Giulivi 2008 Biochem J
|Giulivi C, Ross-Inta C, Horton AA, Luckhart S (2008) Metabolic pathways in Anopheles stephensi mitochondria. Biochem J 415:309-16.|
Abstract: No studies have been performed on the mitochondria of malaria vector mosquitoes. This information would be valuable in understanding mosquito aging and detoxification of insecticides, two parameters that have a significant impact on malaria parasite transmission in endemic regions. In the present study, we report the analyses of respiration and oxidative phosphorylation in mitochondria of cultured cells [ASE (Anopheles stephensi Mos. 43) cell line] from A. stephensi, a major vector of malaria in India, South-East Asia and parts of the Middle East. ASE cell mitochondria share many features in common with mammalian muscle mitochondria, despite the fact that these cells are of larval origin. However, two major differences with mammalian mitochondria were apparent. One, the glycerol-phosphate shuttle plays as major a role in NADH oxidation in ASE cell mitochondria as it does in insect muscle mitochondria. In contrast, mammalian white muscle mitochondria depend primarily on lactate dehydrogenase, whereas red muscle mitochondria depend on the malate-oxaloacetate shuttle. Two, ASE mitochondria were able to oxidize proline at a rate comparable with that of alpha-glycerophosphate. However, the proline pathway appeared to differ from the currently accepted pathway, in that oxoglutarate could be catabolized completely by the tricarboxylic acid cycle or via transamination, depending on the ATP need.
Labels: MiParea: Respiration, Comparative MiP;environmental MiP
Organism: Human, Rat, Birds, Hexapods Tissue;cell: Skeletal muscle Preparation: Isolated mitochondria
Coupling state: LEAK, OXPHOS Pathway: F, N, S, Gp, CIV, Other combinations, ROX
- Addition of malonate, an inhibitor of Complex II, caused a 90% inhibition of pyruvate oxidation, demonstrating that the tricarboxylic acid cycle is required for pyruvate oxidation. .. Some isolated mitochondria oxidize pyruvate without added primers by carboxylating pyruvate to malate or oxaloacetate. Two enzymes have been described that can catalyse this carboxylation: malic enzyme  and PC (pyruvate carboxylase) . .. Supplementation of mitochondria with malate yielded no significant increase in the rate of oxygen uptake in State 3 (Table 1) and, surprisingly, inhibited the response rate by 40%. These results suggested that, as observed in mammalian mitochondria, the transport of pyruvate and malate through the monocarboxylate–proton transporter and malate–citrate transporter respectively was also occurring in ASE mitochondria. However, the oxidation of malate to oxaloacetate proceeds through the enzymatic action of malate dehydrogenase in mammalian mitochondria, and because the Keq of this enzyme favours the formation of malate, oxaloacetate must be immediately removed by citrate synthase, a reaction that proceeds in the presence of acetyl-CoA formed from pyruvate via pyruvate dehydrogenase. The inhibition of malate oxidation by pyruvate addition in ASE mitochondria suggested a feedback inhibition of pyruvate onmalic enzyme, indicating that alternative carboxylation reactions to pyruvate oxidation were functional (e.g. via PC) and were similar to housefly sarcosomes. To confirm the involvement of malic enzyme, the effect of tartronic acid, an inhibitor of this enzyme, was tested on malate only or on malate- and pyruvate-supplemented mitochondria. Addition of tartronic acid resulted in 92% and 90% inhibition of State 3 oxygen uptake respectively. This result indicated that exogenously added malate efficiently provides oxaloacetate (through malate dehydrogenase), whereas pyruvate is provided via the anaplerotic reaction catalysed by malic enzyme.