Metallothionein in platelets.

The zinc content in platelets from rabbits, humans and horses was determined, and the levels of zinc were found to be significantly higher (3 micrograms/10(10) cells) than those in other peripheral blood cells. About 70% of the zinc in the supernatants of platelet lysates could be detected. From the results of gel filtration analysis, the zinc in platelet lysates was found to be bound with a low-molecular-weight protein (MW 6,000-8,000) detected as metallothionein (MT) on the basis of antigenic properties determined by enzyme-linked immunoassay and immunoblotting analysis using monoclonal antibodies raised against rabbit and horse MTs produced by murine hybridoma cell lines. The concentrations of MTs in the platelet lysates were quantitatively determined, and the average values were 30.5 +/- 3.7, 39.4 +/- 4.2 and 39.7 +/- 4.4 micrograms/10(10) cells for rabbit, human and horse platelets, respectively. The antibody against rabbit MT reacted not only with its homologous antigen but also with heterologous antigens, whereas the antibody against horse MT reacted only with its homologous antigen. The biological function of MTs in platelets is not yet understood, but it is possible that platelet MT serves to regulate the homeostasis of metals and/or to preserve metals indispensable for the activation of enzymes or cells. The present study demonstrated the presence of MT in platelets.