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Journal of Dairy Science Vol. 77 No. 4 930-939
© 1994 by American Dairy Science Association ®
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Enterotoxin-Binding Glycoproteins in a Proteose-Peptone Fraction of Heated Bovine Milk

Kan Shida 1, Kotaro Takamizawa 1, Masato Nagaoka 1, Akira Kushiro 1, Toshiaki Osawa 1, and Takao Tsujl 2

1 Yakult Central Institute for Microbiological Research, 1796 Yaho, Kunitachi, Tokyo 186, Japan
2 Department of Microbiology, Fujita Health University School of Medicine, Toyoake, Aichi 470-11, Japan

The binding of Escherichia coli heat-labile enterotoxin to caseins, whey proteins, milk fat globule membrane, and proteose-peptone fraction from bovine milk was studied by using the Western blot technique. Two toxin-binding glycoproteins, ppl6k and pp20k, with molecular weights of 15,500 and 20,000, respectively, were detected only in a proteose-peptone fraction. These glycoproteins were partially purified by ammonium sulfate precipitation and Toyopearl HW 55 gel filtration chromatography. The binding ability to the toxin was destroyed by periodate treatment or ß-galactosidase treatment, indicating that a carbohydrate moiety, particularly a terminal galactosyl residue, was essential for the binding of the toxin. In contrast, the binding ability was not changed by mild acid treatment, and these glycoproteins did not bind cholera toxin, which can bind to ganglioside GM1, suggesting that the carbohydrate structure of the glycoproteins is different from that of GM1. The N-terminal amino acid sequence and immunoblot analysis indicated that the protein moieties of ppl6k and pp20k are identical to alphalactalbumin and ß-lactoglobulin, respectively. These toxin-binding glycoproteins were not detected in whey proteins isolated from unheated skim milk, suggesting that they are newly generated during heat treatment of skim milk before the preparation of a proteosepeptone fraction.

Key Words: binding • Escherichia coli heat-labile enterotoxin • glycoprotein • proteose-peptone

Submitted on March 9, 1993
Accepted on November 17, 1993




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