Conformational changes accompanying the binding of antithrombin III to thrombin

Abstract

The conformational aspects of the binding of [human] antithrombin III to thrombin were investigated by difference spectroscopy, circular dichroism [CD] and optical rotatory dispersion [ORD]. The CD and ORD studies indicated an increase of 6-8% in .alpha.-helix content at the expense of the .beta.-structure, while the results from difference spectroscopy showed an increased exposure of approximately 7 tyrosine residues. With heparin there was a slightly greater increase in helicity which was accompanied by exposure of an average of 1 tyrosine and 2 tryptophan residues. These spectral results indicated that the thrombin-antithrombin III complex formed with heparin differs in its conformation from that produced without it.