In summary, transsulphuration appears to be the most important pathway for the provision of Cys, particularly in situ in the skin. Therefore, factors affecting the uptake of Met by the skin and transsulphuration in the skin or in the wool follicles will play an important role in wool production. Synthesis of spermidine and spermine competes for Met with Cys synthesis, but polyamines are essential for cell division of the bulb. The quantitative relationship between wool growth and polyamines requires definition. In particular, there may be opportunities in genetic manipulation to increase spermidine concentration in the skin to change the rate of wool growth and fibre characteristics (Janne et al., 1999). Remethylation has little effect on overall Met catabolism in the skin. Little Met is lost through transamination. Therefore, the 'loss' of Met via its major catabolic pathways is actually essential for wool growth.
Although wool protein contains little Met, wool protein also accounts for less than 0.2 of the total protein synthesis in the skin (Adams et al., 2000). The rest, occurring in the root sheath, bulb cells and other non-follicle tissues in the skin requires a 'normal' level of Met. Wool growth could be maximized when Met is partitioned at appropriate proportions to protein, Cys and polyamine synthesis.
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