The Specificity of Milk Lipase. IV. Partition of the Lipase System in Milk

Abstract

All cow''s milk contains at least 2 different Upases: One, the "membrane lipase", which is irreversibly adsorbed onto the fat globules membrane material upon the cooling of freshly drawn milk; and the other the "plasma lipase", which remains in the plasma and is associated with caseinate fraction of milk. The "membrane lipase" was separated from the "plasma lipase" by washing (freeing from milk plasma) the cream obtained from precooled freshly drawn milk and isolating the membrane material of fat globules upon which the enzyme is adsorbed. The relative lipolytic activity of the plasma and the membrane material fractions of milk toward various esters was different. Both enzymes are present in all milks, but in certain milk-so called "naturally lipoly-tically active" or "spontaneous" milk usually from cows late in lactation[long dash]the "membrane lipase" is present in high concentration. The mode of lipolysis by each enzyme is discussed in relation to the control of hydrolytic rancidity in milk.