Summary
Histidine-proline-rich glycoprotein (HPRG) binds zinc, which in turn promotes HPRG
binding to lymphocytes and monocytes. We examined the possibility that zinc and other
transition metals also promote HPRG binding to platelets. Only non-specific, unsaturable
association of HPRG with resting or activated platelets was observed in the absence
of transition metals. However, nickel, cobalt, copper, cadmium, and zinc greatly increased
HPRG association with the cells. In the presence of zinc, specific, saturable binding
of HPRG to platelets was demonstrated. The cell binding capacity for HPRG could be
increased by increasing the zinc saturation of HPRG from 10% to 30% as well as by
activating the platelets with thrombin. Because platelets contain relatively high
concentrations of secretable zinc, it is possible that significant amounts of HPRG
bind to activated platelets at sites of blood clotting and that this has a physiologic
function.
Keywords
Histidine-proline-rich glycoprotein - platelets - fibrinolysis - zinc