Isolation of Lactoperoxidase of 89,000 Daltons and a Globulin of 81,000 Daltons from Milk Acid Whey

Two unidentified minor proteins of milk, P3AA and P3W, known in cottage cheese whey by SDS electrophoretograms as the 94,000-dalton and 84,000-dalton bands, were isolated from acid whey by gel filtration on Sephacryl S-200 and by hydrophobic interation chromatography on Butyl Toyopearl 650M. Each protein showed an electrophoretically homogeneous single band on SDS-PAGE. P3AA had an albumin character with a yellow color and a large Soret band at 412 nm, and this protein was confirmed to be lactoperoxidase. P3W was assumed to be a type of globulin because of its precipitation in saturated sodium sulfate and 50% saturated ammonium sulfate; however, it did not coagulate when dialysed against deionized water. Concentration of P3AA was estimated at 28 mg/L of acid whey. P3W was estimated at 130 mg/L. Molecular weight of P3AA is assumed to be 89,000 rather than 94,000 daltons, and P3W is 81,000 rather than 84,000.