Wool follicles are potentially able to synthesize specific high.sulphur proteins in which about 30% of the amino acid residues are half-cystine (Gillespie and Reis 1966). The amount of these proteins incorporated into the fibre is related to the availability of sulphur-containing amino acids for metabolism in the sheep. There is a linear relation between the sulphur content of a wool fibre and its content of these proteins (Broad, Gillespie, and Reis 1970).

When the diet of sheep is supplemented by the infusion of sulphur-containing amino acids or casein into the abomasum, the newly synthesized wool shows characteristic changes in its amino acid composition, with significant increases in cystine, proline and serine and decreases in aspartic acid and phenylalanine. This modification seems to be due entirely to an alteration in the overall composition of the high-sulphur proteins and to an increase in their proportion in the fibre. These variations are not the result of a change in the composition of individual proteins, but are due to alterations in their relative proportions and to the initiation of the synthesis of ;new' proteins, many of which are extremely rich in cystine. It is suggested that the heterogeneity of the high-sulphur proteins may be due, in part, to similar changes in composition caused by natural variations in the nutrition of sheep.

The sulphur content of wool can vary within the range of about 2·7-4·2% depending on the diet of the sheep. The lower limit may represent a limiting fundamental structure for wool as it has not been possible to produce wool of sulphur content lower than 2·7% during sulphur-deprivation experiments. There is a highly significant linear relationship between the sulphur content of wool and its content of high-sulphur proteins. The major part of this variation in sulphur content is due to alterations in the extent of biosynthesis of proteins of extremely high sulphur content having about one-third of the amino acid residues presen1, as half cystine. The biosynthesis of these proteins may be under separate metabolic control for they can be produced at maximum rate under conditions where the synthesis of other highsulphur proteins is partly inhibited by a sulphur-deficient diet or by high levels of DL-methionine supplementation

1. An enzyme produced by Aeromonas hydrophila and capable of lysing Staphylococcus aureus cells was purified 180-fold by gel filtration and chromatography on columns of AG-50 W resin. 2. Physical measurements on the purified enzyme suggest that it is a small basic protein with an isoelectric point between pH9.0 and pH9.5. 3. Maximum lytic activity was obtained in 20mm-tris-glycine buffer, pH8.5, at 45 degrees , with no detectable activity in the absence of a nitrogenous base. 4. The enzyme is active in the above buffer containing 1.5m-sucrose, and is useful for the preparation of protoplasts of Staphylococcus aureus. 5. Purified cell wall peptidoglycans of two strains of Staphylococcus aureus, differing in amino acid composition, were hydrolysed by the enzyme with the liberation of glycine oligopeptides, principally diglycine and triglycine. 6. Synthetic glycine oligopeptides larger than triglycine, but not polyglycine, were hydrolysed, as were a number of leucine-containing dipeptides and tripeptides, but no proteolytic activity could be demonstrated. 7. It is concluded that the enzyme is lytic towards Staphylococcus aureus because it splits the pentaglycine cross-links of the cell-wall peptidoglycan.