Carboxyglutamic acid (Gla) containing proteins of human calcified atherosclerotic plaque solubilized by EDTA. Molecular weight distribution and relationship to osteocalcin.

Proteins containing the calcium binding amino acid, gamma-carboxyglutamic acid (Gla), are abundant in calcified human atherosclerotic plaque, but are detectable only at trace levels in the normal arterial wall and non-mineralized atherosclerotic lesions. These proteins have been incompletely characterized, and their role in the pathophysiology of atherosclerosis is not known. The present study sought to determine the overall molecular weight distribution of the calcified plaque Gla-protein fraction solubilized by EDTA demineralization and the possible relationship of these proteins to the bone Gla-protein, osteocalcin. Calcified atheromata were demineralized with EDTA (0.5 M, pH 6.9) for 7 days and the dialyzed EDTA extract subjected to procedures which specifically labeled the protein-bound Gla-residues with tritium. The EDTA solubilized Gla-protein fraction (19.5% of the total Gla) was separated by gel filtration high performance liquid chromatography which demonstrated a single broad radiolabeled Gla-protein peak with an approximate molecular weight of 6000 daltons. In addition the EDTA solubilized atherosclerotic Gla-proteins could be distinguished from the bone Gla-protein, osteocalcin (molecular weight = 5700 daltons), by reverse phase HPLC and specific radioimmunoassays for osteocalcin. It is concluded that the Gla-proteins of human calcified atherosclerotic plaque solubilized with EDTA demineralization consist of a heterogeneous 6000 dalton fraction, which is apparently unrelated to the bone Gla-protein, osteocalcin.