A Study of the Proteins of the Wool Follicle

Abstract

SummaryA study has been made of the incorporation at different levels in the developing fibre of 35S into the two main protein fractions of wool. The proteins have been studied as the S-carboxymethyl derivatives rather than as the oxidized derivatives previously investigated. The results obtained give further support for a mechanism of synthesis which involves two stages. However, the incorporation of some 35S into the low-sulphur fraction of the keratinized fibre only 24 hr after the injection of [35S]cystine is somewhat surprising and possible explanations for this have been considered. A detailed comparison has been made of the proteins extracted from the unkeratinized portions of wool roots by 8M urea with those which can be extracted from the keratinized residue with urea-thioglycollate. As might be expected the latter proteins were very similar to those isolated from wool itself. The group of urea-soluble, high-sulphur proteins was different in containing considerable amounts of protein lower in both molecular weight and sulphur content than the comparable fraction from the fully keratinized wool. The possibility is discussed that some of these urea-soluble, high-sulphur proteins may be precursors of those in the fully keratinized fibre, conversion taking place by a process of sulphur enrichment.

The Growth and Composition of Wool IV. The Differential Response of Growth and of Sulphur Content of Wool to the Level of Sulphur-Containing Amino Acids given Per Abomasum

“…The only limitation to their synthesis may be an adequate supply of S-amino acids. This supports the two-stage theory of keratin synthesis in wool follicles, in which the high-sulphur proteins are the last formed (Downes, Sharry, and Rogers 1963;Downes et al 1966), and is consistent with the suggestion of Gillespie (1965) that the high-sulphur proteins of ex-keratins may be synthesized by the stepwise addition of sulphUi'-rich peptides to precursors. The results of this study do not support our earlier hypothesis (Reis and SchinckeI1964), namely that the synthesis of high-sulphur proteins may be the rate-limiting step in keratin synthesis.…”

Morphological and Protein Synthesis Changes in Skin during Wool Follicle Regeneration after Plucking and Mimosine Administration

“…Collagen and keratin fibres and large tissue fragments were removed by filtration through cloth and the homogenate was then centrifuged at 105000 g for 90 min. The supernatant solution was coIIected and the proteins reduced and alkylated as described by Downes et al (1966). The solution was dialysed exhaustively against distilled water at 4°C and lyophilized.…”

“…Protein extracts from fully keratinized wool were prepared as described by Downes et al (1966). For electrophoresis, the lyophilized samples were dissolved in 0·05 M tris-0'038 M glycine buffer (pH 8· 3) containing 8 M urea.…”

“…6 and containing 10M EDT A. This solution, which has proved very effective in earlier studies as a solvent for non-keratinized wool and hair proteins (Downes et al 1966), extracted approximately 20% of the protein and between 70 and 80 % of the radioactivity of skin slices. Polyacrylamide gel electrophoresis of the reduced and S-carboxymethylated proteins of a typical extract of normal sheep skin is shown in Fig.…”

A Search for a Simple Keratin?The Precursor Keratin Proteins From Cow's Lip Epidermis

“…It thus seems that the higher-sulphur fraction of the precursor keratin undergoes substantial changes in its passage to the stratum corneum. This picture could be complicated somewhat if there are cytoplasmic proteins in the precursor keratin which are withdrawn as the stratum corneum is approached (as suggested by Downes et al 1966) for the wool root system. However, the fact that the peptide map radioautographs are only concerned with peptides originally containing half-cystine residues indicates that this complication would probably be a minor one; furthermore, the fact that the amino acid composition of the whole extract (column 1, Table 1) is so similar to that ofPK.S2 does not indicate the presence of a substantial proportion of proteins other than keratins.…”