Oxidation of proline by sarcosomes of the tsetse fly, Glossina morsitans

Endosymbiont-derived metabolites are essential for tick host reproductive fitness

Ticks, like other obligatory blood-feeding arthropods, rely on endosymbiotic bacteria to supplement their diet with B vitamins lacking in blood. It has been suggested that additional metabolites such as L-proline may be involved in this nutritional symbiosis, but this has yet to be tested. Here, we studied the metabolite-based interaction between the brown dog tick Rhipicephalus sanguineus (Acari: Ixodidae) and its Coxiella-like endosymbionts (CLE). We measured amino acid titers and tested the effect of B vitamins and L-proline supplementation on the fitness of CLE-suppressed female ticks, displaying low titers of CLE. We found higher titers of L-proline in the symbiont-hosting organs of unfed ticks and in engorged blood-fed whole ticks. Supplementation of B vitamins increased the hatching rate of CLE-suppressed ticks; this effect appears to be stronger when L-proline is added. Our results indicate that L-proline is produced by CLE, and we suggest that CLE is essential in states of high metabolic demand that affects tick reproductive fitness, such as oogenesis and embryonic development. These findings demonstrate the broader effect of nutritional symbionts on their hosts and may potentially contribute to the control of ticks and tick-borne diseases.

IMPORTANCE

Coxiella-like endosymbionts (CLE) are essential to the brown dog tick Rhipicephalus sanguineus for feeding and reproduction. This symbiosis is based on the supplementation of B vitamins lacking in the blood diet. The involvement of additional metabolites has been suggested, but no experimental evidence is available as yet to confirm a metabolic interaction. Here, we show that B vitamins and L-proline, both of which contribute to tick reproductive fitness, are produced by CLE. These findings demonstrate the importance of symbiont-derived metabolites for the host's persistence and shed light on the complex bacteria-host metabolic interaction, which can be channeled to manipulate and control tick populations.

Adaptive changes in energy reserves and effects of body melanization on thermal tolerance in Drosophila simulans

Seasonally polyphenic types have been documented in many Drosophilids, which differ significantly during thermal stress. Although Drosophila simulans is a sibling species to Drosophila melanogaster, both thrive in the temperate and tropical climates, but various climatic factors are expected to impact their distribution and abundance. As a result, D. simulans may use phenotypic plasticity to adapt to colder and drier circumstances in temperate zones, although such studies are less known. In the present study, our main aim was to find a link between adaptive plasticity and thermal tolerance in D. simulans. We characterized two morphs in D. simulans flies based on the abdominal melanization collected from the same locality and season, as this trait is highly associated with the larval developmental conditions. Our results suggested that flies reared from dark and light morph showed significant differences in the basal level of proline, carbohydrates (trehalose, glycogen), and lipids (cuticular lipids and total body lipids) within simulated seasons and morph lineages in D. simulans flies. We further showed that D. simulans reared from dark morph are better adapted to cold conditions, whereas light flies are more adapted to warm conditions. The flies, both from light and dark morph lineages, when reared at 15 °C, showed an increase in the level of total body lipids after acclimation at 0 °C but a decrease in the level of proline and carbohydrates (trehalose, glycogen). Heat acclimation increases glycogen levels in the flies from light morph lineage while decreases trehalose and proline.

Cytochrome c Oxidase at Full Thrust: Regulation and Biological Consequences to Flying Insects

Flight dispersal represents a key aspect of the evolutionary and ecological success of insects, allowing escape from predators, mating, and colonization of new niches. The huge energy demand posed by flight activity is essentially met by oxidative phosphorylation (OXPHOS) in flight muscle mitochondria. In insects, mitochondrial ATP supply and oxidant production are regulated by several factors, including the energy demand exerted by changes in adenylate balance. Indeed, adenylate directly regulates OXPHOS by targeting both chemiosmotic ATP production and the activities of specific mitochondrial enzymes. In several organisms, cytochrome c oxidase (COX) is regulated at transcriptional, post-translational, and allosteric levels, impacting mitochondrial energy metabolism, and redox balance. This review will present the concepts on how COX function contributes to flying insect biology, focusing on the existing examples in the literature where its structure and activity are regulated not only by physiological and environmental factors but also how changes in its activity impacts insect biology. We also performed in silico sequence analyses and determined the structure models of three COX subunits (IV, VIa, and VIc) from different insect species to compare with mammalian orthologs. We observed that the sequences and structure models of COXIV, COXVIa, and COXVIc were quite similar to their mammalian counterparts. Remarkably, specific substitutions to phosphomimetic amino acids at critical phosphorylation sites emerge as hallmarks on insect COX sequences, suggesting a new regulatory mechanism of COX activity. Therefore, by providing a physiological and bioenergetic framework of COX regulation in such metabolically extreme models, we hope to expand the knowledge of this critical enzyme complex and the potential consequences for insect dispersal.

A Tale of Three Species: Adaptation of Sodalis glossinidius to Tsetse Biology, Wigglesworthia Metabolism, and Host Diet

The tsetse fly is the insect vector for the Trypanosoma brucei parasite, the causative agent of human African trypanosomiasis. The colonization and spread of the trypanosome correlate positively with the presence of a secondary symbiotic bacterium, Sodalis glossinidius The metabolic requirements and interactions of the bacterium with its host are poorly understood, and herein we describe a metabolic model of S. glossinidius metabolism. The model enabled the design and experimental verification of a defined medium that supports S. glossinidius growth ex vivo This has been used subsequently to analyze in vitro aspects of S. glossinidius metabolism, revealing multiple unique adaptations of the symbiont to its environment. Continued dependence on a sugar, and the importance of the chitin monomer N-acetyl-d-glucosamine as a carbon and energy source, suggests adaptation to host-derived molecules. Adaptation to the amino acid-rich blood diet is revealed by a strong dependence on l-glutamate as a source of carbon and nitrogen and by the ability to rescue a predicted l-arginine auxotrophy. Finally, the selective loss of thiamine biosynthesis, a vitamin provided to the host by the primary symbiont Wigglesworthia glossinidia, reveals an intersymbiont dependence. The reductive evolution of S. glossinidius to exploit environmentally derived metabolites has resulted in multiple weaknesses in the metabolic network. These weaknesses may become targets for reagents that inhibit S. glossinidius growth and aid the reduction of trypanosomal transmission.IMPORTANCE Human African trypanosomiasis is caused by the Trypanosoma brucei parasite. The tsetse fly vector is of interest for its potential to prevent disease spread, as it is essential for T. brucei life cycle progression and transmission. The tsetse's mutualistic endosymbiont Sodalis glossinidius has a link to trypanosome establishment, providing a disease control target. Here, we describe a new, experimentally verified model of S. glossinidius metabolism. This model has enabled the development of a defined growth medium that was used successfully to test aspects of S. glossinidius metabolism. We present S. glossinidius as uniquely adapted to life in the tsetse, through its reliance on the blood diet and host-derived sugars. Additionally, S. glossinidius has adapted to the tsetse's obligate symbiont Wigglesworthia glossinidia by scavenging a vitamin it produces for the insect. This work highlights the use of metabolic modeling to design defined growth media for symbiotic bacteria and may provide novel inhibitory targets to block trypanosome transmission.

ATP-driven and AMPK-independent autophagy in an early branching eukaryotic parasite

Autophagy is a catabolic cellular process required to maintain protein synthesis, energy production and other essential activities in starved cells. While the exact nutrient sensor(s) is yet to be identified, deprivation of amino acids, glucose, growth factor and other nutrients can serve as metabolic stimuli to initiate autophagy in higher eukaryotes. In the early-branching unicellular parasite Trypanosoma brucei, which can proliferate as procyclic form (PCF) in the tsetse fly or as bloodstream form (BSF) in animal hosts, autophagy is robustly triggered by amino acid deficiency but not by glucose depletion. Taking advantage of the clearly defined adenosine triphosphate (ATP) production pathways in T. brucei, we have shown that autophagic activity depends on the levels of cellular ATP production, using either glucose or proline as a carbon source. While autophagosome formation positively correlates with cellular ATP levels; perturbation of ATP production by removing carbon sources or genetic silencing of enzymes involved in ATP generation pathways, also inhibited autophagy. This obligate energy dependence and the lack of glucose starvation-induced autophagy in T. brucei may reflect an adaptation to its specialized, parasitic life style.

Cold and desiccation stress induced changes in the accumulation and utilization of proline and trehalose in seasonal populations of Drosophila immigrans

Changes in the levels of energy metabolites can limit survival ability of Drosophila species under stressful conditions but this aspect has received less attention in wild populations collected in different seasons. We tested cold or desiccation triggered changes in the accumulation or utilization of two energy metabolites (trehalose and proline) in Drosophila immigrans flies reared under season specific environmental conditions. Such D.immigrans populations were subjected to different durations of cold (0°C) or desiccation stress (5% RH) or dual stress. We found stress induced effects of cold vs desiccation on the levels of trehalose as well as for proline. Different durations of cold stress led to accumulation of trehalose while desiccation stress durations revealed utilization of trehalose. In contrast, there was accumulation of proline under desiccation and utilization of proline with cold stress. Since accumulation levels were higher than utilization of each energy metabolite, the effects of dual stress showed additive effect. However, there was no utilization of total body lipids under cold or desiccation stress. We observed significant season specific differences in the amount of energy metabolites but the rate of metabolism did not vary across seasons. Stress triggered changes in trehalose and proline suggest possible link between desiccation and cold tolerance. Finally, stress specific (cold or desiccation) compensatory changes in the levels of trehalose and proline suggest possible energetic homeostasis in D.immigrans living under harsh climatic conditions of montane localities.

Sources of superoxide/H2O2 during mitochondrial proline oxidation

p53 Inducible gene 6 (PIG6) encodes mitochondrial proline dehydrogenase (PRODH) and is up-regulated several fold upon p53 activation. Proline dehydrogenase is proposed to generate radicals that contribute to cancer cell apoptosis. However, there are at least 10 mitochondrial sites that can produce superoxide and/or H₂O₂, and it is unclear whether proline dehydrogenase generates these species directly, or instead drives production by other sites. Amongst six cancer cell lines, ZR75-30 human breast cancer cells had the highest basal proline dehydrogenase levels, and mitochondria isolated from ZR75-30 cells consumed oxygen and produced H₂O₂ with proline as sole substrate. Insects use proline oxidation to fuel flight, and mitochondria isolated from Drosophila melanogaster were even more active with proline as sole substrate than ZR75-30 mitochondria. Using mitochondria from these two models we identified the sites involved in formation of superoxide/H₂O₂ during proline oxidation. In mitochondria from Drosophila the main sites were respiratory complexes I and II. In mitochondria from ZR75-30 breast cancer cells the main sites were complex I and the oxoglutarate dehydrogenase complex. Even with combinations of substrates and respiratory chain inhibitors designed to minimize the contributions of other sites and maximize any superoxide/H₂O₂ production from proline dehydrogenase itself, there was no significant direct contribution of proline dehydrogenase to the observed H₂O₂ production. Thus proline oxidation by proline dehydrogenase drives superoxide/H₂O₂ production, but it does so mainly or exclusively by providing anaplerotic carbon for other mitochondrial dehydrogenases and not by producing superoxide/H₂O₂ directly.

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Proline dehydrogenase is thought to produce reactive oxygen species (ROS) in cancer cells and to promote apoptosis.

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Isolated mitochondria from Drosophila melanogaster and from a human breast cancer cell line oxidize proline producing superoxide/H₂O₂ at measurable rates.

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Proline oxidation drives superoxide/H₂O₂ production indirectly at other sites and it is unlikely that proline dehydrogenase produces superoxide/H₂O₂ itself.

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In Drosophila, superoxide/H₂O₂ arises from sites I_F and II_F (the flavin sites from complexes I and II, respectively).

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In the breast cancer cell line the main sites are I_F and O_F (from the oxoglutarate dehydrogenase complex).

Mitochondrial NAD+-dependent malic enzyme from Anopheles stephensi: a possible novel target for malaria mosquito control

Background

Anopheles stephensi mitochondrial malic enzyme (ME) emerged as having a relevant role in the provision of pyruvate for the Krebs' cycle because inhibition of this enzyme results in the complete abrogation of oxygen uptake by mitochondria. Therefore, the identification of ME in mitochondria from immortalized A. stephensi (ASE) cells and the investigation of the stereoselectivity of malate analogues are relevant in understanding the physiological role of ME in cells of this important malaria parasite vector and its potential as a possible novel target for insecticide development.

Methods

To characterize the mitochondrial ME from immortalized ASE cells (Mos. 43; ASE), mass spectrometry analyses of trypsin fragments of ME, genomic sequence analysis and biochemical assays were performed to identify the enzyme and evaluate its activity in terms of cofactor dependency and inhibitor preference.

Results

The encoding gene sequence and primary sequences of several peptides from mitochondrial ME were found to be highly homologous to the mitochondrial ME from Anopheles gambiae (98%) and 59% homologous to the mitochondrial NADP⁺-dependent ME isoform from Homo sapiens. Measurements of ME activity in mosquito mitochondria isolated from ASE cells showed that (i) V_max with NAD⁺ was 3-fold higher than that with NADP⁺, (ii) addition of Mg²⁺ or Mn²⁺ increased the V_max by 9- to 21-fold, with Mn²⁺ 2.3-fold more effective than Mg²⁺, (iii) succinate and fumarate increased the activity by 2- and 5-fold, respectively, at sub-saturating concentrations of malate, (iv) among the analogs of L-malate tested as inhibitors of the NAD⁺-dependent ME catalyzed reaction, small (2- to 3-carbons) organic diacids carrying a 2-hydroxyl/keto group behaved as the most potent inhibitors of ME activity (e.g., oxaloacetate, tartronic acid and oxalate).

Conclusions

The biochemical characterization of Anopheles stephensi ME is of critical relevance given its important role in bioenergetics, suggesting that it is a suitable target for insecticide development.

LGH, Welch KC. The sugar oxidation cascade: aerial refueling in hummingbirds and nectar bats

Most hummingbirds and some species of nectar bats hover while feeding on floral nectar. While doing so, they achieve some of the highest mass-specific values among vertebrates. This is made possible by enhanced functional capacities of various elements of the ‘O2 transport cascade’, the pathway of O2 from the external environment to muscle mitochondria. Fasted hummingbirds and nectar bats fly with respiratory quotients (RQs; ) of ∼0.7, indicating that fat fuels flight in the fasted state. During repeated hover-feeding on dietary sugar, RQ values progressively climb to ∼1.0, indicating a shift from fat to carbohydrate oxidation. Stable carbon isotope experiments reveal that recently ingested sugar directly fuels ∼80 and 95% of energy metabolism in hover-feeding nectar bats and hummingbirds, respectively. We name the pathway of carbon flux from flowers, through digestive and cardiovascular systems, muscle membranes and into mitochondria the ‘sugar oxidation cascade’. O2 and sugar oxidation cascades operate in parallel and converge in muscle mitochondria. Foraging behavior that favours the oxidation of dietary sugar avoids the inefficiency of synthesizing fat from sugar and breaking down fat to fuel foraging. Sugar oxidation yields a higher P/O ratio (ATP made per O atom consumed) than fat oxidation, thus requiring lower hovering per unit mass. We propose that dietary sugar is a premium fuel for flight in nectarivorous, flying animals.

Cloning and functional expression of Rh50-like glycoprotein, a putative ammonia channel, in Aedes albopictus mosquitoes

Evidence has shown that female mosquitoes can deaminate more than 80% of the ingested bloodmeal protein amino acids, and thus lead to a massive amount of ammonia production. Ammonia transport is a critical step for detoxifying ammonia in organisms. Here we characterized a putative ammonia channel gene, Rhesus (Rh) 50 glycoprotein, from Aedes albopictus (AalRh50) and determined the difference of its expression profile in different tissues at both message and protein levels as well as its response to a blood meal. We showed that AalRh50 shares a low identity with E. coli ammonia transporter (EcoAmtB), but higher identities with human RhBG and Drosophila Rh50 genes. The analysis of ammonia-conductance sites indicates that AalRh50 has residue substitutions of S237L (equivalent to S219 in AmtB) in the external vestibule, F127I (equivalent to F107 in AmtB) in the pore entrance, and S281N (equivalent to S263 in AmtB) in the internal vestibule, which could alter or reduce ammonia-conductance activity. The results from quantitative real-time-PCR and immunohistochemistry revealed that AalRh50 is expressed at significantly higher levels in the head, Malpighian tubules, and thorax of the non-blood-fed females, suggesting that AalRh50 might play roles in maintaining normal neurotransmitter metabolism, acid-base balance, and flight energy production in different tissues of mosquitoes at the non-blood-fed condition. A blood meal significantly increases AalRh50 expression in midgut, fat body, and Malpighian tubules from 3 or 6 to 24h post feeding, indicating that AalRh50 plays an important role in detoxification of excess systemic ammonia of female adults during the gonotrophic cycle.

The adipokinetic hormone system in Culicinae (Diptera: Culicidae): molecular identification and characterization of two adipokinetic hormone (AKH) precursors from Aedes aegypti and Culex pipiens and two putative AKH receptor variants from A. aegypti

Insect neuropeptides of the adipokinetic hormone (AKH) family induce the mobilization of energy stores to fuel flight, but also affect the nutritional balance during diapause and oogenesis. They are therefore important regulators for flight, hibernation, and reproduction in mosquitoes including those that transmit human pathogens. In this study, we identified and analyzed the genes encoding two AKH preprohormones in the Yellow fever mosquito, Aedes aegypti: Aedae-AKH-I encodes the octapeptide pELFTPSWa and Aedae-AKH-II the decapeptide pEVTFSRDWNAa. Identical AKHs were identified in the West Nile virus vector, Culex pipiens, whose genes were characterized in this study as Culpi-AKH-I and Culpi-AKH-II. Using Northern blot, transcript expression was shown in A. aegypti, for Aedae-AKH-I in the head/thorax tissues of pupae and females, as well as in the abdomen of adult males; Aedae-AKH-II was only expressed in adults. In an immunocytological study using an AKH-antibody, the corpus cardiacum (CC), the intrinsic CC-cells (X-cells), the nervi corporis cardiaci, cells in the brain and thoracic ganglia were stained. In addition, two splice variants of the AKH-receptor gene were characterized in A. aegypti, (Aedae-AKHR-I and -II). RT-PCR revealed that both variants of these typical G-protein-coupled receptors were expressed in all life stages. Aedae-AKHR-I expression was also detected in the ovaries, indicating once more the influence of the AKH/AKHR system during the insect's oogenesis. Based on phylogenetic data, we postulate two closely related types of AKH-receptors that could bind selectively the two AKH peptides found in A. aegypti.

Stoichiometric estimates of the biochemical conversion efficiencies in tsetse metabolism

BACKGROUND

The time varying flows of biomass and energy in tsetse (Glossina) can be examined through the construction of a dynamic mass-energy budget specific to these flies but such a budget depends on efficiencies of metabolic conversion which are unknown. These efficiencies of conversion determine the overall yields when food or storage tissue is converted into body tissue or into metabolic energy. A biochemical approach to the estimation of these efficiencies uses stoichiometry and a simplified description of tsetse metabolism to derive estimates of the yields, for a given amount of each substrate, of conversion product, by-products, and exchanged gases. This biochemical approach improves on estimates obtained through calorimetry because the stoichiometric calculations explicitly include the inefficiencies and costs of the reactions of conversion. However, the biochemical approach still overestimates the actual conversion efficiency because the approach ignores all the biological inefficiencies and costs such as the inefficiencies of leaky membranes and the costs of molecular transport, enzyme production, and cell growth.

RESULTS

This paper presents estimates of the net amounts of ATP, fat, or protein obtained by tsetse from a starting milligram of blood, and provides estimates of the net amounts of ATP formed from the catabolism of a milligram of fat along two separate pathways, one used for resting metabolism and one for flight. These estimates are derived from stoichiometric calculations constructed based on a detailed quantification of the composition of food and body tissue and on a description of the major metabolic pathways in tsetse simplified to single reaction sequences between substrates and products. The estimates include the expected amounts of uric acid formed, oxygen required, and carbon dioxide released during each conversion. The calculated estimates of uric acid egestion and of oxygen use compare favorably to published experimental measurements.

CONCLUSION

This biochemical analysis provides reasonable first estimates of the conversion efficiencies for the major pathways used by tsetse metabolism. These results now enable a deeper analysis of tsetse ecology based on the construction of a dynamic mass-energy budget for tsetse and their populations.

Mitochondria: aerobic and anaerobic design--lessons from molluscs and fishes

The contributions of Peter Hochachka to the development of comparative and adaptational biochemistry are substantial. In particular, he and his academic offspring made major contributions to the understanding of the metabolism of molluscs and fishes. These two large taxonomic groups each have marine, freshwater and terrestrial/semiterrestrial representatives, and their mitochondrial metabolism has been shaped by these environmental conditions. In particular, the importance of amino acids and lipids as energy sources has interesting correlations with the environment and the osmotic strategy used. In marine molluscs, amino acids are important aerobic energy sources, and are used as osmolytes and participate in anaerobic metabolism. In marine elasmobranchs, amino acids and ketone bodies, but not lipids per se, are important energy sources in extrahepatic tissues. Marine and freshwater teleost fish by contrast use lipids as an extrahepatic energy source with minimal use of ketone bodies. Furthermore, ketone bodies are important in the metabolism of freshwater and terrestrial but not marine molluscs. The bases for these different metabolic plans may lie in the solute systems used by the different groups (e.g. amino acids in marine molluscs and urea in marine elasmobranchs). The various metabolic options used by fishes and molluscs indicate the plasticity of metabolic design in an environmental context.

Effects of proline analog binding on the spectroscopic and redox properties of PutA

The PutA flavoprotein regulates proline metabolism in Escherichia coli by performing two distinct functions. First, in the cytoplasm, PutA represses transcription of the put (proline utilization) regulon. Second, PutA associates with the membrane to oxidize proline to glutamate using discrete proline dehydrogenase and Delta(1)-pyrroline-5-carboxylate dehydrogenase domains. Here, we identify a proline analog that will be useful for testing the role substrate binding has in regulating PutA functions. L-Tetrahydro-2-furoic acid (L-THFA) was found to display simple competitive inhibition of proline dehydrogenase activity in PutA (apparent K(i)=0.2mM) and to perturb the flavin adenine dinucleotide (FAD) absorbance spectrum upon complexation to PutA. At pH 7.5, a reduction potential (E(m)) of -0.089V for the FAD/FADH(2) couple in L-THFA-complexed PutA was determined by potentiometric titrations. The E(m) value for L-THFA-complexed PutA is 12mV more negative than the E(m) for uncomplexed PutA (E(m)=-0.077V, pH 7.5) and corresponds to just a twofold increase in the dissociation constant of L-THFA with PutA upon reduction of FAD.

Cold tolerance and proline metabolic gene expression in Drosophila melanogaster

Treatment of Drosophila melanogaster adults with an inhibitor of protein synthesis led to a decrease in intrinsic cold-shock tolerance, but no difference in the rapid cold hardening response, which is apparent only if a period at 4 degrees C precedes the cold stress. Increases in energy reserves, including proline, were found in lines of flies selected for resistance to chilling injury. Since an increase in proline levels has been associated with overwintering in insects, and for salt and cold tolerance in plants, an RNase protection assay was developed to assess changes in transcript abundance for two genes encoding enzymes important for proline metabolism, pyrroline 5-carboxylate reductase and proline oxidase. The mRNA levels did not change in response to low temperature, but the high level of pyrroline 5-carboxylate reductase transcript is consistent with the interpretation that a large proline pool is important for Drosophila metabolism and survival during cold stress.

Insect acetyl-CoA carboxylase: enzyme activity during adult development and after feeding in the tsetse fly, Glossina morsitans

Acetyl-CoA carboxylase (EC 6.1.4.2) activity in the adult tsetse fly (Glossina morsitans) increased 2-3 days after pupation to reach a plateau of between 0.4 and 0.6 mumol/min/mg after 7 days, and between 0.6 and 0.8 mumol/min/mg after 6 days in the abdomens of male and female flies, respectively. The enzyme showed a 50-70% increase in specific activity within 20 hr after a blood meal in previously starved flies. Lipogenesis and acetyl-CoA carboxylase activity were detected in the thorax, the abdominal cuticle and, in greatest quantity, in the fat body.

Mechanism-based inhibition of proline dehydrogenase by proline analogues

The inactivation of proline dehydrogenase by several L-Pro analogues was investigated with the aim to block the essential metabolic pathway of tsetse flies allowing the degradation of L-Pro to L-Glu. In vitro studies on rat liver mitochondria showed that only 4-methylene-L-proline was able to inactivate proline dehydrogenase. The inactivation kinetics agreed with a mechanism-based inhibition. The other tested analogues E- and Z-4-fluoromethylene-L-proline, and cis and trans-5-ethynyl-D,L-proline were neither substrate nor inactivator of the enzyme. In vivo 4-methylene-L-proline showed no toxicity against Drosophila flies, but was lethal for Glossina pallidipes flies. This result allows the consideration of 4-methylene-L-proline as an attractive compound molecule in the struggle against tsetse flies.

Proline transport by tsetse fly Glossina morsitans flight muscle mitochondria

1. Proline accumulation by tsetse fly Glossina morsitans flight muscle mitochondria was studied in vitro by the swelling technique and direct measurement of (U-14C) proline. 2. Proline transport was inhibited by the uncharged liposoluble -SH reagent, N-ethylmaleimide but not by ionic reagent, mersalyl, suggesting that the -SH groups involved in the transport of proline are located in a hydrophobic part of the membrane or on the matrix side of the membrane. 3. The kinetic study of proline accumulation revealed saturation kinetics and a high temperature dependence. It gave a Km of 85 microM and a Vmax of 962 pmol/min/mg protein and an activation energy (Ea) of 11 kcal/mol. 4. Certain other amino acids (L-valine, L-alanine, L-methionine, L-phenylalanine, L-tryptophan and L-hydroxyproline) significantly stimulated proline uptake. 5. These observations indicate that tsetse fly Glossina morsitans flight muscle mitochondria contain a proline transport mechanism.

Glutamine and glutamate metabolism in normal and heat shock conditions inDrosophila Kc cells: Conditions supporting glutamine synthesis maximize heat shock polypeptide expression

We have previously reported that Drosophila Kc cells require glutamine for maximal expression of heat shock proteins in stressed conditions (Sanders and Kon: J. Cell. Physiol. 146:180-190, 1991). The mechanism of this effect has been investigated by comparing the metabolic utilization of glutamine in conditions which support hsp expression with that of glutamate in conditions where up to 100-fold less hsp is synthesized. This comparison showed that free ammonia was generated by cells incubated in the presence of glutamine in 37 degrees C (heat shock) conditions, but not at 25 degrees C, and not in the presence of glutamate in either normal or heat shock conditions. There was no difference in the amount of [14C]O2 generated from either [14C]-labeled amino acid in the tricarboxylic acid cycle, but three- to four-fold more alanine was synthesized in cells incubated in glutamine than in glutamate. Treating the cells with aminotransferase inhibitors to artificially increase NH3 release raised hsp expression in the presence of glutamate to maximal levels characteristic of glutamine. This potentiation correlated with inhibition of alanine aminotransferase. Since only NH3 production correlated with hsp expression in heat shock conditions in the presence of glutamine, and NH3 addition to glutamate also resulted in maximal hsp expression, we measured glutamine production in glutamate plus NH3 and observed net glutamine synthesis. The supposition that glutamine itself is responsible for the regulatory changes supporting maximal hsp expression was supported by the finding that the glutamine analog, 6-diazo-5-oxo-L-norleucine (DON), mimicked the effects of glutamine. We conclude that glutamine imposes regulatory changes which alter nitrogen metabolism and support hsp expression in Kc cells.

The isolation of mitochondria from dipteran flight muscle

Procedures for the isolation of mitochondria from dipteran flight muscle have been investigated in an attempt to determine the extent and to identify the causes of deterioration associated with isolation. In the light of the results obtained isolation procedures have been improved by minimising mechanical damage, avoiding the development of anoxic conditions, and by the use of an isolation medium of a more physiological nature, containing the potassium salt of an organic anion as the principal osmoeffector, phosphate as the principal buffer, and low concentrations of free Mg2+. The oxidative capacity of mitochondria isolated by the improved method is adequate to support the in vivo requirements of the flight system.