Rate of endogenous methionine oxidation in rats at different levels of methionine intake

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Abstract
1. The fractional rates of loss of 14C and body-weight were measured in growing female rats after a single dose of [1-14C]methionine. After the dose, the rats were maintained for 30 d on diets containing graded amounts of methionine and killed at 30 d.2. By 20 d after the dose the level of labelling of body proteins was fairly uniform. From 20 to 30 d, 14CO2 was collected at intervals. The rats were killed at 30 d and the total radioactivity remaining in the body was measured.3. The fractional loss of 14CO2 between days 20 and 30 was constant regardless of methionine intake except at the highest intake level.4. After correcting the fractional loss of 14CO2 for urinary 14C loss, a value of 35 mg/kg body-weight (20 mg/kg body-weight0·75) was obtained for the rate of endogenous methionine oxidation.