The effect of increasing methionine supply on the methionine conversion to cyst(e)ine in sheep

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Abstract
1. The conversion of methionine to cyst(e)ine was determined in sheep infused with different amounts of methionine (0-5 g/d) into the duodenum by assaying the incorporation of36S from intravenously-infused L-[35S]methionine into cyst(e)ine in wool, plasma albumin and the free plasma pool.2. The percentage of cystine-S in the plasma originating from methionine increased linearly from 4.5 to 18 with increasing supplemental methionine supply.3. The percentage of cysteine-S in albumin increased from 15 to 50; methionine supply increased to 3 g/d but then remained constant, indicating that the transsulphuration pathway of the liver was exceeded.4. The percentage of wool cysteine-S originating from methionine was high (∼ 70) at all methionine supplementation rates.