COMPARTMENTALIZATION OF FUCOSYL-TRANSFERASE AND ALPHA-L-FUCOSIDASE INHUMAN-MILK

Several pathogenic agents of pediatric gastroenteritis are inhibited b y fucosylated oligosaccharides of human milk. Biosynthesis and degrada tion of fucosyloligosaccharides is controlled by fucosyltransferase an d ru alpha-L-fucosidase. The activity of these enzymes varies reciproc ally over the course of lactation. We hypothesized that differences in the specific organization of these enzymes in compartments of human m ilk might contribute to such differences in activity. Therefore, the d istribution of these enzymes in various compartments of human milk was investigated. After ultracentrifugation at 120,000g for 2h, the fucos yltransferase activity distributes evenly between the supernatant and the membranous pellet. Ultracentrifugation at 180,000g for 17 h furthe r fractionated the milk into a clear supernatant, a fluff layer from t he supernatant, and a pellet. The fluff was visualized by electron mic roscopy. The distribution of fucosyltransferase activity in colostrum was compared with that of mature milk from the same donor, In mature m ilk from Day 30 of lactation, most fucosyltransferase activity was in the membranous buff fraction, while in colostrum from Day 5 of lactati on, most of the fucosyltransferase activity was in the supernatant. In contrast to fucosyltransferase, fucosidase activity was found only in the soluble milk fraction; upon prolonged ultracentrifugation, most o f this was membrane associated, The nature of human milk fucosidase wa s studied. This enzyme is glycosylated and exhibits several characteri stics common to other fucosidases. Under the conditions found is human milk, it exhibits almost full activity, The variation in compartmenta lization of fucosyltransferase activity during lactation may reflect v ariations in metabolism of the fucosyloligosaccharides of human milk t hat protect against disease. (C) 1996 Academic Press, Inc.