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Cobalt-Vitamin B-12 Deficiency Decreases Methionine Synthase Activity and Phospholipid Methylation in Sheep

D. Glenn Kennedy, W. John Blanchflower, John M. Scott, Donald G. Weir^**, Anne M. Molloy^**, Seamus Kennedy^* and Paul B. Young

Departments of Biochemistry ^* Departments of Pathology, Veterinary Sciences Division, Department of Agriculture for Northern Ireland, Stormont, Belfast BT4 3SD, Northern Ireland, United Kingdom Departments of Biochemistry ^** Departments of Clinical Medicine, Trinity College, Dublin, Ireland

Two groups of lambs were fed either a Co-deficient or a Co-sufficient whole barley-based diet for 28 wk to induce a severe Co-vitamin B-12 deficiency. Holo and apo methionine synthase activities were significantly lower in the liver, kidney and spinal cord of Co-deficient animals compared with controls. Neither form of this enzyme in the brain was affected by Co deficiency. The ratio of the tissue concentrations of S-adenosyl methionine to S-adenosyl homocysteine was significantly lower only in the liver of Co-deficient animals, suggesting that the activity of hepatic SAM-dependent methyltransferase enzymes would be impaired. Measurements of tissue concentrations of phosphatidyl choline and phosphatidyl ethanolamine revealed lower concentrations of phosphatidyl choline and a lower phosphatidyl choline:phosphatidyl ethanolamine ratio in both liver and brain of the Co-deficient animals. The latter finding occurred in the absence of changes in either methionine synthase activity or the methylation ratio and may result from impaired availability of hepatic phosphatidyl choline for transport into the brain.

KEY WORDS: • cobalt • vitamin B-12 • sheep • hypomethylation • phosphatidyl choline

Manuscript received 28 October 1991. Revision accepted 28 February 1992.

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