Esterases in the milk and blood plasma of swine. II. Activities at different stages during the lactation and suckling periods, and plasma arylesterase as a gene-controlled enzyme.

swine, and in low or medium concentration in that of others. 4. The sensitivity of the milk and plasma esterases to various inhibitors has been examined. 5. 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. 6. The milk electrophoresis pattem is characterized by one peak of maximum butyrylcholinesterase activity. At pH 8-4, the enzyme moves more slowly than all major milk-protein components. 7. In addition to the slow-moving esterase fraction of mature milk, a second faster-moving fraction of high esterase activity is characteristic of the electrophoresis pattern of colostrum. The properties of the esterase present in the two fractions are similar. 8. Arylesterase of plasma moves together with the albumin components. Plasma butyrylcholinesterase is concentrated in two separated fractions, one moving together with arylesterase, the other having the same mobility as the faster-moving enzyme of colostrum. 9. The implications of these observations are discussed.