The immunological specificity of protein antigens has interesting aspects from the chemical viewpoint. Protein specificity appears to be closely associated with, and dependent on, chemical differences in the protein molecules. In most instances these differences are such that it is not possible to distinguish between similar proteins of different species by the usual methods of chemical investigation, but there are instances in which such a differentiation is possible by chemical or physical as well as by immunological tests. The differences which are responsible for serological specificity may not necessarily involve variations in the amount of certain special amino acids or even of free groups such as amino or carboxyl groups, but may be due merely to differences in the structural or spatial arrangement of certain groupings. A fundamental difference between antigenicity and specificity is indicated by the more recent work on complex antigens and haptens.There are several methods applicable to the study of the relationship between immunological specificity and the chemical properties of antigens; (a) alterations in the chemical constitution of the protein can be effected by various chemical processes such as oxidation, iodination, nitration, esterification, etc. (Obermayer and Pick (1), Landsteiner (2)), (b) a comparison can be made of the immunological properties of closely related vegetable proteins (Wells and Osborne (3)) or animal proteins (cf. review by Wells (4) pp. 68-74), and (c) compounds of well-defined chemical nature can be attached to the protein molecule (Landsteiner (5)). Each of these methods has a special
Evidence is available that suramin inhibits a few enzymes (for a review of the literature see Town, Wills, Wilson & Wormall, 1950). For reasons given in the preceding paper we have studied the action of very small amounts of the drug on a considerable number of enzymes under conditions as closely related as possible to the physiological. This paper is concerned mainly with experiments on non-proteolytic enzymes, with a few observations on the milk-clotting enzymes.The primary object of the experiments described here was to find out whether suramin, in amounts comparable with those which are sufficient to destroy trypanosomes in the blood and tissues of man and other animals, has any inhibitory effect on enzymes likely to be present in the trypanosome. Where marked enzyme inhibition occurs, a study has been made of the mechanism of the inhibition and the conditions under which the drug reacts with the enzyme. In view of the importance of carbohydrate for the nutrition of trypanosomes, special attention has been paid to those enzymes taking part in carbohydrate metabolism, i.e. the enzyme systems concerned with yeast fermentation and muscle metabolism. In this connexion it is of interest to note that Marshall (1948) has recently found that trivalent arsenicals and straight-chain diamidines inhibit certain enzyme systems concerned with carbohydrate metabolism in Trypanocmna evaris, and he has shown that the breakdown of glucose by trypanosomes follows almost exactly the pattern of glucose metabolism by yeast. EXPERIMENTAL Material8Urease. (a) Soya bean extract. Soya bean flour (British Drug Houses) (1 g.) was extracted with 95 ml. of water and the mixture centrifuged; the clear solution was mixed with 5 ml. of 0-2M-acetate buffer (pH 5-0) and centrifuged; the clear supernatant solution was used for the tests. (b) CrystaUine jack bean urease. This was prepared as described by Sumner & Somers (1947); a solution containing 9 mg. of protein/l. was used.Succinic oxida8e, 8uccinic dehydrogena8e and cytochrome oxida8e. The preparation of these enzyme systems from pig heart was carried out as described by Straub (1939) as far as the precipitation at pH 4-6. The precipitate was suspended in 5 vol. of 01 M-phosphate (pH 7.4) and 1 ml. of the mixture used for each test.Yeast juice. For different experiments baker's yeast, brewer's top yeast and brewer's bottom yeast were used. After it had been well washed with water, the yeast (100 g.) was mixed with kieselguhr (50 g.) and washed sand (100 g.), and the mixture ground to a dough in a heavy mechanical mortar. The dough was kept at room temperature for
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