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Methionine metabolism in isolated perfused livers from rats fed on zinc-deficient and restricted diets*

Published online by Cambridge University Press:  09 March 2007

John A. Duerre
Affiliation:
Department of Microbiology, Ireland Research Laboratory, University of North Dakota, Grand Forks, North Dakota 58202, USA
James C. Wallwork
Affiliation:
United States Department of Agriculture, Agricultural Research Service, Human Nutrition Research Center, Grand Forks, North Dakota, 58202, USA
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Abstract

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1. Sulphur amino acid metabolism in livers from rats which had been fed ad lib. on a restricted diet (malnourished) or a Zn-deficient diet was investigated. Perfusion of normal livers with different amounts of L-methionine revealed that homocysteine was recycled four to five times before being eliminated via the transsulphuration pathway.

2. From the perfusion experiments, we found no evidence that any of the enzymes involved in recycling homocysteine back to methionine (methylation pathway) were adversely effected by Zn deficiency or malnutrition.

3. The intracellular concentration of cystathionine and S-adenosylmethionine increased in all livers in response to increased concentrations of L-methionine (L-Met) in the perfusate.

4. The intracellular concentration of S-adenosylhomocysteine remained the same in all livers regardless of the concentration of perfusate methionine.

5. Although homocysteine did not accumulate in the cell, it was excreted into the perfusate. The amount of homocysteine in the perfusate of livers from Zn-deficient rats was higher than either ad lib. or pair-fed rats.

6. The breakdown of homocysteine, via the transsulphuration pathway, was augmented by Zn deficiency. This was apparent from the greater amount of α-ketobutyrate excreted by livers from Zn-deficient rats compared with pair-fed or ad lib.-fed controls.

7. The increase in metabolism of L-Met, via the transsulphuration pathway, in the livers from Zn-deficient rats appears to reflect the lack of demand for this compound in protein synthesis and methylation reactions (Wallwork & Duerre, 1985).

Type
Papers on General Nutrition
Copyright
Copyright © The Nutrition Society 1986

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