Coenzyme function of cobalamin analogues from calf kidney
J Thorndike and WS Beck
Calf kidney has been used as a tissue source for the isolation of cobalamin
analogues, which are defined here as cobalt-containing compounds of
distinctive chromatographic behavior that are extractable from tissues by
methods conventionally used to extract cobalamin and which, in radioisotope
dilution assays, are more active with R-protein as binder than intrinsic
factor and are relatively less active in microbiologic assays. Preparatory
methods employed reverse affinity chromatography or a series of chemical
extractions for the isolation of corrin followed by Dowex-50
chromatography. An analogue-containing fraction (peak 2) was eluted by
acetate buffers between pH 4 and 5. This material was shown to contain
cobalt, to migrate differently than the four cobalamins in Dowex-50 and
paper chromatography, and to display a pattern of properties that is
compatible with the above definition of cobalamin analogues. These
analogues stimulated crude preparations of
N5-methyltetrahydrofolate-homocysteine methyltransferase (EC 2.1.1.13) from
Escherichia coli and rat liver at far lower concentrations (1-40 nmol/L)
than the major cobalamins. No evidence of enzymatic conversion of cobalamin
to analogue could be demonstrated.
Volume 64,
Issue 1,
pp. 91-98,
07/01/1984
Copyright © 1984 by The American Society of Hematology
