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Related Experiment Videos

pH-induced structural transitions of caseins.

Asima Chakraborty1, Soumen Basak

  • 1Chemical Sciences Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064, India.

Journal of Photochemistry and Photobiology. B, Biology
|June 1, 2007
PubMed
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Milk caseins (alpha(s)-, beta-, and kappa-casein) undergo structural changes with pH. Acidic conditions promote folding by neutralizing charges, while near the isoelectric point (pI), they reach maximum structure, then partially unfold at lower pH.

Area of Science:

  • Biochemistry
  • Protein Chemistry
  • Spectroscopy

Background:

  • Caseins are unstructured milk proteins (alpha(s)-, beta-, kappa-casein) lacking a defined fold due to low hydrophobicity and high net charge.
  • Understanding casein structure is crucial for dairy science and food technology.

Purpose of the Study:

  • To investigate the pH-dependent structural transitions of alpha(s)-, beta-, and kappa-casein.
  • To elucidate the relationship between pH, net charge, and casein conformation.

Main Methods:

  • Fluorescence spectroscopy (Tryptophan emission, ANS binding)
  • Circular Dichroism (CD) spectroscopy
  • Energy transfer measurements (Trp donor, ANS acceptor)

Main Results:

Related Experiment Videos

  • At neutral/alkaline pH, caseins exist in a random coil conformation.
  • Acidification leads to charge compensation and chain folding, with maximal structure near the isoelectric point (pI, pH 4-5).
  • Below pI, partial unfolding occurs due to re-emerging charge interactions.

Conclusions:

  • Casein structure is highly sensitive to pH-induced charge variations.
  • The observed structural transitions are consistent with electrostatic interactions governing protein conformation.
  • Spectroscopic methods effectively characterize these dynamic structural changes in caseins.