On the Biochemistry of Skin, and the Chemical Basis of Skin Swelling.
IN previous investigations by the authors [1924] it has been shown that the swelling of a fibrous tissue, such as skin, depends on both structural and chemical factors. The chemical factors considered were those due to variation in the external swelling medium. There remain those contributed by the skin itself. The influence of these is well shown by comparing the swelling of fresh goat skin with that of commercial sun-dried goat skin. The drying of the skin at a tropical temperature has caused a chemical change in its proteins which is made visible by the firm cementing together of the fibrils of the fibres. Skin is composed chiefly of proteins, though it contains in addition fats, sterols, and sterol esters. Rosenthal [1916] gives the following analysis of calf skin dried in vacuo at 55-60°.
The swelling of structured proteins - The influence of the reticular tissue on the swelling of collagen in water and hydrochloric acid
Previous observations on the swelling of fibrous tissues and fibres (Kaye and Jordan-Lloyd, 1924, a ; Marriott, 1932; Jordan-Lloyd, Marriott, and Pleass, 1933; Jordan-Lloyd and Marriott, 1933, 1934) have shown that the swelling of biological material is largely influenced by its structure. Even a fibre that is histologically structureless, as, for example, a fibre of silk-fibroin (silk-gut), can be shown to consist of a number of fine fibrils held together by lateral cohesive forces. Both with silk fibres and keratin fibres (horsehair), the evidence suggests that the structure of the fibre is maintained by what may be described as an equivalent of a system of internal girders, these girders being the lateral cohesive forces between the molecules. Keratin fibres (hairs) are of cellular origin, though a fibrous rather than a cellular structure exists in the hair shaft. Collagen fibres are also of cellular origin, though in their fully developed form they are by no means such rigid structures as silk fibres or hairs, and swell much more freely. It has been shown already that the swelling of collagen fibres, while woven together to form the tissue of the skin, depends both on the structure of the fibres and on the pattern of the weave, skin pieces where the weave is loose swelling more freely under the same conditions than skin pieces where the weave is more compact (Kaye and Jordan-Lloyd, 1924). Moreover, it has also been shown that if the fibres were invested with a film of coagulated protein, swelling was less than under fresh conditions. Swelling is, therefore, also a function of the external stresses exerted on the fibre, a generalization confirmed by Marriott (1932) in a study of the behaviour of single collagen fibre bundles teased out of the skin tissue. Collagen fibres cannot be obtained free from all other tissues. They are invested and held together throughout the skin by another fibrous protein, the reticular tissue (Kaye, 1929; Kuntzel and Prakke, 1933). This tissue forms the equivalent of a system of external girders round the actual collagen fibres and influences their behaviour. Collagen fibres from skin which were used in the earlier work are not a suitable material for the study of the influence of the reticular tissue on the swelling of collagen owing to the difficulty of teasing out a good supply of undamaged, suitable single fibres in a reasonably short space of time from fresh skin. For this reason the tendons from rats’ tails were selected for study. Previous work on the swelling of tendons has been recorded by Kuntzel (1926) and of their structure by Kuntzel and Prakke (1933).
On the fractionation of β-lactoglobulin and α-lactalbumin
Abstract Existing methods for the preparation of α-lactalbumin and β-lactoglobulin are examined critically. It is proposed that the most satisfactory method for the preparation of the whey protein fraction from bovine milk is (NH 4 ) 2 SO 4 fractionation. A number of new gentle procedures for the fractionation of the whey proteins are compared with some existing methods. The distribution of total protein at various stages is determined by total Kjeldahl nitrogen and the kind of protein by starch-gel electrophoresis. The effect of variables, such as pH, salt concentration and temperature on the separation of α-lactalbumin and serum albumin from β-lactoglobulin is studied. Differences in the behavior ( e.g. solubility) of genetic variants of β-lactoglobulin are noted. The solubility of each of the major whey proteins, under similar conditions to those used in the fractionation, is compared with its solubility in the whey protein mixture. The understanding gained of factors important in the fractionation is used in recommending new procedures for α-lactalbumin and β-lactoglobulin isolation.