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Proteose-Peptone Fraction of Bovine Milk: Lacteal Serum Components 5 and 8—Casein-Associated Glycoproteins¹

Department of Food Science, Michigan State University, East Lansing 48823

ABSTRACT

Lacteal serum Components 5 and 8 were isolated from both heated and unheated skimmilk. At pH 8.6 Component 5 migrated as a double zone in starch-urea-gels (discontinuous buffer) and as a single zone in poly aery lamide gels (continuous buffer). Component 8 migrated in the ion front on starch gels but resolved into two principal zones in the polyacrylamide gel system, designated as 8-f ast and 8-slow in ascending order of relative mobility. Components 8-fast and 8-slow were fractionated by gel-permeation chromatography on Bio-Gel P-10 polyacrylamide beads.

Component 5 is characterized by its high proline («=* 10.5%) and relatively low carbohydrate contents (=«1.5%). Components 8-fast and 8-slow contain relatively high concentrations of total phosphorus («=< 7.4 and 5.5% as H₂P0₃) and intermediate amounts of carbohydrate (« 2.07 and 9.0%). All three components are void of cysteine and cystine and contain only low concentrations of methionine.

In veronal buffer at pH 8.6, r/2 = 0.1, a sedimentation coefficient (S°2o,w) of 1.22 and a molecular weight (_w) of >=» 14,300 were observed for Component 5. Similar parameters for Components 8-fast and 8-slow were Sdegrees = °2o,w = 4,100 and 9,900. An isoelectric pH of 3.3 is reported for Component 8-fast and partial specific volumes () of 0.736, 0.700, and 0.719 (cc/g) for Component 5, 8-slow, and 8-fast were calculated from composition data.

¹ Published as Journal article no. 5011 from the Michigan Agricultural Experiment Station.

² Present address: Ralston-Purina Corp., St. Louis, Missouri.