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The action of rennin on casein The disruption of the k-casein complex*

Published online by Cambridge University Press:  01 June 2009

R. Beeby  and
Hs. Nitschmann
R. Beeby
Affiliation:
Division of Dairy Research, C.S.I.R.O., Melbourne, Australia
Hs. Nitschmann
Affiliation:
Institute of Organic Chemistry, University of Berne, Switzerland
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Summary

Approximately 30% of the nitrogen of κ-casein was soluble at pH 4·7 after the protein had been treated with rennin at pH 7 while approximately 10% was soluble in 12% trichloroacetic acid (TCA). The material soluble in 12% TCA appeared at a slower rate initially than did the nitrogen soluble at pH 4·7 but as the reaction proceeded it was released more rapidly.

Treating κ-casein with urea, or repeated precipitation of the protein at pH 4·7, caused the formation of material insoluble at pH 7, apparently para-κ-casein. Both treatments appeared to free the same soluble fraction as does rennin acting in low concentration or for a short time.

Low concentrations of rennin (0·07 μg/ml) released only part of the available soluble nitrogen from 2% solutions of whole casein at pH 7. Heating the reaction mixture appeared to restore the casein complex, the restoration being less complete the longer the reaction had proceeded.

It is suggested that κ-casein is not a single protein but a complex, and that the action of rennin is first to open the secondary bonds responsible for the stability of this complex.

Type
Original Articles
Information
Journal of Dairy Research , Volume 30 , Issue 1 , February 1963 , pp. 7 - 16
Copyright
Copyright © Proprietors of Journal of Dairy Research 1963

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References

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