Effect of acidic pH on the protein carmin from safflower seed (Carthamus tinctorius)

The effect of a decrease in pH on the structural integrity of carmin has been monitored by a variety of biophysical techniques. The protein undergoes initial dissociation up to pH 3.5-4.0 without any significant denaturation. Below this pH the process of dissociation and denaturation appears to be simultaneous. Further, in the pH range of 2.5-1.6 the protein reassociates to probably a different polymer resulting from possibly, an entropically driven hydrophobic interaction. The process of dissociation appears to be reversible to a large extent. The process of denaturation appears to be governed by the kinetic path that the denatured protein molecule follows either by a sudden decrease in pH or through a gradual decrease in pH. These results are interpreted while keeping in view the oligomeric and globular structure of carmin at neutral pH. The results would help in understanding of structure-function relationship of the protein and its role in hydrogen ion binding in vivo.