Gel filtration profile of folate binding proteins in Triton X-100 solubilized human raw milk

Solubilization of human raw milk with Triton X-100 gave rise to a two-fold increase in maximum [3H] folate binding as determined in equilibrium dialysis experiments (pH 7.4, 37 degrees C). Gel filtration studies on Triton X-100 solubilized human milk revealed three distinct peaks of protein-bound [3H] folate, Mr approximately 25 000 (38%), Mr greater than or equal to 130 000 (15%) and Mr approximately 100 000 (47%). The first peak was identical to the folate binder previously isolated from human whey, while the second peak most likely represented a particulate membrane-bound form of that binder. The third so far undescribed peak (Mr greater than or equal to 100 000) seemed to contain hydrophobic residues, and might be encapsulated in Triton X-100 micelles. This peak may represent a Triton X-100 solubilized split product of the large particulate binder.