Structural arrangement in the α2‐macroglobulin—thrombin complex

Abstract
The cysteine sulfhydryl groups of α2-macroglobulin (α2M) generated upon thrombin complex formation are in contact with the proteinase surface as evidenced by singlet—singlet energy transfer measurements from N-(iodoacetylaminoethyl)-5-naphthylamine-1-sulfonic acid-labeled thiol functions of α2M to fluorescein isothiocyanate-labeled thrombin. The thrombin-α2M binding is normally covalent, but the presence of hydroxylamine during the reaction leads to the formation of a non-covalent complex. The transfer energy determinations show that the α2M binding sites of thrombin are quite similar, whatever covalent or non-covalent binding occurs.