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Journal of Dairy Science Vol. 50 No. 4 456-460
© 1967 by American Dairy Science Association ®
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Effect of Modifying Histidine Residues in {kappa}-Casein on Its Stabilizing Ability1

S. Nakai2, H. K. Wilson and E. O. Herreid

Department of Food Science, University of Illinois, Urbana

ABSTRACT

Histidine residues were decreased 0.5 and 1.5 in 5 for 28,000 g of diisopropylphosphorylated (DIP) and carboxymethylated (CM) {kappa}-caseinates at pH 5.5. Stabilizing abilities of these {kappa}-caseinates were unchanged. Oxidation with periodate and 2-phenyl-1, 4-dibromoacetoin (PDA) at pH 6.6 decreased stabilizing abilities, which were restored by 0.2 N NaOH.

Optical density ratios at 280 mµ and pH 12, and at 220 mµ and pH 7 were 0.07, 0.12, and 0.20 for {kappa}-casein, and PDA-{kappa}-casein alkylated at pH 6.6 and 7.5, respectively, indicating acceptance of more phenyl groups as alkylation progressed.

Stabilizing abilities of sterilized and stored {kappa}-caseinates, of which histidine residues were masked by sterilization and storage, were partly restored with 0.2 N NaOH at 25 C for 30 min. Reoxidation of PDA-alkylated {kappa}-caseins after reduction did not change the gel-filtrated elution patterns obtained with 0.2 N NaOH at 4 C on Sephadex G-200.

Gel electrophoresis revealed effects of storage on {kappa}-casein that were different from those of rennin action. The peaks moved faster, bound less dye than the control, and bands of the subfractions did not separate clearly. Two fast moving bands separated from the main zone of stored {kappa}-casein in the early stages.

FOOTNOTES

1 Supported by a grant from the American Dairy Association, 20 Wacker Drive, Chicago, Illinois.

2 Department of Animal Science, University of British Columbia, Vancouver, B. C., Canada.






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Copyright © 1967 by the American Dairy Science Association ®.