title: Coenzyme function of cobalamin analogues from calf kidney.
abstract: 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.
mesh_terms: D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002845:Chromatography; D003035:Cobalt / Q000032:analysis; D003067:Coenzymes / Q000378:metabolism*; D045728:Corrinoids; D004926:Escherichia coli / Q000201:enzymology; D007668:Kidney / Q000201:enzymology*; D014805:Vitamin B 12 / Q000031:analogs & derivatives* / Q000032:analysis / Q000302:isolation & purification
chemical_list: D003067:Coenzymes; D045728:Corrinoids; D003035:Cobalt; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D014805:Vitamin B 12