1. The effects of haemorrhage on vitamin B 12 (cobalamin) homoeostasis have been studied in rats with and without prior administration of 57 Co-labelled cyanocobalamin. 2. Arteriovenous differences in radioactivity and endogenous B 12 were measured across the thigh extensor muscles. Radioactivity and endogenous B 12 were also measured in skeletal muscle, liver and kidney. 3. Haemorrhage induced a marked rise in circulating B 12 with a concomitant loss of the vitamin from skeletal muscle and liver, but in kidney there was a net gain. Restoration of the blood volume with autologous plasma did not prevent release of B 12 from tissues. 4. The results suggest that vitamin B 12 reserves may be seriously depleted by the wasting of skeletal muscle.

1. Plasma samples from ten mammals were chromatographed on Sephadex G-200 columns and the total cobalamin content of each fraction was determined. 2. Unlike the situation in man, the bulk of the endogenous plasma cobalamin was found attached to a transcobalamin II-like protein in all ten animals. Transcobalamin 0 carried between 3 and 20%and this proportion appeared to be inversely related to the plasma total cobalamin. No endogenous cobalamin peak corresponding to transcobalamin I was detected in any species, though in the rabbit 5·3% of the plasma total cobalamin was attached to a protein of apparent molecular weight 176 000.

1. Serum from normal subjects has been chromatographed on Sephadex G-200 columns and the fractions containing transcobalamins 0, I and II have been identified. 2. The fractions corresponding to transcobalamin I contained, on average, 90% of the endogenous vitamin B 12 . Only 3% was attached to transcobalamin 0, and 7% was bound to transcobalamin II.

1. The case is described of a child with retarded physical and mental development, recurrent megaloblastic anaemia, methylmalonic aciduria and abnormal homocysteine metabolism resulting from an inborn error in the metabolism of cobalamins. She died at the age of 7 years. At autopsy there was pulmonary fibrosis and the brain showed lesions typical of those seen in subacute combined degeneration of the cord. 2. A metabolic abnormality was present which resulted in an inability to maintain normal tissue concentrations of the two coenzyme forms of vitamin B 12 , methylcobalamin and adenosylcobalamin. Lack of methylcobalamin led to deficient activity of N 5 -methyltetrahydrofolate-homocysteine methyltransferase with reduced ability to methylate homocysteine, and lack of adenosylcobalamin to deficient activity of methylmalonyl-CoA mutase, which accounted for the methylmalonic aciduria. 3. Analyses of total vitamin B 12 and of individual cobalamins by a chromatobioautographic technique showed that in organs sampled at autopsy, the content of total vitamin B 12 and of methylcobalamin, adenosylcobalamin and hydroxocobalamin were all greatly reduced. The plasma had a high normal total vitamin B 12 content, but showed a gross abnormality in the distribution of individual cobalamins, methylcobalamin being decreased and adenosylcobalamin and hydroxocobalamin increased. The erythrocytes showed a reduction in cobalamins resembling that in the solid organs, though less severe. 4. The underlying abnormality in this patient appeared to be either a defect in cellular uptake of vitamin B 12 , or a defect in a metabolic pathway leading to the formation of a common precursor of methylcobalamin and adenosylcobalamin. Abnormalities in transcobalamins I and II, plasma factors involved in plasma transport and cellular uptake of vitamin B 12 , were excluded. 5. The clinical and biochemical findings in the patient are compared with those described in three patients previously reported, who had methylmalonic aciduria and homocystinuria, and who were in some respects similar to this patient. The present case is unusual in that previous examples of errors in cobalamin metabolism have not had megaloblastosis or neurological changes typical of vitamin B 12 deficiency. It is also the first case in which direct estimations of individual cobalamins have been made.

1. Chromato-bioautographic analysis of cobalamins in Nigerian subjects showed that in patients with tropical ataxic neuropathy as in normal control subjects methylcobalamin was the major form of vitamin B 12 in plasma. Plasma cyanocobalamin was significantly higher in patients than control subjects. The concentration of plasma adenosylcobalamin in patients was about twice that in control subjects. 2. Adenosylcobalamin was the predominant liver cobalamin in all subjects. Cyanocobalamin was not detected in liver from normal subjects, but a small proportion of cyanocobalamin was detected in the liver in the majority of the patients. 3. The raised cyanocobalamin levels may have resulted from the chronic cyanide intoxication known to exist in these patients. There was no evidence of tissue vitamin B 12 deficiency or that conversion of metabolically active cobalamins into cyanocobalamin plays a part in the pathogenesis of tropical ataxic neuropathy. However, the increase in plasma adenosylcobalamin does indicate some disturbance of bodily handling of cobalamins in this disease.

1. Methylcobalamin (Me-B 12 ), adenosylcobalamin (Ado-B 12 ), hydroxocobalamin (OH-B 12 ) and cyanocobalamin (CN-B 12 ) have been estimated by a chromatographic—bioautographic technique in plasma, erythrocytes, leucocytes and bone marrow from normal subjects, hospital controls and patients with untreated pernicious anaemia. 2. Estimates of concentrations of cobalamins have also been obtained in bile, cerebrospinal fluid, liver biopsies and in autopsy samples of liver, kidney, spleen, brain and pituitary. 3. In normal and control subjects, Ado-B 12 predominated in all samples except plasma, in which Me-B 12 was the predominant form. Me-B 12 , Ado-B 12 , OH-B 12 and CN-B 12 were found in normal erythrocytes, leucocytes and bone marrow and the proportion of each cobalamin was fairly similar in all these tissues. In liver, kidney, spleen, brain and pituitary, the proportions of the cobalamins were more variable. No CN-B 12 was detected in these organs. 4. In untreated pernicious anaemia, Me-B 12 was disproportionately reduced in plasma, but not in erythrocytes, leucocytes or bone marrow. There was a small increase in the proportion of CN-B 12 in plasma, blood cells and bone marrow in untreated pernicious anaemia.

1. This paper reports a survey of values for individual plasma cobalamins in normal subjects, hospital controls, and patients with vitamin B 12 deficiency and diseases in which there are disturbances of B 12 metabolism. The values were obtained by thin-layer chromatography and bioautography followed by photometric scanning or visual assessment. 2. Normal plasma contains methylcobalamin (the predominant component), deoxyadenosylcobalamin and hydroxocobalamin. The latter two compounds are not separable in the solvent system routinely used. In some samples there were traces of cyanocobalamin. The ratio of methylcobalamin to deoxyadenosylcobalamin plus hydroxocobalamin, normally greater than 1·0, was reduced in B 12 deficiency. Many cases of untreated pernicious anaemia showed a high proportion (up to 40%) of cyanocobalamin. In folate deficiency there was no consistent change in individual cobalamins. Patients with leukaemias and liver disease showed a variety of changes, some attributable to alterations in plasma binding capacity and loss of deoxyadenosylcobalamin from the liver. 3. After oral or parenteral administration of cyanocobalamin, plasma cyanocobalamin increased and there was evidence of conversion to methylcobalamin. After parenteral administration of methylcobalamin, this compound increased in the plasma, but deoxyadenosylcobalamin plus hydroxocobalamin did not change. 4. Possible reasons for pathological changes in individual plasma cobalamins are discussed.