Evidence for the presence of several lipases in cow's milk

Abstract

Skim milks containing sodium chloride (0.75m) were centrifuged at 80000g for 2hr. and portions of the supernatants were submitted to gel filtration on columns of Sephadex G-200. Enzymes in the effluent fractions were assayed titrimetrically for their hydrolytic activities towards tributyrin, triolein and milk-fat emulsions, and triacetin solution. Summation of the measurements gave ratios of activities towards the various substrates similar to those of the original skim milks. Although only partial separation was obtained, five enzymes appeared to be present. They showed some differences in substrate specificity, but all appeared to be lipases in that they hydrolysed the emulsified substrates more rapidly than the dissolved triacetin.

Lipoprotein lipase and lipolysis in milk

“…Despite early research suggesting otherwise (Downey & Andrews, 1969), it is now accepted that only one lipolytic enzyme, lipoprotein lipase (LPL), accounts for most, if not all, of the lipolytic activity in bovine milk (Olivecrona, 1980;Olivecrona, Vilaro, & Olivecrona, 2003). This is not the case for human milk, which contains a bile-saltstimulated lipase in addition to LPL.…”

Triglyceride lipase activity in subcellular fractions from beef heart

“…Relative TGL-activity* * Average of 5 experiments with standard error of the mean. ** Supernatant after centrifuation at 80 000 g for 2 hr of raw skimmilk made 0.75 M with respect to NaCI [16]. experiments) that only a very rough estimate of microsomal contamination of the mitochondrial fraction in order of 20-50% could be obtained.…”

“…** Supernatant after centrifuation at 80 000 g for 2 hr of raw skimmilk made 0.75 M with respect to NaCI [16].…”

Association of lipases with micellar and soluble casein complexes

“…It has been well documented that the lipase activity in milk is mainly associated with the casein (Harper, Gould & Badami, 1956;Tarassuk & Frankel, 1957;Saito, 1963;Gaffney, Harper & Gould, 1962). Aside from the hypothesis (Downey & Andrews, 19656) that lipase will bind only to micellar casein, the nature of the binding has not been investigated nor has it been unequivocally established whether the lipase activity in milk is specifically associated with an individual casein. Skean & Overcast (1961) showed by means of continuous paper electrophoresis that lipase activity is associated with the a-casein fraction.…”

“…In an attempt to resolve these anomalous results an alternative approach was explored in the present investigation. Pancreatic lipase, which appears to interact with casein micelles in a manner similar to milk lipases (Downey & Andrews, 19656), was added to milk and to colloidal phosphate-free milk, and the resultant lipasecasein complexes investigated by gel-filtration. The use of a lipase preparation containing no milk proteins and in which the enzyme is known to exist as a monomer (Downey & Andrews, 1965 a) enabled us to study the association of free lipase with casein micelles and complexes.…”