THE GLUCOSE METABOLISM OF TRYPANOSOMA EVANSI AND THE ACTION OF TRYPANOCIDES

Abstract

It has long been recognized that trypanosomes are dependent on an adequate supply of glucose for the maintenance'of their metabolic processes (Yorke, Adams, and Murgatroyd, 1929;Geiger, Kligler, and Comaroff, 1930; von Brand, 1933). Later work has given some indication of the mechanism of the glucose metabolism of various species of the parasite, and the nature of the endpoints formed. Reiner and Smythe (1934) showed that the end-point of glucose metabolism in T. equiperdum was pyruvic acid, and the same group of workers (Reiner, Smythe, and Pedlow, 1936) showed that T. lewisi metabolized glucose more completely to yield formic, acetic and succinic acids, ethyl alcohol and carbon dioxide. Fulton and Stevens (1945) reported that the products of metabolism of T. rhodesiense were succinic, pyruvic, lactic, acetic and formic acids, glycerol, ethyl alcohol, and carbon dioxide.Regarding the respiratory activity of trypanosomes, Christophers and Fulton (1938) showed that oxygen consumption by T. rhodesiense was entirely dependent on the presence of glucose, and that 1 molecule of glucose required 1 molecule of oxygen. They also demonstrated the presence of dehydrogenase systems in trypanosome metabolism, and the absence of inhibition by cyanide. Reiner and Smythe (1934) reported that T. equiperdum produced very little carbon dioxide in the absence of bicarbonate, and that 1.80 molecules of acid (mostly pyruvic) were produced from the metabolism of 1 molecule of glucose. These workers also showed that trypanosomes could metabolize glycerol as well as glucose, but only under aerobic conditions. More recent work by Searle and Reiner (1940Reiner ( , 1941 Chen and Geiling (1946), has any direct evidence of glucose phosphorylation been demonstrated. These workers have shown that lysed trypanosomes will transform glucose to fructose-1,6-diphosphate and triose phosphates, and will oxidize phosphoglyceraldehyde to phosphoglyceric acid.The investigations described in this communication corroborate the findings of other workers regarding the respiratory activity of trypanosomes, and provide further evidence that glycolysis proceeds via the typical chain of phosphorylation reactions. Some preliminary indications are given of the points of attack-by trypanocidal agents, on which there are no previous reports. MATERIALS AND METHODSThe organism was a strain of Trypanosoma evansi isolated from a camel in the Sudan in 1938, and maintained in mice, in which it produces heavy, acute blood infections. Infected blood was-obtained from the exposed hearts of mice killed by placing them in an atmosphere of carbon dioxide.Respiration experiments.-Oxygen consumption was measured in conventional Warburg constant volume respirometers, using 15 ml. flasks maintained at 38' C.A set of twelve respirometers was run in duplicate, triplicate, or quadruplicate groups, according to the number of variants required. Since normal mouse blood showed only a negligible oxygen uptake, whole blood containing the trypanosomes was usually used, diluted with "isot...

The Use of Respiratory Inhibitors

“…The pyruvic oxidase system is heavily in hibited at 0.1 to 1.0 mM; excess glutathione (102), or slight excess of BAL2 (110) gives good protection. Other trivalent arsenicals have been employed and show similar proper ties (102,106,110,112,113). Disubstituted compounds, particularly di phenylchloroarsine, 4>As(Cl)4>, have been shown by Lotspeich & Peters (85) to inhibit isocitric dehydrogenase which is not inhibited by arsenite and lewisite.…”

Sensitivity of Trypanosomes to Metabolic Inhibitors*

“…Members of the vivax, congolense and lewisi-cruzi groups can metabolize glucose beyond the pyruvate stage,l3 but it i s commonly held that members of the bmcei group a r e unable to do s0. 13,[20][21][22] In this connection, it is interesting to note that homogenates of the bloodstream forms of T. rhodesienselg and T. equiperdum23 can reduce oxaloacetate to form malate in the presence of dihydronicotinamide adenine dinucleotide (NADH2) and…”

“…However, although several important classes of trypanocides a r e considered to act as inhibitors of carbohydrate metabolism, few definitive mechanistic studies have been undertaken in this area. 21,24 There is much evidence to indicate that the organometallic trypanocides (trivalent organic arsenicals and antimonials) a r e strong inhibitors of a number of sulfhydryl-rich glycolytic enzymes;2 however, only members of the brucei group a r e consistently highly sensitive to their action in vivo. 2,25 The relative refractoriness of other trypanosomal species could be due to a reduced ability of their analogous glycolytic enzymes to bind organometallic compounds.…”

“…13,[20][21][22] In this connection, it is interesting to note that homogenates of the bloodstream forms of T. rhodesienselg and T. equiperdum23 can reduce oxaloacetate to form malate in the presence of dihydronicotinamide adenine dinucleotide (NADH2) and can decarboxylate malate to form pyruvate in the presence of nicotinamide adenine dinucleotide phosphate (NADP). However, Ryleyl9 was unable to demonstrate C 0 2 fixation into pyruvate by bloodstream forms of T. rhodesiense.…”

“…However, although several important classes of trypanocides a r e considered to act as inhibitors of carbohydrate metabolism, few definitive mechanistic studies have been undertaken in this area. 21,24 There is much evidence to indicate that the organometallic trypanocides (trivalent organic arsenicals and antimonials) a r e strong inhibitors of a number of sulfhydryl-rich glycolytic enzymes;2 however, only members of the brucei group a r e consistently highly sensitive to their action in vivo.2,25 The relative refractoriness of other trypanosomal species could be due to a reduced ability of their analogous glycolytic enzymes to bind organometallic compounds. Differential sensitivity of phosphofructokinases of diverse origin to inhibition by trivalent organic antimonials has been demonstrated,26 and kinetic and immunologic differences were fOund27928 between analogous hexokinases and phosphoglucose isomerases of Schistosoma mansoni and its mammalian host.It has been suggested that the trypanocidal activity of the 5-nitrofurans 29,30 and the 8-aminoquinolines30 is related to their ability to function as electron-accepting redox intermediates, thereby interfering with the formation and/or utilization of nicotinamide adenine nucleotides intrypanosomal oxidative metabolism.…”