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

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.