Studies on the inhibition of synthesis of the tyrosine-rich proteins of wool

Abstract

Three treatments known to produce weak wool were imposed on sheep, and the effects on the synthesis of high-tyrosine wool proteins were noted. The treatments were: intravenous infusion of the amino acid mimosine (a potential chemical defleecing agent), intravenous injection of the synthetic steroid Opticortenol (dexamethasone-21-trimethylacetate), and the abomasal infusion of methionine into sheep consuming a diet of wheat. All three treatments caused a partial suppression of hightyrosine protein synthesis. The inhibition caused by mimosine could not be prevented by the simultaneous infusion of tyrosine or phenylalanine, suggesting that in this system mimosine is not acting as a tyrosine antagonist. The role of phenylalanine in controlling the synthesis of the high-tyrosine proteins in wool was also investigated. Although the infusion of an amino acid mixture minus phenylalanine reduces the level of these proteins, supplements of phenylalanine or tyrosine do not stimulate their synthesis, irrespective of the initial level in the fibre. The importance of aromatic amino acids in the regulation of the high-tyrosine proteins is therefore uncertain. Suppression of the high-tyrosine proteins is usually accompanied by a stimulation in the synthesis of the ultra-high-sulphur proteins, although there does not seem to be a simple stoichiometric relationship between the two protein types. © 1975 ASEG.