Studies on suramin. 9. The action of the drug on some enzymes

Abstract

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

The use of antagonists to characterize the receptors mediating depolarization of the rat isolated vagus nerve by α,β‐methylene adenosine 5′‐triphosphate

“…An interaction of cibacron blue and suramin with ATPase or GTPase enzymes important in either the transduction of purinoceptor-mediated responses or the metabolism of the agonist, could cause augmentation of responses to oj-methylene ATP (Wills & Wormall, 1950;Butler et al, 1988;Hourani & Chown, 1989). However, no definitive evidence to support any of these hypotheses was obtained in the present study and therefore the mechanism(s) underlying this phenomenon remains unclear.…”

Effects of the P2‐purinoceptor antagonist, suramin, on human platelet aggregation induced by adenosine 5′‐diphosphate

“…Suramin also selectively and competitively inhibits the effects of ATP on PC12 phaeochromocytoma cells with similar potency, the reported pA2 value being 4.52 (Nakazawa et al, 1990;Inoue et al, 1991). As well as antagonizing P2-purinoceptors, suramin is also known to inhibit a number of other proteins with nucleotide binding sites, for example yeast hexokinase (Wills & Wormall, 1950), erythrocyte membrane Na+/K+-ATPase (Fortes et al, 1973), firefly luciferase (Fortes et al, 1973), vacuole-type H+-ATPases (Moriyama & Nelson, 1988;Calcaterra et al, 1988), smooth muscle ectonucleotidases (Hourani & Chown, 1989), protein kinase C (Mahoney et al, 1990), mitochondrial adenine nucleotide exchanger (Calcaterra et al, 1988), the GTPase activity associated with Gi (Butler et al, 1988) and various polynucleotide synthesizing enzymes (Broder et al, 1985;Ono et al, 1988;Offensperger et al, 1988).…”

The electrical and mechanical responses of the rabbit saphenous artery to nerve stimulation and drugs

“…This may reflect the ability of the drug to inhibit ectonucleotidases responsible for the breakdown of ATP (Hourani & Chown, 1989). Suramin inhibited the effects of histamine and 5-HT perhaps as a result of the ability to bind a protein (Wills & Wormall, 1950) including those of receptor sites. While the responses to NA and KCI were unaffected by the drug, suramin seems insufficiently selective to be useful in the study of co-transmission in this tissue.…”