Utilisation of free and protein dietary lysine in chicks estimated with isotopes

Abstract

1. Utilisation of supplementary free L‐lysine hydrochloride was estimated in growing chicks and compared to that of protein‐bound lysine. The technique used is based on the oxidative catabolism of either free (U— ¹⁴C)‐L‐lysine or the labelled lysine incorporated into yeast proteins.

2. The animals received a wheat‐wheat gluten diet which was L‐lysine‐supplemented with either unlabelled yeast proteins or a mixture of synthetic amino acids simulating the yeast proteins or L‐lysine hydro‐chloride alone.

3. At 13 and 15 days after hatching, expiry of (¹⁴C) — carbon dioxide was followed 8 h after dosing with the appropriate radiolabelled diet. After 4 h, 0.66% of the protein‐bound and 5.3 to 5.7% of the free lysine radioactivity appeared as ¹⁴C‐ carbon dioxide.

4. It is concluded that under these conditions lysine from both sources was utilised more efficiently than had been assumed hitherto, protein‐bound lysine being slightly better utilised than free lysine.

Notes

Present address: Humboldt‐University Berlin, Department of Microbiology, 1017 Berlin, GDR.