Properties of thiol-specific anti-oxidant protein or calpromotin in solution

We have isolated calpromotin, a protein reported abundant in human red cell s and shown to be of significance for KCl transport. We show that calpromot in is identical to a radical scavenger protein, thiol-specific antioxidant protein (TSA). Calpromotin is known to exist partially as a large complex o f identical subunits and partially as dimers probably held together by disu lfide bridges. The stability of the high-molecular-weight form was studied by variations of pH and urea concentration. It is shown that the equilibriu m between the large complex and the dimeric subunit is governed by the diss ociation of a group with a pK value of about 7.5. Dissociation of the compl ex was also complete at 2.5 M urea, where no unfolding of the peptide chain s was detectable. (C) 1999 Academic Press.