Effects of phenylalanine and analogues of methionine and phenylalanine on the composition of wool and mouse hair.

Administration of the methionine analogue methoxinine (O-methyl-DL-homoserine) to sheep substantially changed the composition of wool; in addition wool fibres were weakened and the staple crimp frequency was reduced for a prolonged period. The proportions of high-tyrosine proteins were reduced by 40-45% whereas the high-sulfur proteins were usually slightly increased. The content of high-tyrosine proteins in wool was still depressed in most sheep 70 days after dosing with methoxinine. These experiments supported a previous finding that the cystine content of wool and its crimp frequency are not causally related. Ethionine, another methionine analogue, did not consistently change the composition of wool. In some sheep there was no change in the proportions of high-tyrosine proteins following administration of ethionine, even though weak wool was produced. This result, together with the lack of association between the content of high-tyrosine proteins and the strength of wool fibres in a sheep given methoxinine plus methionine, indicates that a reduction of the high-tyrosine proteins is not a prerequisite for the production of weak wool. Neither a threefold increase in the phenylalanine intake by mice nor the administration of three analogues of phenylalanine (4-fluoro-DL-phenylalanine, 4-chloro-DL-phenylalanine and beta-(2-thienyl)-DL-alanine) to sheep altered the composition of hair or wool. Fluorophenylalanine was incorporated into all the constituent proteins of wool to the extent of c. 2% of phenylalanine residues. The other analogues studied could not be detected in wool.