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The Specificity of Milk Lipase. II. Kinetics, and Relative Lipolytic Activity in Different Milks^{1, 2,}

The Department of Dairy Industry, University of California, Davis

ABSTRACT

The values obtained for maximum velocity (Vm) for the lipolytic activity in milk toward milk fat, Tween-20, and methyl butyrate were 1.6, 2.4, and 2.1 (units per 100 ml.), respectively, and the values for the Michaelis-Menten constant were 6.3%, 0.81%, and 0.54 M, respectively. The values for the activation energy in the range of 30 to 37° C. for the milk fat, Tween-20, and methyl butyrate hydrolyses were calculated to be 6,200, 14,500, and 12,500 calories, respectively. The kinetic data were considered in terms of a multiple lipase system in milk. The limitations of this approach were emphasized.

The variation in the relative lipolytic activity obtained in different milks towards different substrates is considered to be preliminary evidence for the presence of multiple lipolytic enzymes in milk.

¹ The data are part of a thesis presented to the Graduate School of the University of California by the senior author in partial fulfillment of the requirements for the degree of Doctor of Philosophy, January, 1956.

² This study was supported in part by funds from the California Dairy Industry Advisory Board.

³ Present address: Northern Utilization Research Branch, USDA, Peoria, Ill.