Characterization of Transport Systems for Cysteine, Lysine, Alanine, and Leucine in Wool Follicles of Sheep

The study investigated the uptake of amino acids (AA) cysteine (Cys), leucine (Leu), alanine (Ala), and lysine (Lys) into wool follicles of sheep using a short-term culture of sheep skin strips. It was found that these AAs are incorporated into different regions of the follicle, reflecting their roles in fiber production. Cysteine was primarily taken up in the keratinization zone, lysine in the germinative cells and inner root sheath, while leucine and alanine were incorporated in multiple areas including the follicle bulb and keratinizing fiber. The uptake rates for these AAs were highest for Cys, followed by Leu, Ala, and Lys. Cysteine uptake was carrier-mediated, following Michaelis-Menten kinetics, and mostly Na-independent, suggesting a unique transport system in the follicle. Alanine transport was consistent with system A, leucine uptake suggested a variant of system L, and lysine uptake was in line with the typical system y+. The study suggests that diets for optimal wool growth should match the AA uptake rates observed, and genetic variations in AA transport proteins could influence wool growth among different sheep genotypes.