Dissociation of the Soluble Glycoprotein of Bovine Milk Fat Globule Membrane by Sodium Dodecyl Sulfate

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Abstract
Structural polypeptides of a soluble glycoprotein isolated from the delipidized bovine milk fat globule membrane were investigated by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The soluble glycoprotein dissociated by SDS was found to be composed of at least eight polypeptides on SDS-polyacrylamide gel electrophoresis. Of the eight, seven were detected by periodic acid-Schiff staining for carbohydrate (PAS-I to VII) and three by coomassie blue staining for protein (CB-I to III). PAS-IV and V had the same mobilities as CB-I and II, respectively. PAS-I, II, III and VI, which were not detected by protein staining, were shown to be glycopeptides by proteolysis experiments. The apparent molecular weights were estimated to be ranging from 88,000 to 10,000 daltons on SDS-polyacrylamide gel electrophoresis with an increase in gel concentration. The electrophoretic patterns and apparent molecular weights of these constituent polypeptides of the soluble glycoprotein were evidently different from those of the insoluble apoprotein fractions, which were dissociated into at least 13 coomassie blue positive bands and 7 periodic acid-Schiff positive bands.