Studies on the properties of cow's-milk tributyrinases and their interaction with milk proteins

Abstract

1. The tributyrinases in milk are mainly associated with casein micelles. Dilution or addition of sodium chloride increases the enzyme activity, probably by dissociating the micelle-tributyrinase complexes. 2. Tributyrinase activities of milks activated by dilution and sodium chloride addition were in the range 0.2-1.7muequiv. of acid liberated/ml. of milk/min. from tributyrin emulsion at pH8.5 and 25 degrees . The enzymes have a bivalent-cation requirement for full activity and are rather unstable when separated from casein. 3. Ultracentrifugation of skim milks containing sodium chloride (0.75m) gave preparations low in casein but containing about 70% of the milk tributyrinases. The tributyrinases in such preparations appear to be bound in complexes of molecular weight about 350000. Dilution may result in dissociation to give the free enzymes. 4. Pancreatic lipase also formed complexes with casein micelles, but wheat-germ esterase, xanthine oxidase, milk alkaline phosphatase and other enzymes did not.

Possible Role of Sialic Acid in Bovine Mastitis with particular reference to milk electrical conductivity

“…The milk sialic acid concentrations in healthy cows (51 pg/ml) were somewhat lower than reported previously by MARIER et al (1963), DOWNEY andANDERS (1966) andTRUE et al (1969) who obtained mean values between 87 and 100 pg/ml. Much of the difference may be explained by the more strict criteria used by us to obtain reliably healthy animals.…”

Indigenous enzymes in milk: Overview and historical aspects—Part 1

“…It seems likely that these multiple forms of lipase were due to the self-association of lipase or to association with other milk proteins (see Shahani & Chandan, 1965). At least 90% of the lipase in milk is associated with the CN micelles (Gaffney, Harper, & Gould, 1962, 1966, but it can be dissociated from the micelles by treatment with 1 M NaCl (Downey & Andrews, 1966), dimethylformamide (Fox, Yaguchi, & Tarassuk, 1967) or heparin (Hoynes & Downey, 1973).…”

Effect of the fat globule membrane on in vitro digestion of milk fat globules with pancreatic lipase

“…Pancreatic lipase may have higher affinity for the micellar casein surface of fat globules, leading to more lipase binding with the interface of fat globules. It has been reported that virtually all intrinsic milk lipoprotein lipase is associated with casein, with about 70% is bound to micellar casein and the remainder existing in the form of soluble caseineenzyme complexes in the milk serum (Anderson, 1982;Downey & Andrews, 1966). This may be attributed to the promotion of lipolysis in milk that is agitated or homogenized, because of disruption of the MFGM and adsorption of caseins on to the surface of fat globules (Cartier & Chilliard, 1989), such that the casein brings more lipase to the interface of the fat globules.…”