Absorption of vitamin B12 by the guinea-pig. II. The subcellular localization of cyano-, methyl- and adenosyl-cobalamins and the effect of fluoroacetate on cyanocobalamin absorption.

Abstract

Summary.The gastrointestinal distribution and subcellular localization of radioactivity in the ileum of the guinea‐pig was determined 2 hr after oral feeding of physiological doses of cyano‐, methyl‐ and 5′ desoxyadenosyl‐cobalamin. The gastrointestinal distribution of the three analogues was similar although the uptake of methyl‐ and adenosylcobalamin by the ileum was less than that of cyanocobalamin. All three analogues were significantly localized in the mitochondrial fraction of the ileal mucosa during absorption.Guinea‐pigs were injected with sodium fluoroacetate, a drug which is thought to interfere with the conversion of cyano‐ to adenosylcobalamin. Large doses of the drug caused a marked delay in gastrointestinal transit. The subcellular distribution of radioactivity in the ileum was similar in the control group and those pretreated with a small dose (5μg/100 g) of fluoroacetate.It is concluded that the mitochondrial localization of vitamin B12 during absorption by the ileum plays a fundamental role in the transport of the vitamin but that interconversion of cyano‐ to adenosylcobalamin is not the reason for this localization.