Butyrophilin of milk lipid globule membrane contains N-linked carbohydrates and cross-links with xanthine oxidase

1. N-glycanase, but not O-glycanase, released carbohydrates from butyrophilin of rat and cow milk lipid globule membranes. 2. 1-Deoxynojirimycin, and inhibitor of glucosidases I and II of the glycoprotein processing pathway, increased the amount or extent of glycosylation of butyrophilin in rat milk lipid globules. 3. Butyrophilin and xanthine oxidase of milk lipid globule membrane had a nearest neighbor relationship, as demonstrated through specific crosslinking of these proteins. 4. From these results it is suggested that butyrophilin has asparagine-linked oligosaccharides which bypass the processing apparatus of endoplasmic reticulum and Golgi apparatus. Butyrophilin may be responsible for anchoring xanthine oxidase to the inner (cytoplasmic) face of milk lipid globule membrane.