It has been shown (Fraser & MacRae, 1963) that solutions of unfractionated feather-keratin derivatives can be dried down into films that give welloriented X-ray-diffraction patterns containing many of the features associated with the microfibrillar structure of the native material. It was found that similar films could be obtained from the fractions described by . In most cases spontaneous birefringence developed around the edge of the film during drying. The X-ray-diffraction patterns yielded by these films when the X-ray beam passed parallel to the surface were similar to those of the unfractionated derivatives at low angles of diffraction, with a prominent meridional reflexion at 23A and equatorial reflexion at 33A. At wider angles the fractionated materials show strong layer lines at 4*8 and 2-4k and a series of equatorials which index as orders of a 33i spacing.The electron micrographs shown in Plate 1 were obtained by spraying a 1:1 (v/v) mixture of 0 05 % protein solution and 1 % phosphotungstate, pH 5 6, on to grids covered with a carbon-collodion fihm and using the negative-staining method of Brenner & Horne (1959). It is apparent from Plate 1 that, on drying, the fractionated derivatives spontaneously polymerize to form fibrils. The apparent thickness of the fibrils varies from 40 to 60 A at their narrowest part (arrow in Plate 1 b) to approx. 130A at their widest part, suggesting that they are helical with a pitch of approx. 1500 k. At first sight the fibrils appear to consist of two filaments coiled around each other to give a two-strand rope, but a ribbon containing three strands cannot be excluded at present. A feature is the tendency of the fibrils to aggregate laterally in precise register.

G. A. JACOBY 1964 2. There is a lag in growth and oxygen uptake on transferring cells from growth on glucose to an amino acid medium during which the enzymes for amino acid catabolism are formed. 3. In the presence of glucose, or any of a variety of alternative energy sources, adaptation for amino 'acid breakdown is repressed. 4. The effect of glucose on the induction of individual enzymes in the catabolic pathways of tyrosine and histidine has been measured with cellfree extracts. 5. p-Hydroxyphenylpyruvate hydroxylase and homogentisate oxygenase, the second and third enzymes of tyrosine degradation, are repressed by glucose, but tyrosine transaminase, the first enzyme, is neither induced by tyrosine nor repressed by glucose. 6. Histidase and urocanase, the first enzymes in the histidine pathway, are repressed by glucose. 7. Utilization of tyrosine or histidine by fully adapted cells is not decreased in the presence of glucose or other metabolic repressors except acetate. 8. Induction and repression of amino acid oxidation are complementary control mechanisms by which the large enzymic potential of this organism is regulated. I am indebted to Dr J. Mandelstam for valuable criticism and advice. This investigation was supported by a U.S. Public Health Service fellowship (no. EPD-18 124) from the National Institute of Allergy and Infectious Diseases. we have found that 8m-urea is not necessary for solution of the protein. The percentage of protein dissolved was determined from the dry weights of the washed residues. Studies on the effect of temperature on the rate of solution gave results almost identical with the first method, i.e. an activation energy of about 13 kcal./mole. The procedure adopted to prepare soluble proteins was as follows: two solutions, containing (i) CuSO4 (01M) plus NH3 (0-5N), Vol. 92 9

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SummaryA study has been made on the extraction of reduced protein from wool by two methods. In one the aim has been to solubilize as much protein as possible and in the other to use the mildest conditions possible. In the first method extraction was made with potassium thioglycollate in the presence of urea and the variables temperature, pH, urea concentration, and thioglycollate concentration were studied. It was found that between 80 and 85% of wool can be solubilized at room temperature by 0-2M potassium thioglycollate at pH 10-5 in the presence of 6M urea. In the second method a total of more than 60% of the wool was solubilized; the highsulphur protein was first preferentially extracted by O· 8M potassium thioglycollate at pH 10'5 and O°C, and low-sulphur protein then released from the residue by plasmolysis by immersing the residue in ice-cold distilled water. The advantage of this method is that at no time does the temperature rise above O°C or the pH above 10-5.Although the low-sulphur proteins (i.e. proteins precipitable at pH 4·4 after alkylation with iodoacetate) prepared by both these procedures gave essentially single-boundaried patterns on electrophoresis at pH 11-0, amino acid analyses indicated that, in addition to the SCMKAI and SCMKA2 proteins previously reported, these proteins also contain variable amounts of constituents rich in glycine and S-carboxymethyl cysteine.

SummaryA study has been made of the incorporation at different levels in the developing fibre of 35S into the two main protein fractions of wool. The proteins have been studied as the S-carboxymethyl derivatives rather than as the oxidized derivatives previously investigated. The results obtained give further support for a mechanism of synthesis which involves two stages. However, the incorporation of some 35S into the low-sulphur fraction of the keratinized fibre only 24 hr after the injection of [35S]cystine is somewhat surprising and possible explanations for this have been considered. A detailed comparison has been made of the proteins extracted from the unkeratinized portions of wool roots by 8M urea with those which can be extracted from the keratinized residue with urea-thioglycollate. As might be expected the latter proteins were very similar to those isolated from wool itself. The group of urea-soluble, high-sulphur proteins was different in containing considerable amounts of protein lower in both molecular weight and sulphur content than the comparable fraction from the fully keratinized wool. The possibility is discussed that some of these urea-soluble, high-sulphur proteins may be precursors of those in the fully keratinized fibre, conversion taking place by a process of sulphur enrichment.