The tartrate-resistant purple acid phosphatase of bone osteoclasts—a protein phosphatase with multivalent substrate specificity and regulation

Abstract

Tartate-resistant purple acid phosphatases (TRAP/PAP) are iron-containing, cationic glycoproteins with molecular weights of around 35 kDa and a monomeric peptide structure (Vincent and Averill, 1990; Andersson et al, 1992). When isolated and sufficiently concentrated, these enzymes exhibit a characteristic purple color. The purple acid phosphatases of spleen and uterus have been extensively characterized, in particular with respect to the unique active site containing two iron atoms, which are essential for catalytic activity (Vincent and Averill 1990). This binuclear iron center can exist in two interconvertible states: in the purple enzyme as a diferric pair which is catalytically inactive or in the reduced, catalytically active pink species where the di-iron cluster exist as a mixed-valent Fe(II)-Fe(III) couple (Wang et al. 1992). Low levels of TRAP/PAP enzymes can be detected in most tissues, whereas much higher expression levels are detected in bones of growing animals (Ek-Rylander et al. 1991a). In ...