Spin-label studies of the sulfhydryl environment in bovine plasma albumin. 2. The neutral transition and the A isomer

Abstract

The investigation revealing sulfhydryl location in the crevice which opens during N-F transition was extended by characterizing the environment during the N-B transition and in the A isomer. The N-B and N-F transitions are very similar in that the sulfhydryl group moves from a restricted to unhindered environment during both. The use of the molecular dipstick technique further demonstrated the similarity between the F and A forms. Since A is a covalently stabilized form of albumin after a pH dependent transition, it retains its properties during subsequent pH changes rather than reverting to the N form. Spin-labeled A was titrated through the pH range of the acidic transitions without detecting the N-F transition. Isoelectric focusing analysis of A generated during alkaline aging and purified by SP-Sephadex chromatography indicates that it is a mixture of a small number of albumin forms rather than the large number of components once thought to be formed during aging.