Heme binding to human alpha-1 proteinase inhibitor

► A role of non-traditional plasma heme scavengers is evaluated. ► Human α1-PI and Hp are examined for binding with heme, PPIX and BR. ► Methods include UV/Vis, fluorescence, SPR, CD and functional assays. ► This study for the first time defines human α1-PI as a heme binding protein. ► Affinity of α1-PI to heme is of the same order of magnitude as that of albumin.