Interaction of urea with the high molecular weight protein fraction, carmin, from safflower seed (Carthamus tinctorius).

The effect of urea on the high molecular weight protein fraction, carmin, from
safflower seed Carthamus tinctorius L, was investigated by the techniques of
sedimentation velocity, viscosity, fluorescence and difference spectral measurements,
partial specific volume and circular dichroism. The protein underwent
dissociation and denaturation simultaneously in the presence of increasing concentration
of urea. The protein dissociated to a 2 s component and in the process,
the buried and exposed residues of tyrosines and tryptophans were perturbed.
At 8 M urea concentration, the protein existed completely as a random
coil; nearly 535 rnol of urea were bound per mol of protein. The results indicated
that the subunits of carmin appears to be held principally by noncovalent
interactions and are dissociated/denaturated by increasing concentration of urea,
leading to the destabilization of the native oligomer.