Lipoprotein lipase in "Christiesomes" from goats' milk: a membrane-bound enzyme [proceedings].

The freshly secreted milk of goats has been shown (McCarthy & Patton, 1964; Christie, 1974) to catalyse a number of enzymic reactions of lipogenesis. Further experiments showed these activities to be localized in closed vesicular structures present in the milk. Their properties indicate that they originate from the mammary epithelium (Christie & Wooding, 1975); they are, effectively, anucleate mammary epithelial ‘minicells’, and have been aptly and conveniently named ‘Christiesomes’ (Wooding et al., 1977). The use of this term is continued in the present report, whose purpose is to describe and characterize a lipoprotein lipase activity (EC 3.1.1.34) associated with Christiesomes. A comparison of some of the properties of lipoprotein lipase in skimmed milk and Christiesomes prepared from freshly secreted goats’ milk is summarized in Table 1. With the exception of the anomalous response of skimmed milk lipoprotein lipase to assay in the presence of protamine sulphate, these results give no reason to conclude that the Christiesomal lipoprotein lipase is different from the total skimmed-milk activity. Quantitative estimates of Christiesome concentration in skimmed milk, together with measurements of rates of lipoprotein lipase activity in isolated Christiesomes, indicate that Christiesomes account for less than 10 % of the lipoprotein lipase activity in skimmed milk: the remainder is almost exclusively (as in cows’ milk; see e.g. Downey & Murphy, 1970) in the casein micellar fraction.