THE MECHANISM OF 2,2,2-TRICHLOROACETIC ACID-INDUCED PROTEIN PRECIPITATION

The mechanism of 2,2,2-trichloroacetic acid (TCA)-induced precipitatio n of proteins is studied. The TCA-induced protein precipitation curves are observed to be U-shaped. It is bound that the protein-precipitate -inducing effects of TCA are due to the three chloro groups in the mol ecule. Using cardiotoxin III (CTX III) isolated from the Taiwan cobra (Naja naja atra), as a model protein, we attempt to understand the mol ecular basis for the TCA-induced effects. Employing circular dichroism , proton-deuterium exchange in conjunction with conventional 2D NMR te chniques, and 1-anilino naphthalene-8-sulfonate-binding experiments, w e demonstrate that CTX III is in a partially structured state similar to the 'A state' in 3% w/v TCA. It is postulated that the formation of this 'sticky' partial structured 'A state' in the TCA-induced unfoldi ng pathway is responsible for the acid-induced protein precipitation.