Binding of Riboflavin and Riboflavin Phosphate by the Proteins of Milk

The binding of riboflavin and riboflavin phosphate by the proteins of milk, particularly by a-and fl-casein, has been studied. Binding constants have been determined and, from these, thermodynamic quantities have been calculated. The binding is of a low order of magnitude with an unusually high temperature coefficient. The binding by the calcium easeinate-phosphate complex in milk is equivalent to the binding by its component protein molecules. Certain similarities between the binding by the caseins, and the binding by flavoprotein enzymes, have been noted. The data indicate strongly that phenoxyl residues constitute the loci of binding.