Evaluation of the cobalt requirement of beef cattle based on vitamin B12, folate, homocysteine and methylmalonic acid

This investigation was designed to estimate the Co requirement of growing cattle on the basis of plasma and liver levels of vitamin B12 and folate, plasma levels of homocysteine and methylmalonic acid (MMA) and haematological variables. For this purpose thirty-four male intact cattle of the German Simmental breed (236 kg) were assigned randomly to ten groups and were fed corn silage-based diets which contained 70, 90, 109, 147, 184, 257, 327, 421, 589 or 689 μg Co/kg DM for 40 weeks. One-slope broken-line model analysis and a quadratic model with plateau were used to estimate the Co requirement. The broken-line model estimated the dietary Co requirement of growing cattle to be 257 (SE 29) ΜG/KG DIETARY DM BASED ON PLASMA VITAMIN B12 AS RESPONSE CRITERION. THE DIETARY CO LEVELS NEEDED TO MAXIMISE THE LIVER VITAMIN B12 AND LIVER FOLATE WERE 236 (se 8) and 190 (se 8) μg/kg dietary DM respectively. Plasma folate did not show any response to the different Co levels. The dietary Co was inversely correlated with the plasma concentrations of homocysteine and MMA. Estimates of the dietary Co concentration required to minimise homocysteine were 161 (se 10) μg/kg DM. When MMA was used as response criterion, the linear model yielded a Co requirement of 124 (se 3) μg/kg dietary DM. The quadratic model did not provide a better closeness of regression fit and yielded similar requirements to the linear model. Haemoglobin concentration and haematocrit tended to have a slight response to increasing dietary Co and were only decreased in cattle on diets containing less than 100 μg Co/kg DM. On the basis of the present data, recommended levels of dietary Co for normal folate metabolism and minimum homocysteine and MMA levels can be set to be 150–200 μg/kg DM; for maximum vitamin B12 levels, the desired Co content in the diet seems to be 250 μg/kg DM.

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Methylmalonic acid in the diagnosis of cobalt deficiency in barley-fed lambs

British Journal Of Nutrition ◽

10.1079/bjn19890073 ◽

1989 ◽

Vol 62 (3) ◽

pp. 729-738 ◽

Cited By ~ 24

Author(s):

F.P.M. O'Harte ◽

D. G. Kennedy ◽

W. J. Blanchflower ◽

D. A. Rice

Keyword(s):

Methylmalonic Acid ◽

Statistical Significance ◽

Plasma Concentrations ◽

Vitamin B ◽

Plasma Vitamin ◽

Elevated Plasma ◽

Normal Range ◽

Cobalt Deficiency ◽

Upper Level ◽

Liquid Chromatographic

Eight lambs were fed on a cobalt-deficient whole-barley diet supplemented with urea, vitamins and minerals. Four control lambs were fed on the same diet which had been further supplemented with Co. Plasma vitamin B12 levels in the Co-depleted group declined rapidly, falling below the normal range within 5 weeks. Differences between the live weights of the animals in the two groups approached statistical significance by week 14. However, methylmalonic acid (MMA) rose above normal levels in the Co-depleted group within 7 weeks. This suggested that an elevated plasma concentration of MMA is a comparatively early indicator of functional vitamin B12 deficiency. It is recommended that 10 μmol/l be the upper level of normality for plasma MMA concentration in barley-fed animals, in contrast with the level of 5 μmol/l for grass-fed animals. Changes in the plasma concentrations of MMA and ethylmalonic acid associated with feeding the barley-based diet per se did not significantly affect the validity of the gas-liquid chromatographic assay for MMA.

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Increased plasma homocysteine levels without signs of vitamin B12 deficiency in patients with multiple sclerosis assessed by blood and cerebrospinal fluid homocysteine and methylmalonic acid

Multiple Sclerosis Journal ◽

10.1191/1352458503ms918oa ◽

2003 ◽

Vol 9 (3) ◽

pp. 239-245 ◽

Cited By ~ 50

Author(s):

M Vrethem ◽

E Mattsson ◽

H Hebelka ◽

K Leerbeck ◽

A Österberg ◽

...

Keyword(s):

Multiple Sclerosis ◽

Cerebrospinal Fluid ◽

Methylmalonic Acid ◽

Haemoglobin Concentration ◽

Serum Vitamin ◽

High Serum ◽

Plasma Homocysteine ◽

Cobalamin Deficiency ◽

Vitamin B ◽

Plasma Thcy

Objective: The aim of this study was to evaluate if multiple sclerosis (MS) is associated with vitamin B12 (cobalamin) deficiency. Methods: We measured serum vitamin B12, plasma folate, serum methylmalonic acid (MMA), plasma homocysteine (tHcy) and also cerebrospinal fluid (C SF) MMA and tHcy in 72 patients with MS and 23 controls. Results: The mean plasma tHcy level was significantly increased in MS patients (11.6 mmol/L) compared with controls (7.4 mmol/L) (P =4-0.002). Seven patients showed low serum vitamin B12levels but only one of them had concomitant high plasma tHcy. None of them showed high serum MMA. Plasma or blood folate levels did not differ between MS patients and controls. We found no significant differences in mean values or frequency of pathological tests of serum B12, serum MMA, mean corpuscular volume (MC V), haemoglobin concentration, C SF tHcy or C SF MMA between patients and healthy subjects. There were no correlations between C SF and serum/plasma levels of MMA or tHcy. Serum vitamin B12, serum MMA, plasma tHcy, C SF Hcy or C SF MMA were not correlated to disability status, activity of disease, duration of disease or age. Conclusions:The relevance of the increased mean value of plasma tHcy thus seems uncertain and does not indicate functional vitamin B12 deficiency. We can not, however, exclude the possibility of a genetically induced dysfunction of the homocysteine metabolism relevant for the development of neuroinflammation/degeneration. O ur findings indicate that, regardless of a significant increase in plasma tHcy in MS patients, the MS disease is not generally associated with vitamin B12 deficiency since we did not find any other factors indicating vitamin B12 deficiency. A nalysis of C SF MMA and C SF tHcy, which probably reflects the brain vitamin B12 status better than serum, are not warranted in MS. We conclude that B12 deficiency, in general, is not associated with MS.

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Interactions between plasma concentrations of folate and markers of vitamin B12status with cognitive performance in elderly people not exposed to folic acid fortification: the Hordaland Health Study

British Journal Of Nutrition ◽

10.1017/s000711451300336x ◽

2013 ◽

Vol 111 (6) ◽

pp. 1085-1095 ◽

Cited By ~ 23

Author(s):

Esmée L. Doets ◽

Per M. Ueland ◽

Grethe S. Tell ◽

Stein Emil Vollset ◽

Ottar K. Nygård ◽

...

Keyword(s):

Cognitive Impairment ◽

Folic Acid ◽

Cognitive Performance ◽

Sex Education ◽

Plasma Concentrations ◽

Health Study ◽

Vitamin B ◽

Plasma Vitamin ◽

Folic Acid Fortification ◽

Plasma Folate

A combination of high folate with low vitamin B12plasma status has been associated with cognitive impairment in a population exposed to mandatory folic acid fortification. The objective of the present study was to examine the interactions between plasma concentrations of folate and vitamin B12markers in relation to cognitive performance in Norwegian elderly who were unexposed to mandatory or voluntary folic acid fortification. Cognitive performance was assessed by six cognitive tests in 2203 individuals aged 72–74 years. A combined score was calculated using principal component analysis. The associations of folate concentrations, vitamin B12markers (total vitamin B12, holotranscobalamin (holoTC) and methylmalonic acid (MMA)) and their interactions in relation to cognitive performance were evaluated by quantile regression and least-squares regression, adjusted for sex, education, apo-ɛ4 genotype, history of CVD/hypertension and creatinine. Cross-sectional analyses revealed an interaction (P= 0·009) between plasma concentrations of folate and vitamin B12in relation to cognitive performance. Plasma vitamin B12concentrations in the lowest quartile ( < 274 pmol/l) combined with plasma folate concentrations in the highest quartile (>18·5 nmol/l) were associated with a reduced risk of cognitive impairment compared with plasma concentrations in the middle quartiles of both vitamins (OR 0·22, 95 % CI 0·05, 0·92). The interaction between folate and holoTC or MMA in relation to cognitive performance was not significant. In conclusion, this large study population unexposed to mandatory folic acid fortification showed that plasma folate, but not plasma vitamin B12, was associated with cognitive performance. Among the elderly participants with vitamin B12concentrations in the lower range, the association between plasma folate and cognitive performance was strongest.

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Relationships between plasma methylmalonic acid and ruminal succinate in cobalt-deficient and -repleted sheep

Australian Journal of Agricultural Research ◽

10.1071/ar05125 ◽

2007 ◽

Vol 58 (4) ◽

pp. 367 ◽

Cited By ~ 1

Author(s):

S. C. Wiese ◽

C. L. White ◽

I. H. Williams ◽

J. G. Allen

Keyword(s):

Vitamin B12 ◽

Methylmalonic Acid ◽

Plasma Concentrations ◽

Plasma Vitamin ◽

Normal Range ◽

Deficient Diet ◽

Wool Growth ◽

Cobalt Deficiency ◽

Vitamin B12 Supplementation ◽

Effective Degree

We measured methylmalonic acid (MMA) in plasma and succinate in the rumen during the depletion of sheep to a state of severe cobalt deficiency and repletion by various forms of supplementation. Groups of 10, cobalt-deficient weaners were allocated to one of 4 treatments: no supplement, 0.1 or 4.0 mg/day of cobalt as a solution of CoSO4.7H2O per os, or intramuscular vitamin B12. Plasma concentrations of MMA were elevated above the normal range (5 µmol/L) after 35 days on the cobalt-deficient diet, before a reduction in feed intake and while liveweights were still increasing. In all 3 supplemented groups of sheep, plasma vitamin B12 concentrations increased to normal levels within 10 days of supplementation (P < 0.001). Plasma MMA concentrations were reduced to normal levels within 10 days with vitamin B12 supplementation but took 31 days with oral cobalt supplementation (P < 0.001). Plasma MMA concentration in the unsupplemented group continued to rise and remain high for the duration of the experiment and did not show the peak and decline to levels indistinguishable from cobalt adequate levels as observed by others. Rumen succinate concentrations were elevated within 6 days of sheep being introduced to a cobalt-deficient diet and in the unsupplemented sheep remained elevated for the duration of measurement. This rise in rumen succinate was seen at a wider range of cobalt intakes than previously reported. In both oral cobalt treatments, vitamin B12 concentrations increased (P < 0.001) and succinate concentrations decreased (P < 0.001) in the rumen to normal levels within 6 days of supplementation. However, the vitamin B12 provided to the sheep by injection was not recycled to the rumen to any effective degree, as demonstrated by the persistence of high rumen succinate concentrations. The ability of the vitamin B12-supplemented sheep to maintain higher rates of wool growth than deficient sheep, while still exhibiting elevated succinate concentrations in the rumen, demonstrates that overcoming the blockage of the methylmalonyl CoA mutase pathway in the rumen is not essential for restoring metabolic pathways such as those responsible for wool growth. This work contributes to the knowledge of plasma MMA and rumen succinate as useful indicators of functional cobalt status and cobalt intake in sheep.

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Effects of folic acid and vitamin B12 supplements on folate and homocysteine metabolism in pigs during early pregnancy

British Journal Of Nutrition ◽

10.1079/bjn2002653 ◽

2002 ◽

Vol 88 (3) ◽

pp. 253-263 ◽

Cited By ~ 19

Author(s):

Frédéric Guay ◽

J. Jacques Matte ◽

Christiane L. Girard ◽

Marie-France Palin ◽

Alain Giguère ◽

...

Keyword(s):

Folic Acid ◽

Present Experiment ◽

Binding Capacity ◽

Plasma Concentrations ◽

Total Content ◽

Plasma Homocysteine ◽

Vitamin B ◽

Plasma Vitamin ◽

Diet Supplements ◽

Uterine Secretions

The present experiment aimed to determine the effects of supplements of folic acid (FA) alone or in combination with vitamin B12 on folate and homocysteine metabolism in gestating nulliparous Yorkshire–Landrace (YL) and multiparous Landrace (LD) occidental sows and multiparous Chinese Meishan–Landrace (ML) sows. LD sows were randomly assigned to two treatments: 0 or 15 mg FA/kg diet while YL and ML sows were assigned to three treatments: 0 mg FA/kg diet, 15 mg FA/kg or 15 mg FA+160 μg vitamin B12/kg diet. Supplements were given from the oestrus preceding insemination up to slaughter on day 15 of gestation. At slaughter, a uterine flush was collected to determine uterine contents of homocysteine, methionine, tetrahydrofolate (THF), 5-methyl-THF, pyridoxal 5-phosphate (P5P) and vitamin B12. Blood samples were taken at first oestrus, at insemination and on days 5, 10 and 15 of gestation to determine plasma concentrations of homocysteine, methionine, THF, 5-methyl-THF, P5P, vitamin B12 and relative total folate-binding capacity. In occidental sows (YL and LD), the FA supplement tended to decrease uterine flush content of homocysteine (P=0·06) and concentrations of plasma homocysteine (P=0·09). Nulliparous YL sows had lower concentrations of plasma homocysteine, methionine, THF and 5-methyl-THF (P<0·05) than multiparous LD sows. Multiparous ML and LD sows had similar concentrations of plasma THF, 5-methyl-THF, methionine and vitamin B12, but ML sows had lower concentrations of plasma homocysteine (P<0·05). The vitamin B12 supplement increased concentrations of plasma vitamin B12 (P<0·05) both in multiparous ML and nulliparous YL sows, but had no effect on the composition of either uterine flush or plasma. The present results showed also that sows had a low vitamin B12 status (<200 pg/ml) and high circulating homocysteine levels (>15 μM) during the first 15 d of gestation. Furthermore, the vitamin B12 content in uterine secretions represented between 180 and 300 % of the total content in plasma. The low plasma concentrations of homocysteine in multiparous ML sows suggest a more efficient remethylation pathway which may not be dependent upon dietary supply of FA or vitamin B12. In nulliparous YL sows, low concentrations of both homocysteine and methionine suggest that the methionine requirement for protein deposition might have reduced the amount of methionine available for the methylation pathway. The results of the present experiment suggest that the reduction of uterine homocysteine may be an important aspect of the role of FA supplement on the uterine environment in occidental sows. The presence of high levels of vitamin B12 in uterine secretions merits further investigation in relation to embryonic development.

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Intakes of Vitamin B-12 from Dairy Food, Meat, and Fish and Shellfish Are Independently and Positively Associated with Vitamin B-12 Biomarker Status in Pregnant Dutch Women

Journal of Nutrition ◽

10.1093/jn/nxy233 ◽

2018 ◽

Vol 149 (1) ◽

pp. 131-138 ◽

Cited By ~ 1

Author(s):

Karlijn F M Denissen ◽

Sandra G Heil ◽

Simone J P M Eussen ◽

Jim P J Heeskens ◽

Carel Thijs ◽

...

Keyword(s):

Pregnant Women ◽

Methylmalonic Acid ◽

Dietary Vitamin ◽

Birth Cohort Study ◽

Vitamin B ◽

Plasma Vitamin ◽

Total Vitamin ◽

Dairy Food ◽

Vitamin B 12 ◽

Fish And Shellfish

ABSTRACTBackgroundThe effect of vitamin B-12 from different animal foods on vitamin B-12 biomarker status has not previously been evaluated in pregnant women.ObjectiveWe examined the association of vitamin B-12 intake from dairy, meat, fish (including shellfish), and eggs with circulating concentrations of vitamin B-12 biomarkers and with the presence of vitamin B-12 deficiency in 1266 pregnant women participating in the KOALA Birth Cohort Study.MethodsBlood samples were collected in weeks 34–36 of pregnancy, and vitamin B-12 intake from foods and supplements was estimated with a semiquantitative food-frequency questionnaire (FFQ). Total vitamin B-12, holotranscobalamin (holoTC), and methylmalonic acid (MMA) were determined in plasma. Vitamin B-12 deficiency was defined as holoTC <35 pmol/L and MMA >0.45 μmol/L. Associations were evaluated with linear and logistic regression analyses, adjusting for potential confounders.ResultsSignificant dose-response relations were observed between vitamin B-12 intake from dairy, meat, and fish and plasma vitamin B-12, holoTC, and MMA [P-trend for (shell)fish with MMA = 0.002; P-trend for dairy, meat, and fish with all other markers < 0.001]. The OR (95% CI) of vitamin B-12 deficiency in the third compared with the first tertile of dairy-derived vitamin B-12 was 0.13 (0.04, 0.49), and the ORs for vitamin B-12 from meat and fish were 0.33 (0.11, 0.97) and 0.25 (0.08, 0.82), respectively. Egg-derived vitamin B-12 was only associated with holoTC. Additional analyses showed that self-defined vegetarians and FFQ-defined lacto-ovo-vegetarians had lower median total dietary vitamin B-12 intake and considerably worse vitamin B-12 biomarker status than omnivores and pescatarians.ConclusionsIn pregnant Dutch women, higher intakes of vitamin B-12 from dairy, meat, and fish were positively associated with vitamin B-12 status, suggesting that dairy, meat, and fish are good sources of bioactive vitamin B-12 in pregnancy. Nevertheless, for (lacto-)vegetarians, vitamin B-12 supplementation is recommended.

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Plasma free choline, betaine and cognitive performance: the Hordaland Health Study

British Journal Of Nutrition ◽

10.1017/s0007114512001249 ◽

2012 ◽

Vol 109 (3) ◽

pp. 511-519 ◽

Cited By ~ 22

Author(s):

Eha Nurk ◽

Helga Refsum ◽

Ingvar Bjelland ◽

Christian A. Drevon ◽

Grethe S. Tell ◽

...

Keyword(s):

Regression Model ◽

Cognitive Performance ◽

Word Association ◽

Block Design ◽

Plasma Concentrations ◽

Cognitive Testing ◽

Health Study ◽

Vitamin B ◽

Plasma Vitamin ◽

Free Choline

Choline and betaine are nutrients involved in one-carbon metabolism. Choline is essential for neurodevelopment and brain function. We studied the associations between cognitive function and plasma concentrations of free choline and betaine. In a cross-sectional study, 2195 subjects (55 % women), aged 70–74 years, underwent extensive cognitive testing including the Kendrick Object Learning Test (KOLT), Trail Making Test (part A, TMT-A), modified versions of the Digit Symbol Test (m-DST), Block Design (m-BD), Mini-Mental State Examination (m-MMSE) and Controlled Oral Word Association Test (COWAT). Compared with low concentrations, high choline (>8·4 μmol/l) was associated with better test scores in the TMT-A (56·0v. 61·5,P= 0·004), m-DST (10·5v. 9·8,P= 0·005) and m-MMSE (11·5v. 11·4,P= 0·01). A generalised additive regression model showed a positive dose–response relationship between the m-MMSE and choline (P= 0·012 from a corresponding linear regression model). Betaine was associated with the KOLT, TMT-A and COWAT, but after adjustments for potential confounders, the associations lost significance. Risk ratios (RR) for poor test performance roughly tripled when low choline was combined with either low plasma vitamin B12( ≤ 257 pmol/l) concentrations (RRKOLT= 2·6, 95 % CI 1·1, 6·1; RRm-MMSE= 2·7, 95 % CI 1·1, 6·6; RRCOWAT= 3·1, 95 % CI 1·4, 7·2) or high methylmalonic acid (MMA) ( ≥ 3·95 μmol/l) concentrations (RRm-BD= 2·8, 95 % CI 1·3, 6·1). Low betaine ( ≤ 31·1 μmol/l) combined with high MMA was associated with elevated RR on KOLT (RRKOLT= 2·5, 95 % CI 1·0, 6·2). Low plasma free choline concentrations are associated with poor cognitive performance. There were significant interactions between low choline or betaine and low vitamin B12or high MMA on cognitive performance.

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Hypoxia-induced megaloblastosis in vitamin B12-deficient rats

British Journal Of Nutrition ◽

10.1079/bjn2002811 ◽

2003 ◽

Vol 89 (4) ◽

pp. 441-444 ◽

Cited By ~ 9

Author(s):

Shuhei Ebara ◽

Satoko Adachi ◽

Shigeo Takenaka ◽

Toshiki Enomoto ◽

Fumio Watanabe ◽

...

Keyword(s):

Mean Corpuscular Volume ◽

Human Subjects ◽

Haemoglobin Concentration ◽

Megaloblastic Anaemia ◽

Erythrocyte Count ◽

Dietary Vitamin ◽

Hypoxic Exposure ◽

Vitamin B ◽

Plasma Vitamin ◽

Serum Erythropoietin

In rats, in contrast with human subjects who develop megaloblastic anaemia due to vitamin B12deficiency, haematological abnormalities with anaemia were not observed under normoxic conditions even though plasma vitamin B12concentration was reduced to <15 % of a normal concentration by depleting dietary vitamin B12. To elucidate whether erythropoiesis was affected by vitamin B12deficiency in rats, these vitamin B12-deficient rats were exposed to hypoxia (10·5 % O2) to stimulate erythropoiesis. In the vitamin B12-sufficient control rats, erythrocyte count was significantly (P<0·05) increased 1 week after starting the hypoxic exposure. However, the hypoxia-induced erythropoiesis was affected by vitamin B12deficiency, and no significant increase in the erythrocyte count was observed even after 6-week exposure to hypoxia in the vitamin B12-deficient rats. In the vitamin B12-deficient rats in hypoxia, erythrocytes became abnormally enlarged, and haemoglobin concentration in peripheral blood was increased in proportion to the increase of mean corpuscular volume. However, the level of the increase in the haemoglobin concentration was significantly (P<0·05) lower in the vitamin B12-deficient rats compared with that in the -sufficient controls. In addition, in the vitamin B12-deficient rats, in contrast to the -sufficient rats, serum erythropoietin concentration was not normalized even after 6-week exposure to hypoxia. These results indicate that a megaloblastic anaemia-like symptom is induced when the vitamin B12-deficient rats are exposed to hypoxia.

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Plasma Vitamin B12, Methylmalonic Acid and Heart Rate Variability in Healthy Young Indian Adults

International Journal for Vitamin and Nutrition Research ◽

10.1024/0300-9831/a000155 ◽

2013 ◽

Vol 83 (3) ◽

pp. 147-153 ◽

Cited By ~ 4

Author(s):

Sambashivaiah Sucharita ◽

Sharma Sowmya ◽

Tinku Thomas ◽

Anura V. Kurpad ◽

Mario Vaz

Keyword(s):

Heart Rate ◽

Heart Rate Variability ◽

Autonomic Neuropathy ◽

Methylmalonic Acid ◽

Low Frequency ◽

Tissue Level ◽

Total Power ◽

Vitamin B ◽

Plasma Vitamin ◽

Functional Changes

Prevalence of vitamin B12 deficiency in the Indian population is not known, however; it is considered to be higher than in the Western population. Vitamin B12 deficiency is generally diagnosed by the plasma vitamin B12 level. Metabolites of vitamin B12 such as homocysteine (Hcy) and methylmalonic acid (MMA) are considered to be better markers to diagnose vitamin B12 deficiency at the tissue level. Autonomic neuropathy in vitamin B12 deficiency appears to precede other neurological signs. One of the recent techniques to evaluate autonomic neuropathy is heart rate variability (HRV). We evaluated 14 healthy young adults to explore the association of plasma vitamin B12, MMA, and Hcy levels with HRV. Resting lead II ECG was recorded and power spectral analyses were performed. Plasma MMA level was significantly and negatively correlated with the log-transformed low frequency (r = - 0.74, p = 0.002) and total power spectra (r = - 0.55, p = 0.03) of HRV in absolute units. Low frequency (LF) (r = - 0.56, p = 0.03) and high frequency (HF) (r = 0.57, p = 0.03), when represented in normalized units, were also correlated significantly with plasma MMA. In summary, plasma MMA but not vitamin B12 was significantly associated with HRV indices in a young adult population, suggesting that a tissue-level marker of vitamin B12 deficiency is more closely correlated with functional changes.

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Methylmalonyl-CoA mutase (EC 5.4.99.2) and methionine synthetase (EC 2.1.1.13) in the tissues of cobalt–vitamin B12 deficient sheep

British Journal Of Nutrition ◽

10.1079/bjn19900074 ◽

1990 ◽

Vol 64 (3) ◽

pp. 721-732 ◽

Cited By ~ 41

Author(s):

D. G. Kennedy ◽

A. Cannavan ◽

A. Molloy ◽

F. O' harte ◽

S. M. Taylor ◽

...

Keyword(s):

Spinal Cord ◽

Half Life ◽

Methylmalonic Acid ◽

Plasma Concentrations ◽

Vitamin B ◽

Synthetase Activity ◽

Liver And Kidney ◽

Brain And Spinal Cord ◽

Deficient Group ◽

Homocysteine Methyltransferase

The changes in the activities of the two vitamin B12-dependent enzymes methylmalonyl-CoA mutase (EC5.4.99.2) and methionine synthetase (5-methyltetrahydrofolate–homocysteine methyltransferase, EC 2.1.1.13) are described in two groups of sheep maintained for 20 weeks on either a cobalt-deficient or a Co-sufficient whole-barley diet. At the end of that period, the plasma concentrations of vitamin B12 were depressed and those of methylmalonic acid were raised in the Co-deficient group. During the course of the experiment hepatic holo-mutase activity, measured on biopsy samples, declined in Co-deficient animals with a half-life of 73 d. There was a similar, but slower decline in lymphocyte holo-mutase activity which fell with a half-life of 125 d. At slaughter, there was no difference between Co-sufficient and Co-deficient animals in total mutase activity in liver, kidney, brain and spinal cord. In contrast, the total-synthetase activity of liver and kidney was reduced by 60 and 30% respectively in the Co-deficient animals. There was no change in either group of animals in total-synthetase activity, or in either holo-mutase or holo-synthetase activity, in brain and spinal cord. In the Co-deficient animals, holo-mutase and holo-synthetase activities in liver, the tissue with the greatest activity of both enzymes, fell to 25 and 39% respectively, of that of Co-sufficient animals. The corresponding reductions for kidney were 12 and 51 % respectively. These results indicated that activity of both holoenzymes is greatly reduced in Co-deficient sheep.

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