteristic of the electro-phoresis pattern of colostrum. The properties of the esterase present in the 2 fractions are similar. Arylesterase of plasma moves together with the albumin components. Plasma butyrylcholinesterase is concen-trated in 2 separated fractions, one moving together with arylesterase, the other having the same mobility as the faster-moving enzyme of colostrum. The implications of these observations are discussed.