High-sulphur Proteins as a Major Cause of Variation in Sulphur Content between α-Keratins

Abstract

A COMMON feature of the wide variety of mammalian tissues classified as α-keratins is that they may be split into two separate protein fractions1–3 bearing a general resemblance to the ‘high-sulphur’ and ‘low-sulphur’ protein fractions first recognized in wool4,5. However, in these α-keratins which include hair, fur, wool, horn, nail, hoof, quill and baleen, the percentage of sulphur present varies greatly and covers the approximate range 2–6 per cent6–9 (Table 1). In general the horny keratins contain smaller amounts of sulphur than do the hairs and so the sulphur content of sheep horn, for example, is often lower than the sulphur content of wool from the same animal. It has been suggested7 that these differences in sulphur content can be used as a means of distinguishing keratins from one another, but in the case of wool it is now well established that there is a characteristic range of values of sulphur content (about 2.9–4.2 per cent) rather than a particular value for this keratin. A review of the relevant literature is given by Reis and Schinckel10,11. A sheep will produce wool with a high sulphur content during high levels of nutrition or during the abomasal infusion of sulphur-containing amino-acids; on the other hand, wool with a much lower sulphur content will be produced when the animal is on a copper-deficient or low-nutritional diet10–13. Moreover, these variations in the sulphur content of wool have been shown to originate primarily in the ‘high-sulphur’ proteins which change both in amount and in sulphur content1,14–16.