Effect of fasting and of methionine deficiency on L-methionine, DL-methionine and DL-2-hydroxy-4-methylthiobutanoic acid metabolism in broiler chicks

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Abstract
1. Metabolism of L-[1-14C]methionine, DL-[l-14C]methionine and DL-[ 1-14C]2-hydroxy-4-methylthiobutanoic acid (DL-HMB) by broiler chicks which had been fasted overnight or given a methionine-deficient diet was compared with fed (control) birds.2. The excretion of14C-labelled material, total14CO2exhaled,14C incorporation into tissue proteins and the14C-labelled material in perchloric-acid-soluble tissue fractions were measured 6 h after injection of the14C-labelled materials.3. The incorporation of14C into tissue proteins and the relative rates of conversion of D-methionine and DL-HMB to L-methionine in tissues under different nutritional regimens were compared using protein-bound14C:protein-free14C values.4. Fasted birds exhaled more14CO2than control birds but excreted less14C, while methionine-deficient birds behaved very similarly to the control animals in these respects.5. Fasted birds incorporated much less14C into proteins of tissues other than liver and kidney from all three labelled tracers. The values for protein-bound14C: protein-free14C were lower in all tissues.6. Methionine-deficient birds had similar levels of14C in tissue proteins but lower values for protein bound14C: protein-free14C.7. Examination of the values for protein-bound14C:protein-free14C suggest that brain and probably liver tissues from fasted and methionine-deficient birds showed improved rates of conversion of D-methionine and DL-HMB to L-methionine compared with control animals.