Amino-terminal sequencing of the ovine milk fat globule membrane protein butyrophilin

Butyrophilin, a transmembrane protein of the milk fat globule membrane, was identified in cows' and ewes' milk by amino acid N-terminal sequencing. The N-terminal part of ovine butyrophilin was identical to that of the human protein. A butyrophilin-type protein with an M-r of 62 000 was also found in equimolar proportions with butyrophilin in ovine milk. This smaller M-r form was probably generated by plasmin-mediated hydrolysis during or following lactation in the epithelial cells of the mammary gland and corresponded to a smaller M-r form of butyrophilin lacking the C-terminal region. (C) Inra/Elsevier, Paris.