Lactose Synthetase

• Published in: European journal of biochemistry Vol. 64; no. 1; pp. 233 - 242
• Main Authors: IVTT, Raymond J., ROSEMEYER, Michael A.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.04.1976
• ISSN: 0014-2956; 1432-1033
• DOI: 10.1111/j.1432-1033.1976.tb10292.x

Galactosyl transferase and α‐lactalbumin were concurrently, isolated from bovine milk. The galactosyl transferase had an S20,W of 3.0 S and D20,W of 60 μm2/s. It exists as a monomer of 46000 molecular weight, as determined by sedimentation equilibrium and dodecylsulphatepolyacrylamide electrophoresis. Aggregation of the enzyme was promoted by N‐acetylglucosamine. Sedimentation velocity experiments show an association between galactosyl transferase and α‐lactalbumin in the presence of N‐acetylglucosamine. In contrast, UDP‐galactose, UDP or lactose do not promote protein‐protein association. A complex between galactosyl transferase and α‐lactalbumin was isolated by gel filtration in the presence of excess α‐lactalbumin and either N‐acetylglucosamine or glucose. The complex was stable over arrange of concentrations of these components. The complex is a discrete homogeneous entity with a molecular weight of 60000, corresponding to one molecule of galactosyl transferase and one molecule of α‐lactalbumin. The estimated association constants for the ternary complexes of the two proteins and either of the sugars, suggest that α‐lactalbumin enhances equally the binding of N‐acetylglucosamine or glucose to the galactosyl transferase.