The Fate of Intradermal Doses of Labelled Amino Acids in Sheep

Abstract

SutrlllnaryWhen sheep were given intradermal doses of 0-5 ml of 0-9% NaCl containing 5-1400 p.g L_[36S]cystine, an area of labelled wool with a much higher specific activity than the rest of the fleece and corresponding to about 7 cm ll of skin was produced. Over this range of mass of cystine, about 21-1 % of the dose of 35S was incorporated into the wool grown by this area.When the 30 8 was injected intradermally as half-cystine residues bound to plasma proteins, a smaller proportion of the dose was incorporated than for similar masses of free cystine, but a larger area of skin (about 11 cro 2 ) produced wool of relatively high specific activity.L-[36S]cystine, Na 13 l!. and the -51Cr complex of ethylenediaminetetra-acetic acid ([51Cr]EDTA) all disappeared from the skin with a half-time of about 10 min, compared with about 10 hr for ovine [131I]albumin. The appearance of radioautograms of individual wool fibres labelled by repeated intradermal doses of L_[35S]cystine showed that the 3bS was incorporated into the growing fibres over a period of many days. It was concluded that there must be a "pool" of cystine, or of keratin precursors containing cystine, in the skin.Intradermal cystine all produced sufficient labelling of the wool fibres to enable rates of growth of individual fibres to be measured by the radioautographic technique. By using a HC-Iabelled amino acid a "permanent" timing mark can thus be imparted to growing wool fibres.After an intradermal dose of L.[3bS]methionine had been given, about 90% of the 35S incorporated into the wool at the injection site was present as cystine. Rougeot (1959) has shown that wool fibres from a small area of the skin of a sheep can be labelled with a subcutaneous dose of 1-10 fLc of ["S]cystine. The same fibres can be labelled repeatedly in this way, and their rates of growth can be accurately measured after the radioactive regions of the fibres have been revealed by radioautography. Fibres growing more than 2 cm from the point of injection show no detectable radioactivity. Rougeot chose [35S]cystine for several reasons, mainly based on the findings of Bern, Harkness, andBlair (1955) andof Ryder (1956): cystine makes up at least 10% of the wool keratin, the asS label rapidly appears in the follicle, only traces of the 35S appear in the wool or hair grown 3 weeks after the dose, and the half-life of asS, 87·1 days, enables the method to be used over periods of many months. ["S]cystine, given intravenously, was also used by Lyne (1959, 1961) in the development and application of a similar technique for the measurements of the rate of wool growth. INTRODUOTION

Metabolism of Cystine by Merino Sheep Genetically Different in Wool Production II. the Responses in Wool Growth to Abomasal Infusions of L-Cystine or Dl-Methionine

“…The results of indicated that daily abomasal infusions of 2·5 g DL-methionine increased the rate of entry of cystine into the body pool of cystine by approximately 60%. However, a greater proportion than this of the infused methionine may be available as cystine within the follicle, as extensive transulphuration of methionine in this tissue was demonstrated by Downes, Sharry, and Till (1964). Whether the specific influence of methionine on the rate of wool growth was exerted through one or more of its various functions as detailed by Reis (1967), or simply as an amino acid limiting for protein synthesis within the bulb of the follicle, remains uncertain.…”

A Survey of Methionine Adenosyltransferase and Cystathionine "g-Lyase Activities in Ruminant Tissues

“…Although Downes et al (1964) The present study was undertaken to survey the levels of two of the enzymes in the transsulphuration pathway in various tissues of a number of ruminant species. The two enzymes are the first one in the pathway, ATP : L-methionine S-adenosyltransferase (methionine adenosyltransferase, EC 2.5.1.6), and L-cystathionine cysteine-lyase (deaminating) [cystathionine y-lyase, EC 4.4.1.1; also formerly known as L-homoserine hydro-lyase (deaminating) (EC 4.2.1.15)].…”

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 increase in sulphur content of wool obtained during methionine infusions can be explained by conversion of at least some of the methionine to cysteine, as all the extra sulphur in wool grown during methionine infusions has been shown to be in the form of cyst(e)ine (Gillespie, Reis, and Schinckel 1964;Gillespie and Reis 1966). The conversion of methionine to cysteine and illcorporation of the cysteine into fibre keratin has been demonstrated in the guinea pig (De Bersaques 1964) and the sheep (Downes, Sharry, and Till 1964).…”