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Journal of Dairy Science Vol. 54 No. 4 461-466
© 1971 by American Dairy Science Association ®
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Interaction of {alpha}S1-Casein with Polyethylenimine1

W. R. Kason, S. Nakai and R. J. Bose

Department of Food Science, University of British Columbia
and Fisheries Research Board of Canada, Vancouver 8, British Columbia, Canada

ABSTRACT

{alpha}S1-Casein reacted with polyethylenimine, PEI 1000, flocculating at pH 9.5 but dissolved completely in 4 M urea. Polyethylenimine, containing 16% nitrogen, of which 20% is primary amine, migrated to the cathode by polyacrylamide gel electrophoresis at pH 7.0 and retarded the migration of {alpha}S1-casein when run as a mixture. Polyethylenimine revealed a single broad peak at 3.1 ppm in the high resolution nuclear magnetic resonance spectrometer which was almost pH insensitive. However, in the presence of {alpha}S1-casein, the PEI peak shifted to 3.3 ppm at pH 9.7 and approached 3.1 ppm as the pH was increased to 11.0. At pH 9.7 the resonance signals for the PEI-{alpha}S1-casein mixture were broader than those for each component indicating the formation of PEI-protein complex. A circular dichroic spectrum of {alpha}S1-casein was not affected by combining PEI, indicating no conformational change. Ultracentrifugation of the mixture of PEI 1000 and {alpha}S1-casein showed an interaction peak sedimenting slightly faster than {alpha}S1-casein.

The interaction of PEI 1000 with {alpha}S1-casein was pH and concentration dependent and dissociated in urea above 4 M and by increased pH, suggesting that the polymer associated at an electronegative region of the casein.

FOOTNOTES

1 Supported by Operating Grant A-3641 of the National Research Council of Canada.






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Copyright © 1971 by the American Dairy Science Association ®.