The intercellular content of the three transcobalamins at various stages of normal and leukaemic myleoid cell development.

A study of the three serum transcobalamins (TC) in myeloproliferative disorders and acute leukaemia has suggested a granulocyte origin for the three binders; the later stages of this cell line might be releasing 'TC I' and 'TC III' while 'TC II' which is increased in sera from patients with acute myelogenous leukaemia, probably originates at least in part from myeloblasts. The intracellular content of each TC has been studied in normal and leukaemic bone marrow cells after separation on a discontinuous bovine serum albumin gradient. Myeloblasts contain a TC II-like protein almost exclusively but promyelocytes contain a TC I-like protein which increases as the cells mature whilst 'TC II' decreases. A TC III-like binder parallels 'TC I' but appears later and reaches a maximum in the polymorphonuclear cells. In various types of leukaemia, abnormal TC distributions are related either to marrow replacement by the blast cells or to a disorder of the maturation process in the leukaemic cell line.