The Elution of 51Cr from Labelled Leukocytes —a New Theory

Abstract

Abstract Chromium-51 elutes rapidly from labelled leukocytes and tumor cells both in vitro and in vivo. Eluted 51Cr is dialysable and is not precipitated with trichloracetic acid and it has therefore been assumed to be free chromium which has dissociated from the labelled cellular protein. In vitro studies with 51Cr-labelled albumin have, however, demonstrated the extreme stability of the covalent bond between chromium and protein. Paper electrophoresis experiments are here described which show that the 51Cr which elutes from labelled mouse peritoneal cells behaves electrophoretically like 51Cr-labelled peptides and not at all like free 51Cr in either hexavalent or trivalent forms, or 51Cr-labelled lysine and arginine. Whole body counting studies after the intravenous injection of the various 51Cr preparations into mice indicate that eluted 51Cr and 51Cr-labelled peptides also have similar biologic behavior. Together, the electrophoretic and whole body counting studies exclude the presence of significant amounts of free 51Cr (either hexavalent or trivalent) in the 51Cr that elutes from labelled cells and supports the hypothesis that 51Cr elution results from turnover of labelled protein within the cell and loss of non-reutilisable labelled protein fragments. Confirmation of this theory would provide a powerful technic for the study of intra and extracellular protein metabolism.