PLASMA CLEARANCE OF 57COBALT-LABELLED VITAMIN B12 BOUND IN VITRO AND IN VIVO TO TRANSCOBALAMIN .I. AND .2

Radioactive-labelled B12 bound to transcobalamin I has an initial distribution volume twice the plasma volume, a fractional turnover rate of 45 to 60 per cent per day, a biologic half-life in plasma of 6 days and an extra-vascular distribution of 74 to 81 per cent. Transcobalamin II had a fractional turnover rate of 1536 and 1944 per cent per day, a biologic half-life of 12 hours and an extravascular distribution of 90 per cent. © 1969 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.