Isolation of a new ligand-carrying casein fragment from bovine mammary gland microsomes

Whilst looking for components involved in retinol metabolism in secreting mammary gland cells, a 12 kDa protein was isolated. This protein had bound a ligand with characteristics of retinol. N-Terminal sequencing and amino acid analysis showed that this protein is highly homologous with an ?-s1-casein fragment. No ligand was found for ?-lactoglobulin, previously thought to be involved in retinol metabolism.