PH-jump of pepsin studied by tyrosine ionization.

Abstract

Rapid conformational changes of pepsin occurring within 5 s due to pH-jump were studied by the stopped-flow method through the absorption change at 245 nm which is caused by the ionization of tyrosine residues. Two distinct phases of conformational change involving the exposure of tyrosine residues, perhaps buried in native pepsin, were observed. The pH profile of absorption change caused by the alkaline denaturation, Δ A, suggests that the unfolding in the slower phase occurs in lower pH than that in faster phase and that tyrosine residues exposed in the faster phase are more perturbed in the folded state than those exposed in the slower phase.