RELATIVE RESPONSES OF PROTEIN-TURNOVER IN 3 DIFFERENT SKELETAL-MUSCLES TO DIETARY LYSINE DEFICIENCY IN CHICKS

1. The effect of lysine deficiency was analysed on muscle protein turn over in 2-, 3- and 4-week-old growing broilers. Protein fractional syn thesis rates (FSR, in %/d) were measured by a reliable in vivo techniq ue (flooding dose of L-[4-H-3] phenylalanine) in the Pectoralis major (PM), the Anterior latissimus dorsi (ALD) and the Sartorius (SART) mus cles. Protein fractional breakdown rates (FBR, in %/d) were estimated as the difference between the synthesis rates and the growth rates of tissue protein. 2. Lysine deficiency resulted in significant increases in muscle FSR and FBR. When expressed in absolute rates (g/d), tissue protein deposition was reduced whatever the tissue. This phenomenon w as accompanied by decreased protein synthesis (ASR). 3. The protein tu rnover responsiveness to the lysine deficiency appeared to depend on t he studied muscle, since the PM muscle was the most sensitive whereas the SART and ALD muscles presented a lower sensitivity.