A novel 14-kDa V-ATPase subunit in the tobacco hornworm midgut

A quantitative micro-tomographic gut atlas of the lepidopteran model insect Manduca sexta

The tobacco hornworm is used extensively as a model system for ecotoxicology, immunology and gut physiology. Here, we established a micro-computed tomography approach based on the oral application of the clinical contrast agent iodixanol, allowing for a high-resolution quantitative analysis of the Manduca sexta gut. This technique permitted the identification of previously unknown and understudied structures, such as the crop or gastric ceca, and revealed the underlying complexity of the hindgut folding pattern, which is involved in fecal pellet formation. The acquired data enabled the volume rendering of all gut parts, the reliable calculation of their volumes, and the virtual endoscopy of the entire alimentary tract. It can provide information for accurate orientation in histology uses, enable quantitative anatomical phenotyping in three dimensions, and allow the calculation of locally effective midgut concentrations of applied chemicals. This atlas will provide critical insights into the evolution of the alimentary tract in lepidopterans.

Transcriptomic response of Anopheles gambiae sensu stricto mosquito larvae to Curry tree (Murraya koenigii) phytochemicals

BACKGROUND

Insect growth regulators (IGRs) can control insect vector populations by disrupting growth and development in juvenile stages of the vectors. We previously identified and described the curry tree (Murraya koenigii (L.) Spreng) phytochemical leaf extract composition (neplanocin A, 3-(1-naphthyl)-L-alanine, lumiflavine, terezine C, agelaspongin and murrayazolinol), which disrupted growth and development in Anopheles gambiae sensu stricto mosquito larvae by inducing morphogenetic abnormalities, reducing locomotion and delaying pupation in the mosquito. Here, we attempted to establish the transcriptional process in the larvae that underpins these phenotypes in the mosquito.

METHODS

We first exposed third-fourth instar larvae of the mosquito to the leaf extract and consequently the inherent phytochemicals (and corresponding non-exposed controls) in two independent biological replicates. We collected the larvae for our experiments sampled 24 h before peak pupation, which was 7 and 18 days post-exposure for controls and exposed larvae, respectively. The differences in duration to peak pupation were due to extract-induced growth delay in the larvae. The two study groups (exposed vs control) were consequently not age-matched. We then sequentially (i) isolated RNA (whole larvae) from each replicate treatment, (ii) sequenced the RNA on Illumina HiSeq platform, (iii) performed differential bioinformatics analyses between libraries (exposed vs control) and (iv) independently validated the transcriptome expression profiles through RT-qPCR.

RESULTS

Our analyses revealed significant induction of transcripts predominantly associated with hard cuticular proteins, juvenile hormone esterases, immunity and detoxification in the larvae samples exposed to the extract relative to the non-exposed control samples. Our analysis also revealed alteration of pathways functionally associated with putrescine metabolism and structural constituents of the cuticle in the extract-exposed larvae relative to the non-exposed control, putatively linked to the exoskeleton and immune response in the larvae. The extract-exposed larvae also appeared to have suppressed pathways functionally associated with molting, cell division and growth in the larvae. However, given the age mismatch between the extract-exposed and non-exposed larvae, we can attribute the modulation of innate immune, detoxification, cuticular and associated transcripts and pathways we observed to effects of age differences among the larvae samples (exposed vs control) and to exposures of the larvae to the extract.

CONCLUSIONS

The exposure treatment appears to disrupt cuticular development, immune response and oxidative stress pathways in Anopheles gambiae s.s larvae. These pathways can potentially be targeted in development of more efficacious curry tree phytochemical-based IGRs against An. gambiae s.s mosquito larvae.

Structural and Functional Characterization of Hermetia illucens Larval Midgut

The larvae of Hermetia illucens are among the most promising agents for the bioconversion of low-quality biomass, such as organic waste, into sustainable and nutritionally valuable proteins for the production of animal feed. Despite the great interest in this insect, the current literature provides information limited to the optimization of rearing methods for H. illucens larvae, with particular focus on their efficiency in transforming different types of waste and their nutritional composition in terms of suitability for feed production. Surprisingly, H. illucens biology has been neglected and a deep understanding of the morphofunctional properties of the larval midgut, the key organ that determines the extraordinary dietary plasticity of this insect, has been completely overlooked. The present study aims to fill this gap of knowledge. Our results demonstrate that the larval midgut is composed of distinct anatomical regions with different luminal pH and specific morphofunctional features. The midgut epithelium is formed by different cell types that are involved in nutrient digestion and absorption, acidification of the lumen of the middle region, endocrine regulation, and growth of the epithelium. A detailed characterization of the activity of enzymes involved in nutrient digestion and their mRNA expression levels reveals that protein, carbohydrate, and lipid digestion is associated to specific regions of this organ. Moreover, a significant lysozyme activity in the lumen of the anterior and middle regions of the midgut was detected. This enzyme, together with the strong acidic luminal pH of middle tract, may play an important role in killing pathogenic microorganisms ingested with the feeding substrate. The evidence collected led us to propose a detailed functional model of the larval midgut of H. illucens in which each region is characterized by peculiar features to accomplish specific functions. This platform of knowledge sets the stage for developing rearing protocols to optimize the bioconversion ability of this insect and its biotechnological applications.

Vacuolar H+-ATPase: An Essential Multitasking Enzyme in Physiology and Pathophysiology

Vacuolar H+-ATPases (V-ATPases) are large multisubunit proton pumps that are required for housekeeping acidification of membrane-bound compartments in eukaryotic cells. Mammalian V-ATPases are composed of 13 different subunits. Their housekeeping functions include acidifying endosomes, lysosomes, phagosomes, compartments for uncoupling receptors and ligands, autophagosomes, and elements of the Golgi apparatus. Specialized cells, including osteoclasts, intercalated cells in the kidney and pancreatic beta cells, contain both the housekeeping V-ATPases and an additional subset of V-ATPases, which plays a cell type specific role. The specialized V-ATPases are typically marked by the inclusion of cell type specific isoforms of one or more of the subunits. Three human diseases caused by mutations of isoforms of subunits have been identified. Cancer cells utilize V-ATPases in unusual ways; characterization of V-ATPases may lead to new therapeutic modalities for the treatment of cancer. Two accessory proteins to the V-ATPase have been identified that regulate the proton pump. One is the (pro)renin receptor and data is emerging that indicates that V-ATPase may be intimately linked to renin/angiotensin signaling both systemically and locally. In summary, V-ATPases play vital housekeeping roles in eukaryotic cells. Specialized versions of the pump are required by specific organ systems and are involved in diseases.

Ultrastructural and functional analysis of secretory goblet cells in the midgut of the lepidopteran Anticarsia gemmatalis

Defoliation caused by Anticarsia gemmatalis larvae affects the commercial production of the soybean. Although regulation of the digestion of soybean components has become part of the suggested strategy to overcome problems caused by Anticarsia larvae, few studies have focused on the morphological and cellular aspects of Anticarsia intestinal tissue. We have therefore further analyzed the morphology and ultrastructure of the midgut of 5th instar larvae of A. gemmatalis. Dissected midgut was subjected to chemical or cryo-fixation and then to several descriptive and analytical techniques associated with both light and electron microscopy in order to correlate anatomical and physiological aspects of this organ. Histological analysis revealed typical anatomy composed of a cell layer limited by a peritrophic membrane. The identified lepidoptera-specific goblet cells were shown to contain several mitochondria inside microvilli of the goblet cell cavity and a vacuolar H(+)-ATPase possibly coupled to a K(+)-pumping system. Columnar cells were present and exhibited microvilli dispersed along the apical region that also presented secretory characteristics. We additionally found evidence for the secretion of polyphosphate (PolyP) into the midgut, a result corroborating previous reports suggesting an excretion route from the goblet cell cavity toward the luminal space. Thus, our results suggest that the Anticarsia midgut not only possesses several typical lepidopteran features but also presents some unique aspects such as the presence of a tubular network and PolyP-containing apocrine secretions, plus an apparent route for the release of cellular debris by the goblet cells.

Solution structure of subunit F (Vma7p) of the eukaryotic V(1)V(O) ATPase from Saccharomyces cerevisiae derived from SAXS and NMR spectroscopy

Vacuolar ATPases use the energy derived from ATP hydrolysis, catalyzed in the A(3)B(3) sector of the V(1) ATPase to pump protons via the membrane-embedded V(O) sector. The energy coupling between the two sectors occurs via the so-called central stalk, to which subunit F does belong. Here we present the first low resolution structure of recombinant subunit F (Vma7p) of a eukaryotic V-ATPase from Saccharomyces cerevisiae, analyzed by small angle X-ray scattering (SAXS). The protein is divided into a 5.5nm long egg-like shaped region, connected via a 1.5nm linker to a hook-like segment at one end. Circular dichroism spectroscopy revealed that subunit F comprises of 43% α-helix, 32% β-sheet and a 25% random coil arrangement. To determine the localization of the N- and C-termini in the protein, the C-terminal truncated form of F, F(1-94) was produced and analyzed by SAXS. Comparison of the F(1-94) shape with the one of subunit F showed the missing hook-like region in F(1-94), supported by the decreased D(max) value of F(1-94) (7.0nm), and indicating that the hook-like region consists of the C-terminal residues. The NMR solution structure of the C-terminal peptide, F(90-116), was solved, displaying an α-helical region between residues 103 and 113. The F(90-116) solution structure fitted well in the hook-like region of subunit F. Finally, the arrangement of subunit F within the V(1) ATPase is discussed.

Vacuolar-type proton pumps in insect epithelia

Active transepithelial cation transport in insects was initially discovered in Malpighian tubules, and was subsequently also found in other epithelia such as salivary glands, labial glands, midgut and sensory sensilla. Today it appears to be established that the cation pump is a two-component system of a H(+)-transporting V-ATPase and a cation/nH(+) antiporter. After tracing the discovery of the V-ATPase as the energizer of K(+)/nH(+) antiport in the larval midgut of the tobacco hornworm Manduca sexta we show that research on the tobacco hornworm V-ATPase delivered important findings that emerged to be of general significance for our knowledge of V-ATPases, which are ubiquitous and highly conserved proton pumps. We then discuss the V-ATPase in Malpighian tubules of the fruitfly Drosophila melanogaster where the potential of post-genomic biology has been impressively illustrated. Finally we review an integrated physiological approach in Malpighian tubules of the yellow fever mosquito Aedes aegypti which shows that the V-ATPase delivers the energy for both transcellular and paracellular ion transport.

Cloning and expression analysis of midgut chymotrypsin-like proteinases in the tobacco hornworm

Digestion of proteins in the midgut of lepidopteran larvae relies on different trypsin and chymotrypsin isoforms. In this study we describe three chymotrypsin-like proteinases (CTLP2-4) from the larval midgut of Manduca sexta, which are closely related to CTLP1 and less closely related to another chymotrypsin (CT), two previously described proteinases present in the larval midgut of M. sexta. CTLP1-4 fit perfectly into a novel subgroup of insect CTLPs by sequence similarity and by the replacement of GP by SA in the highly conserved GDSGGP motif. When we examined CTLP expression in different tissues, most of the proteinases were predominantly expressed in the anterior and median midgut, while some were found in the Malpighian tubules. When we examined CTLP expression at different physiological states, we observed that the CTLP mRNA amounts did not differ considerably in feeding and starving larvae except for CTLP2, whose mRNA dropped significantly upon starvation. During moulting, however, the mRNA amounts of all CTLPs dropped significantly. When we immunologically examined CTLP amounts, mature proteinases were only detectable in the gut lumen of feeding and re-fed larvae, but not in that of starving or moulting larvae, suggesting that CTLP secretion is suspended during starvation or moult.

Characterization of vacuolar-ATPase and selective inhibition of vacuolar-H(+)-ATPase in osteoclasts

V-ATPase plays important roles in controlling the extra- and intra-cellular pH in eukaryotic cell, which is most crucial for cellular processes. V-ATPases are composed of a peripheral V(1) domain responsible for ATP hydrolysis and integral V(0) domain responsible for proton translocation. Osteoclasts are multinucleated cells responsible for bone resorption and relate to many common lytic bone disorders such as osteoporosis, bone aseptic loosening, and tumor-induced bone loss. This review summarizes the structure and function of V-ATPase and its subunit, the role of V-ATPase subunits in osteoclast function, V-ATPase inhibitors for osteoclast function, and highlights the importance of V-ATPase as a potential prime target for anti-resorptive agents.

The where, when, and how of organelle acidification by the yeast vacuolar H+-ATPase

All eukaryotic cells contain multiple acidic organelles, and V-ATPases are central players in organelle acidification. Not only is the structure of V-ATPases highly conserved among eukaryotes, but there are also many regulatory mechanisms that are similar between fungi and higher eukaryotes. These mechanisms allow cells both to regulate the pHs of different compartments and to respond to changing extracellular conditions. The Saccharomyces cerevisiae V-ATPase has emerged as an important model for V-ATPase structure and function in all eukaryotic cells. This review discusses current knowledge of the structure, function, and regulation of the V-ATPase in S. cerevisiae and also examines the relationship between biosynthesis and transport of V-ATPase and compartment-specific regulation of acidification.

Phylogeny and cloning of ion transporters in mosquitoes

Membrane transport in insect epithelia appears to be energized through proton-motive force generated by the vacuolar type proton ATPase (V-ATPase). However, secondary transport mechanisms that are coupled to V-ATPase activity have not been fully elucidated. Following a blood meal, the female mosquito regulates fluid and ion homeostasis through a series of characteristic behaviors that require brain-derived factors to regulate ion secretion. Despite the knowledge on the behaviors of the mosquito, little is known of the targets of several factors that have been implicated in cellular changes following a blood meal. This review discusses current models of membrane transport in insects and specific data on mosquito ion regulation together with the molecular aspects of membrane transport systems that are potentially linked to V-ATPase activity, which collectively determine the functioning of mosquito midgut and Malpighian tubules. Ion transport mechanisms will be discussed from a comparative physiology perspective to gain appreciation of the exquisite mechanisms of mosquito ion regulation.

Biochemical support for the V-ATPase rotary mechanism: antibody against HA-tagged Vma7p or Vma16p but not Vma10p inhibits activity

V-ATPase null mutants in yeast have a distinct, conditionally lethal phenotype that can be obtained through disruption of any one of its subunits. This enables supplementation of this mutant with the relevant subunit tagged with an epitope against which an antibody is available. In this system, the effect of antibody on the activity of the enzyme can be analyzed. Towards this end we used HA to tag subunits Vma7p, Vma10p and Vma16p, which are assumed to represent, respectively, the shaft, stator and turbine of the enzyme, and used them to supplement the corresponding yeast V-ATPase null mutants. The anti-HA epitope antibody inhibited both the ATP-dependent proton uptake and the ATPase activities of the Vma16p-HA and Vma7p-HA containing complexes, in intact vacuoles and in the detergent-solubilized enzyme. Neither of these activities was inhibited by the antibody in Vma10p-HA containing enzyme. These results support the function of Vma10p as part of the stator, while the other tagged subunits are part of the rotor apparatus. The HA-tag was attached to the N terminus of Vma16p; thus the antibody inhibition points to its accessibility outside the vacuolar membrane. This assumption is supported by the supplementation of the yeast mutant by the homologues of Vma16p isolated from Arabidopsis thaliana and lemon fruit c-DNA. Contrary to yeast, which has five predicted helices, the plant subunit Vma16p has only four. Our results confirm a recent report that only four of the yeast Vma16p complexes are actually transmembrane helices.

Concanamycin A, the specific inhibitor of V-ATPases, binds to the V(o) subunit c

Vacuolar-type ATPase (V-ATPase) purified from the midgut of the tobacco hornworm Manduca sexta is inhibited 50% by 10 nm of the plecomacrolide concanamycin A, the specific inhibitor of V-ATPases. To determine the binding site(s) of that antibiotic in the enzyme complex, labeling with the semisynthetic 9-O-[p-(trifluoroethyldiazirinyl)-benzoyl]-21,23-dideoxy-23-[(125)I]iodo-concanolide A (J-concanolide A) was performed, which still inhibits the V-ATPase 50% at a concentration of 15-20 microm. Upon treatment with UV light, a highly reactive carbene is generated from this concanamycin derivative, resulting in the formation of a covalent bond to the enzyme. In addition, the radioactive tracer (125)I makes the detection of the labeled subunit(s) feasible. Treatment of the V(1)/V(o) holoenzyme, the V(o) complex, and the V-ATPase containing goblet cell apical membranes with concanolide resulted in the labeling of only the proteolipid, subunit c, of the proton translocating V(o) complex. Binding of J-concanolide A to subunit c was prevented in a concentration-dependent manner by concanamycin A, indicating that labeling was specific. Binding was also prevented by the plecomacrolides bafilomycin A(1) and B(1), respectively, but not by the benzolactone enamide salicylihalamide, a member of a novel class of V-ATPase inhibitors.

Characterization of constitutive and putative differentially expressed mRNAs by means of expressed sequence tags, differential display reverse transcriptase-PCR and randomly amplified polymorphic DNA-PCR from the sand fly vector Lutzomyia longipalpis

Molecular studies of insect disease vectors are of paramount importance for understanding parasite-vector relationship. Advances in this area have led to important findings regarding changes in vectors' physiology upon blood feeding and parasite infection. Mechanisms for interfering with the vectorial capacity of insects responsible for the transmission of diseases such as malaria, Chagas disease and dengue fever are being devised with the ultimate goal of developing transgenic insects. A primary necessity for this goal is information on gene expression and control in the target insect. Our group is investigating molecular aspects of the interaction between Leishmania parasites and Lutzomyia sand flies. As an initial step in our studies we have used random sequencing of cDNA clones from two expression libraries made from head/thorax and abdomen of sugar fed L. longipalpis for the identification of expressed sequence tags (EST). We applied differential display reverse transcriptase-PCR and randomly amplified polymorphic DNA-PCR to characterize differentially expressed mRNA from sugar and blood fed insects, and, in one case, from a L. (V.) braziliensis-infected L. longipalpis. We identified 37 cDNAs that have shown homology to known sequences from GeneBank. Of these, 32 cDNAs code for constitutive proteins such as zinc finger protein, glutamine synthetase, G binding protein, ubiquitin conjugating enzyme. Three are putative differentially expressed cDNAs from blood fed and Leishmania-infected midgut, a chitinase, a V-ATPase and a MAP kinase. Finally, two sequences are homologous to Drosophila melanogaster gene products recently discovered through the Drosophila genome initiative.

Evidence for major structural changes in the Manduca sexta midgut V1 ATPase due to redox modulation. A small angle X-ray scattering study

The shape and overall dimensions of the oxidized and reduced form of the V(1) ATPase from Manduca sexta were investigated by synchrotron radiation x-ray solution scattering. The radius of gyration of the oxidized and reduced complex differ noticeably, with dimensions of 6. 20 +/- 0.06 and 5.84 +/- 0.06 nm, respectively, whereas the maximum dimensions remain constant at 22.0 +/- 0.1 nm. Comparison of the low resolution shapes of both forms, determined ab initio, indicates that the main structural alteration occurs in the head piece, where the major subunits A and B are located, and at the bottom of the stalk. In conjunction with the solution scattering data, decreased susceptibility to tryptic digestion and tryptophan fluorescence of the reduced V(1) molecule provide the first strong evidence for major structural changes in the V(1) ATPase because of redox modulation.

The multigene family of the tobacco hornworm V-ATPase: novel subunits a, C, D, H, and putative isoforms

The plasma membrane V-ATPase from Manduca sexta (Lepidoptera, Sphingidae) larval midgut is composed of at least 12 subunits, eight of which have already been identified molecularly [Wieczorek et al., J. Bioenerg. Biomembr. 31 (1999) 67-74]. Here we report primary sequences of subunits C, D, H and a, which previously had not been identified in insects. Expression of recombinant proteins, immunostaining and protein sequencing demonstrated that the corresponding proteins are subunits of the Manduca V-ATPase. Genomic Southern blot analysis indicated the existence of multiple genes encoding subunits G, a, c, d and e. Moreover, multiple transcripts were detected in Northern blots from midgut poly(A) RNA for subunits B, G, c and d. Thus, these polypeptides appear to exist as multiple isoforms that could be expressed either in different tissues or at distinct locations within a cell. By contrast subunits A, C, D, E, F and H appear to be encoded by single transcripts and therefore should be present in any Manduca V-ATPase, independent of its subcellular or cell specific origin.

Three-dimensional structure and subunit topology of the V(1) ATPase from Manduca sexta midgut

The three-dimensional structure of the Manduca sexta midgut V(1) ATPase has been determined at 3.2 nm resolution from electron micrographs of negatively stained specimens. The V(1) complex has a barrel-like structure 11 nm in height and 13.5 nm in diameter. It is hexagonal in the top view, whereas in the side view, the six large subunits A and B are interdigitated for most of their length (9 nm). The topology and importance of the individual subunits of the V(1) complex have been explored by protease digestion, resistance to chaotropic agents, MALDI-TOF mass spectrometry, and CuCl(2)-induced disulfide formation. Treatment of V(1) with trypsin or chaotropic iodide resulted in a rapid cleavage or release of subunit D from the enzyme, indicating that this subunit is exposed in the complex. Trypsin cleavage of V(1) decreased the ATPase activity with a time course that was in line with the cleavage of subunits B, C, G, and F. When CuCl(2) was added to V(1) in the presence of CaADP, the cross-linked products A-E-F and B-H were generated. In experiments where CuCl(2) was added after preincubation of CaATP, the cross-linked products E-F and E-G were formed. These changes in cross-linking of subunit E to near-neighbor subunits support the hypothesis that these are nucleotide-dependent conformational changes of the E subunit.

Trypanosoma cruzi: a putative vacuolar ATP synthase subunit and a CAAX prenyl protease-encoding gene, as examples of gene identification in genome projects

An international genome program has been initiated to increase the knowledge about the Trypanosoma cruzi genome and thereby find effective tools to treat Chagas' disease. We here report the molecular characterization of two novel genes found in the course of this project. Two of the open reading frames (ORF) identified in the sequencing of the third smallest chromosome of the CL Brener strain of T. cruzi were selected for further molecular characterization due to their similarity to genes with interesting functions in other organisms and their potential as targets to combat the parasite. The first ORF (402 bp) showed homology to a 14-kDa vacuolar ATP synthase subunit F from a variety of organisms, such as yeast, rat, bovine, human, and a number of prokaryotes. The second ORF (1188 bp) resembled a CAAX prenyl protease-encoding gene, identified in different organisms, including Homo sapiens, Saccharomyces cerevisiae, and Arabidopsis thaliana, as well as several prokaryotes. RT-PCR from T. cruzi total epimastigote RNA allowed us to isolate the complete transcripts of these genes. Furthermore, screening of an available normalized cDNA library derived from the same stage of the parasite confirmed that both genes are expressed at least in the epimastigote stage of T. cruzi. Comparison of the putative T. cruzi proteins to their counterparts in other organisms revealed significant protein sequence conservation over large evolutionary distances. Computer analysis revealed the presence of several motifs in both proteins, possibly related to the regulation and localization of these proteins in the parasite.

A novel insect V-ATPase subunit M9.7 is glycosylated extensively

Plasma membrane V-ATPase isolated from midgut and Malpighian tubules of the tobacco hornworm, Manduca sexta, contains a novel prominent 20-kDa polypeptide. Based on N-terminal protein sequencing, we cloned a corresponding cDNA. The deduced hydrophobic protein consisted of 88 amino acids with a molecular mass of only 9.7 kDa. Immunoblots of the recombinant 9.7-kDa polypeptide, using a monoclonal anti- body to the 20-kDa polypeptide, confirmed that the correct cDNA had been cloned. The 20-kDa polypeptide is glycosylated, as deduced from lectin staining. Treatment with N-glycosidase A resulted in the appearance of two additional protein bands of 16 and 10 kDa which both were immunoreactive to the 20-kDa polypeptide-specific monoclonal antibody. Thus, extensive N-glycosylation of the novel Vo subunit M9.7 accounts for half of its molecular mass observed in SDS-polyacrylamide gel electrophoresis. M9.7 exhibits some similarities to the yeast protein Vma21p which resides in the endoplasmic reticulum and is required for the assembly of the Vo complex. However, as deduced from immunoblots as well as from activities of the V-ATPase and endoplasmic reticulum marker enzymes in different membrane preparations, M9.7 is, in contrast to the yeast polypeptide, a constitutive subunit of the mature plasma membrane V-ATPase of M. sexta.

Vacuolar and plasma membrane proton-adenosinetriphosphatases

The vacuolar H+-ATPase (V-ATPase) is one of the most fundamental enzymes in nature. It functions in almost every eukaryotic cell and energizes a wide variety of organelles and membranes. V-ATPases have similar structure and mechanism of action with F-ATPase and several of their subunits evolved from common ancestors. In eukaryotic cells, F-ATPases are confined to the semi-autonomous organelles, chloroplasts, and mitochondria, which contain their own genes that encode some of the F-ATPase subunits. In contrast to F-ATPases, whose primary function in eukaryotic cells is to form ATP at the expense of the proton-motive force (pmf), V-ATPases function exclusively as ATP-dependent proton pumps. The pmf generated by V-ATPases in organelles and membranes of eukaryotic cells is utilized as a driving force for numerous secondary transport processes. The mechanistic and structural relations between the two enzymes prompted us to suggest similar functional units in V-ATPase as was proposed to F-ATPase and to assign some of the V-ATPase subunit to one of four parts of a mechanochemical machine: a catalytic unit, a shaft, a hook, and a proton turbine. It was the yeast genetics that allowed the identification of special properties of individual subunits and the discovery of factors that are involved in the enzyme biogenesis and assembly. The V-ATPases play a major role as energizers of animal plasma membranes, especially apical plasma membranes of epithelial cells. This role was first recognized in plasma membranes of lepidopteran midgut and vertebrate kidney. The list of animals with plasma membranes that are energized by V-ATPases now includes members of most, if not all, animal phyla. This includes the classical Na+ absorption by frog skin, male fertility through acidification of the sperm acrosome and the male reproductive tract, bone resorption by mammalian osteoclasts, and regulation of eye pressure. V-ATPase may function in Na+ uptake by trout gills and energizes water secretion by contractile vacuoles in Dictyostelium. V-ATPase was first detected in organelles connected with the vacuolar system. It is the main if not the only primary energy source for numerous transport systems in these organelles. The driving force for the accumulation of neurotransmitters into synaptic vesicles is pmf generated by V-ATPase. The acidification of lysosomes, which are required for the proper function of most of their enzymes, is provided by V-ATPase. The enzyme is also vital for the proper function of endosomes and the Golgi apparatus. In contrast to yeast vacuoles that maintain an internal pH of approximately 5.5, it is believed that the vacuoles of lemon fruit may have a pH as low as 2. Similarly, some brown and red alga maintain internal pH as low as 0.1 in their vacuoles. One of the outstanding questions in the field is how such a conserved enzyme as the V-ATPase can fulfill such diverse functions.

Cloning of soluble alkaline phosphatase cDNA and molecular basis of the polymorphic nature in alkaline phosphatase isozymes of Bombyx mori midgut

A cDNA coding for soluble type alkaline phosphatase (sALP) of Bombyx mori was isolated. Deduced amino acid sequence showed high identities to various ALPs and partial similarities to ATPase of Manduca sexta. Using this cDNA sequence as a probe, the molecular basis of electrophoretic polymorphism in sALP and membrane-bound type ALP (mALP) was studied. As for mALP, the result suggested that post-translational modification was important for the proteins to express activity and to represent their extensive polymorphic nature, whereas the magnitude of activities was mainly regulated by transcription. On the other hand, sALP zymogram showed poor polymorphism, but one exception was the null mutant, in which the sALP gene was largely lost. Interestingly, the sALP gene was shown to be transcribed into two mRNAs of different sizes, 2.0 and 2.4 Kb. In addition to the null mutant of sALP, we found a null mutant for mALP. Both of these mutants seem phenotypically silent, suggesting that the functional differentiation between these isozymes is not perfect, so that they can still work mutually and complement each other as an indispensable enzyme for B. mori.

Quaternary structure of V1 and F1 ATPase: significance of structural homologies and diversities

The V1 ATPase from the tobacco hornworm Manduca sexta and the Escherichia coli F1 ATPase were characterized by small-angle X-ray scattering (SAXS). The radii of gyration (Rg) of the complexes were 6.2 +/- 0.1 and 4.7 +/- 0.02 nm, respectively. The shape of the M. sexta V1 ATPase was determined ab initio from the scattering data showing six masses, presumed to be the A and B subunits, arranged in an alternating manner about a 3-fold axis. A seventh mass with a length of about 11.0 nm extends perpendicularly to the center of the hexameric unit. This central mass is presumed to be the stalk that connects V1 with the membrane domain (V(O)) in the intact V1V(O)-ATPase. In comparison, the shape of the F1 ATPase from E. coli possesses a quasi-3-fold symmetry over the major part of the enzyme. The overall asymmetry of the structure is given by a stem, assumed to include the central stalk subunits. The features of the V1 and F1 ATPase reveal structural homologies and diversities of the key components of the complexes.

Structure, function and regulation of the vacuolar (H+)-ATPases

The vacuolar (H+)-ATPases (or V-ATPases) function to acidify intracellular compartments in eukaryotic cells, playing an important role in such processes as receptor-mediated endocytosis, intracellular membrane traffic, protein degradation and coupled transport. V-ATPases in the plasma membrane of specialized cells also function in renal acidification, bone resorption and cytosolic pH maintenance. The V-ATPases are composed of two domains. The V1 domain is a 570-kDa peripheral complex composed of 8 subunits (subunits A-H) of molecular weight 70-13 kDa which is responsible for ATP hydrolysis. The V0 domain is a 260-kDa integral complex composed of 5 subunits (subunits a-d) which is responsible for proton translocation. The V-ATPases are structurally related to the F-ATPases which function in ATP synthesis. Biochemical and mutational studies have begun to reveal the function of individual subunits and residues in V-ATPase activity. A central question in this field is the mechanism of regulation of vacuolar acidification in vivo. Evidence has been obtained suggesting a number of possible mechanisms of regulating V-ATPase activity, including reversible dissociation of V1 and V0 domains, disulfide bond formation at the catalytic site and differential targeting of V-ATPases. Control of anion conductance may also function to regulate vacuolar pH. Because of the diversity of functions of V-ATPases, cells most likely employ multiple mechanisms for controlling their activity.

Cloning of the V-ATPase subunit G in plant: functional expression and sub-cellular localization

A 13-kDa tobacco plasma membrane protein was isolated from two-dimensional electrophoresis gels. After microsequencing, RT-PCR techniques and cDNA library screening allowed for the cloning of two cDNAs. These cDNAs encoded for the subunit G of the vacuolar H+-ATPase, the first one identified in plants. Analysis of mRNA distribution showed a maximum level in the leaves and in the stem of the apical part of the tobacco plant. Heterologous functional complementation of the yeast mutant (deltavma10::URA3) was achieved with the two cDNAs. After fractionation of microsomal membranes on linear sucrose gradient, Western blots were performed using antibodies against recombinant protein and three peaks were identified: one which comigrated with the tonoplast marker and the others at slightly higher density corresponding to endoplasmic reticulum and to plasma membrane fractions.

Release of two peripheral proteins from chloroplast thylakoid membranes in the presence of a Hofmeister series of chaotropic anions

The dissociation of two peripheral spinach (Spinacia oleracea L.) thylakoid membrane proteins, coupling factor CF1 and ferredoxin-NADP+-oxidoreductase, in the presence of chaotropic sodium salts has been investigated, using monospecific antibodies against the proteins as probes. Release of both proteins followed the Hofmeister series of anions (Cl- < NO3- < Br- < I- < SCN-). In mixtures, the different salts had an additive effect. In addition, there were also qualitative differences in the action of the anions, such that NaI and NaSCN led to a different concentration and time dependence of the dissociation of the peripheral proteins from thylakoids. An analysis of the temperature dependence of protein release showed that the more chaotropic ions reduced the activation energy required for the dissociation of the proteins from their binding sites on the membrane. The addition of sugars (glucose, sucrose, or trehalose) reduced the amount of protein released from the membranes in the presence of NaI or NaSCN.

Molecular characterization of the 50- and 57-kDa subunits of the bovine vacuolar proton pump

The vacuolar type proton-translocating ATPase of clathrin-coated vesicles is composed of two large domains: an extramembranous catalytic sector and a transmembranous proton channel. In addition, two polypeptides of 50 and 57 kDa have been found to co-purify with the pump. These proteins, termed SFD (sub-fifty-eight-kDa dimer) activate ATPase activity of the enzyme and couple ATPase activity to proton flow (Xie, X.-S., Crider, B.P., Ma, Y.-M., and Stone, D. K. (1994) J. Biol. Chem. 269, 28509-25815). It has also been reported that the clathrin-coated vesicle proton pump contains AP50, a 50-kDa component of the AP-2 complex responsible for the assembly of clathrin-coated pits, and that AP50 is essential for function of the proton pump (Liu, Q., Feng, Y., and Forgac, M. (1994) J. Biol. Chem. 269, 31592-31597). We demonstrate through the use of anti-AP50 antibody, identical to that of the latter study, that hydroxylapatite chromatography removes AP50 from impure proton pump preparations and that purified proton pump, devoid of AP50, is fully functional. To determine the true molecular identity of SFD, both the 50- and 57-kDa polypeptides were directly sequenced. A polymerase chain reaction-based strategy was used to screen a bovine brain cDNA library, yielding independent full-length clones (SFD-4A and SFD-21); these were identical in their open reading frames and encoded a protein with a predicted mass of 54,187 Da. The SFD-21 clone was then used in a reverse transcription-polymerase chain reaction-based strategy to isolate a related, but distinct, transcript present in bovine brain mRNA. The nucleotide and predicted amino acid sequences of this isolate are identical to SFD-21 except that the isolate contains a 54-base pair insert in the open reading frame, resulting in a protein with a predicted mass of 55,933 Da. Both clones had 16% identity to VMA13 of Saccharomyces cerevisiae. No sequence homology between the SFD clones and AP50 was detectable. Anti-peptide antibodies were generated against an epitope common to the two proteins and to the unique 18-amino acid insert of the larger protein. The former reacted with both components of native SFD, whereas the latter reacted only with the 57-kDa component. We term the 57- and 50-kDa polypeptides SFDalpha and SFDbeta, respectively.

Structure, function and regulation of the vacuolar (H+)-ATPase

The vacuolar (H+)-ATPases (or V-ATPases) function in the acidification of intracellular compartments in eukaryotic cells. The V-ATPases are multisubunit complexes composed of two functional domains. The peripheral V1 domain, a 500-kDa complex responsible for ATP hydrolysis, contains at least eight different subunits of molecular weight 70-13 (subunits A-H). The integral V0 domain, a 250-kDa complex, functions in proton translocation and contains at least five different subunits of molecular weight 100-17 (subunits a-d). Biochemical and genetic analysis has been used to identify subunits and residues involved in nucleotide binding and hydrolysis, proton translocation, and coupling of these activities. Several mechanisms have been implicated in the regulation of vacuolar acidification in vivo, including control of pump density, regulation of assembly of V1 and V0 domains, disulfide bond formation, activator or inhibitor proteins, and regulation of counterion conductance. Recent information concerning targeting and regulation of V-ATPases has also been obtained.

Sense and antisense RNA for the membrane associated 40 kDa subunit M40 of the insect V-ATPase

For the first time a cDNA encoding the membrane associated subunit M40 of an invertebrate V-ATPase has been isolated and sequenced, based on a cDNA library from larval midgut of the tobacco hornworm, Manduca sexta. Immunoblotting with monospecific antibodies raised against the recombinant M40 polypeptide demonstrated that it is a subunit of the insect plasma membrane V-ATPase. Since M40 subunits had been identified only in endosomal V-ATPases till now, this result indicates that they are constitutive members of all, endomembrane and plasma membrane V-ATPases. A phagemid clone representing a polyadenylated antisense transcript was also isolated and sequenced. Using RT-PCR, endogenous antisense RNA was detected in poly(A) RNA isolated from the larval midgut. Since Southern blots indicated a single gene locus, both the antisense RNA as well as the sense mRNA encoding subunit M40 seem to originate from the same gene.

Site-directed mutagenesis of the yeast V-ATPase A subunit

To investigate the function of residues at the catalytic nucleotide binding site of the V-ATPase, we have carried out site-directed mutagenesis of the VMA1 gene encoding the A subunit of the V-ATPase in yeast. Of the three cysteine residues that are conserved in all A subunits sequenced thus far, two (Cys284 and Cys539) appear essential for correct folding or stability of the A subunit. Mutation of the third cysteine (Cys261), located in the glycine-rich loop, to valine, generated an enzyme that was fully active but resistant to inhibition by N-ethylmalemide, 7-chloro-4-nitrobenz-2-oxa-1,3-diazole, and oxidation. To test the role of disulfide bond formation in regulation of vacuolar acidification in vivo, we have also determined the effect of the C261V mutant on targeting and processing of the soluble vacuolar protein carboxypeptidase Y. No difference in carboxypeptidase Y targeting or processing is observed between the wild type and C261V mutant, suggesting that disulfide bond formation in the V-ATPase A subunit is not essential for controlling vacuolar acidification in the Golgi. In addition, fluid phase endocytosis of Lucifer Yellow, quinacrine staining of acidic intracellular compartments and cell growth are indistinguishable in the C261V and wild type cells. Mutation of G250D in the glycine-rich loop also resulted in destabilization of the A subunit, whereas mutation of the lysine residue in this region (K263Q) gave a V-ATPase complex which showed normal levels of A subunit on the vacuolar membrane but was unstable to detergent solubilization and isolation and was totally lacking in V-ATPase activity. By contrast, mutation of the acidic residue, which has been postulated to play a direct catalytic role in the homologous F-ATPases (E286Q), had no effect on stability or assembly of the V-ATPase complex, but also led to complete loss of V-ATPase activity. The E286Q mutant showed labeling by 2-azido-[32P]ATP that was approximately 60% of that observed for wild type, suggesting that mutation of this glutamic acid residue affected primarily ATP hydrolysis rather than nucleotide binding.

Characterization and subunit structure of the ATP synthase of the halophilic archaeon Haloferax volcanii and organization of the ATP synthase genes

The archaeal ATPase of the halophile Haloferax volcanii synthesizes ATP at the expense of a proton gradient, as shown by sensitivity to the uncoupler carboxyl cyanide p-trifluoromethoxyphenylhydrazone, to the ionophore nigericin, and to the proton channel-modifying reagent N,N'-dicyclohexylcarbodiimide. The conditions for an optimally active ATP synthase have been determined. We were able to purify the enzyme complex and to identify the larger subunits with antisera raised against synthetic peptides. To identify additional subunits of this enzyme complex, we cloned and sequenced a gene cluster encoding five hydrophilic subunits of the A1 part of the proton-translocating archaeal ATP synthase. Initiation, termination, and ribosome-binding sequences as well as the result of a single transcript suggest that the ATPase genes are organized in an operon. The calculated molecular masses of the deduced gene products are 22. 0 kDa (subunit D), 38.7 kDa (subunit C), 11.6 kDa (subunit E), 52.0 kDa (subunit B), and 64.5 kDa (subunit A). The described operon contains genes in the order D, C, E, B, and A; it contains no gene for the hydrophobic, so-called proteolipid (subunit c, the proton-conducting subunit of the A0 part). This subunit has been isolated and purified; its molecular mass as deduced by SDS-polyacrylamide gel electrophoresis is 9.7 kDa.

Identification and characterization of differentially expressed cDNAs of the vector mosquito, Anopheles gambiae

The isolation and study of Anopheles gambiae genes that are differentially expressed in development, notably in tissues associated with the maturation and transmission of the malaria parasite, is important for the elucidation of basic molecular mechanisms underlying vector-parasite interactions. We have used the differential display technique to screen for mRNAs specifically expressed in adult males, females, and midgut tissues of blood-fed and unfed females. We also screened for mRNAs specifically induced upon bacterial infection of larval stage mosquitoes. We have characterized 19 distinct cDNAs, most of which show developmentally regulated expression specificity during the mosquito life cycle. The most interesting are six new sequences that are midgut-specific in the adult, three of which are also modulated by blood-feeding. The gut-specific sequences encode a maltase, a V-ATPase subunit, a GTP binding protein, two different lectins, and a nontrypsin serine protease. The latter sequence is also induced in larvae subjected to bacterial challenge. With the exception of a mitochondrial DNA fragment, the other 18 sequences constitute expressed genomic sequence tags, 4 of which have been mapped cytogenetically.

Purification and properties of a cytosolic V1-ATPase

The native V1 complex of the tobacco hornworm vacuolar type ATPase (V-ATPase) was purified from cytosolic extracts of molting larval midgut. It consisted of the established V-ATPase subunits A, B, and E along with the 14-kDa subunit F and the novel 13-kDa subunit G. The final amount of purified V1 complex made up an unexpectedly high 2% of the total cytosolic protein, with a yield of approximately 0.4 mg/g of tissue. An equally high amount of cytosolic V1 complex was obtained from starving intermolt larvae. By contrast, the cytosolic V1 pool was reduced drastically in feeding intermolt larvae or in larvae that had been refed after starvation. The activity of the membrane-bound V-ATPase holoenzyme was inversely related to the size of the cytosolic V1 pool, suggesting that the insect plasma membrane V-ATPase is regulated by reversible disassembly of the V1 complex as a function of the feeding condition of the larvae. Like F1-ATPases, the purified V1 complex exhibited Ca2+-dependent ATPase activity and, in the presence of 25% methanol, exhibited Mg2+-dependent ATPase activity. Therefore, we designate the native V1 complex, V1-ATPase. Both enzyme activities were completely inhibited by micromolar N-ethylmaleimide. In contrast to the Ca2+-dependent V1-ATPase activity, the Mg2+/methanol-dependent V1-ATPase activity did not decrease with the incubation time and thus was not inhibited by ADP. Methanol appears to induce a conformational change of the V1 complex, leading to enzymatic properties of the V1-ATPase that are similar to those of the membrane-bound V-ATPase holoenzyme. This is the first time that a native and enzymatically active V1 complex has been purified from the cytosol.

Characterisation of vha26, the Drosophila gene for a 26 kDa E-subunit of the vacuolar ATPase

A Drosophila melanogaster gene and cDNA for the E-subunit of the V-ATPase were characterised. The deduced product has 226 amino acids and a molecular mass of 26.1 kDa. The gene is a single copy at 83B1-4 on chromosome 3R. The coding sequence is punctuated by three introns which do not align with those in Neurospora. The gene is ubiquitously expressed as an mRNA of 2.3 kb. but at lower levels in pupae.

Subunit structure and organization of the genes of the A1A0 ATPase from the Archaeon Methanosarcina mazei Gö1

The proton-translocating A1A0 ATP synthase/hydrolase of Methanosarcina mazei Gö1 was purified and shown to consist of six subunits of molecular masses of 65, 49, 40, 36, 25, and 7 kDa. Electron microscopy revealed that this enzyme is organized in two domains, the hydrophilic A1 and the hydrophobic A0 domain, which are connected by a stalk. Genes coding for seven hydrophilic subunits were cloned and sequenced. From these data it is evident that the 65-, 49-, 40- and 25-kDa subunits are encoded by ahaA, ahaB, ahaC, and ahaD, respectively; they are part of the A1 domain or the stalk. In addition there are three more genes, ahaE, ahaF, and ahaG, encoding hydrophilic subunits, which were apparently lost during the purification of the protein. The A0 domain consists of at least the 7-kDa proteolipid and the 36-kDa subunit for which the genes have not yet been found. In summary, it is proposed that the A1A0 ATPase of Methanosarcina mazei Gö1 contains at least nine subunits, of which seven are located in A1 and/or the stalk and two in A0.

The Drosophila melanogaster gene vha14 encoding a 14-kDa F-subunit of the vacuolar ATPase

A Drosophila melanogaster (Dm) cDNA (vha14) encoding the 14-kDa F-subunit of the vacuolar H(+)-ATPase (V-ATPase) has been cloned via homology with the corresponding Manduca sexta (Ms) gene. Its deduced translation product is a 124-amino-acid polypeptide sharing 90% identity with the Ms polypeptide and 50% identity with an analogous polypeptide of Saccharomyces cerevisiae, and a more distant similarity to a subunit of the Na(+)-transporting ATPase of Enterococcus hirae. Homology was also found with expressed sequence tags from man, Arabidopsis thaliana, Caenorhabditis elegans and C. briggsiae, Oryza sativa and Plasmodium falciparum, indicating that the subunit is phylogenetically conserved. The Dm gene (vha14) is present as a single copy at cytological position 52B on the second chromosome, and gives rise to an mRNA species of 0.65 kb. Expression of the latter shows relatively little variation during development, or between adult head, thorax and abdomen, suggesting that the F-subunit is a relatively ubiquitous component of the V-ATPase.

The peripheral complex of the tobacco hornworm V-ATPase contains a novel 13-kDa subunit G

A prominent 16-kDa protein copurifies with the V-ATPase isolated from both posterior midgut and Malpighian tubules of Manduca sexta larvae and thus was believed to represent a V-ATPase subunit. [14C]N,N'-dicyclohexylcarbodiimide labeling and its position on SDS-electrophoresis gels revealed that this protein was different from the 17-kDa proteolipid. A cDNA clone encoding a highly hydrophilic protein with a calculated molecular mass of 13,692 Da was obtained by immunoscreening. Monospecific antibodies, affinity-purified to the 13-kDa recombinant protein expressed in Escherichia coli, specifically recognized the 16-kDa protein of the purified V-ATPase, confirming that a cDNA encoding this protein had been cloned. In vitro translation of the cRNA showed that the cloned 13-kDa subunit behaved like a 16-kDa protein on SDS-electrophoresis gels. The cloned protein showed 37% amino acid sequence identity to the 13-kDa V-ATPase subunit Vma10p recently cloned from yeast and some similarity to subunit b of bacterial F-ATPases. In contrast to the Vma10p protein, which behaved like a V0 subunit, the M. sexta 13-kDa protein behaved like a V1 subunit, since it could be stripped from the membrane by treatment with the chaotropic salt KI and by cold inactivation. When KI dissociated V-ATPase subunits were reassociated by dialysis that removed the KI, a soluble, 450-kDa complex of the M. sexta V-ATPase could be purified by gel chromatography. This V1 complex consisted of subunits A, B, E, and the 13-kDa subunit, confirming that the cloned protein is a new V-ATPase subunit and a member of the peripheral V1 complex of the V-ATPase. We designate this new V1 component subunit G.

Identification of a 14-kDa subunit associated with the catalytic sector of clathrin-coated vesicle H+-ATPase

The clathrin-coated vesicle H+-ATPase is composed of a peripheral catalytic sector (VC) and an integral membrane proton channel (VB), both of which are multiple subunit complexes. This study was conducted to determine if subunit F, previously identified in vacuolar proton pumps of tobacco hornworm and yeast, was present in mammalian pumps. Using a polymerase chain reaction-based strategy, we have isolated and sequenced cDNA clones from bovine and rat brain cDNA libraries. A full-length clone from rat brain encodes a 119-amino acid polypeptide with a predicted molecular mass of 13, 370 Da and with approximately 72 and 49% identity to subunit F of tobacco hornworm and yeast, respectively. Southern and Northern blot analyses indicate that the protein is encoded by a single gene. An anti-peptide antibody, directed against deduced protein sequence, was affinity-purified and shown to react with a 14-kDa polypeptide that is present in a highly purified pump prepared from clathrin-coated vesicles and also isolated VC. When stripped clathrin-coated vacuolars and purified chromaffin granule membranes were treated with KI in the presence of ATP, the 14-kDa subunit was released from both membranes, further indicating that it is part of the peripheral catalytic sector. In addition, direct sequencing of this 14-kDa component of the coated vacuolar proton pump confirmed its identity as a subunit F homologue.

The Saccharomyces cerevisiae VMA10 is an intron-containing gene encoding a novel 13-kDa subunit of vacuolar H(+)-ATPase

The vacuolar H(+)-ATPase (V-ATPase) functions as a primary proton pump that generates an electrochemical gradient of protons across the membranes of several internal organelles. It is composed of distinct catalytic and membrane sectors, each containing several subunits. We identified a protein (M16) that copurifies with the V-ATPase complex from Saccharomyces cerevisiae and appears to be present at multiple copies/enzyme. Amino acid sequencing of its proteolytic products yielded three nonoverlapping peptide sequences matching an unidentified reading frame located on chromosome VIII. Sequence analysis of cDNA encoding M16 revealed that the gene encoding this protein (VMA10) is interrupted by a 162-nucleotide intron that begins after the ATG codon of the initiator methionine. The cDNA encodes an hydrophilic protein of 12,713 Da with a basic isoelectric point of pH 9. A delta vma10::URA3 null mutant exhibited growth characteristics typical of other vma disruptant mutants in genes encoding subunits of V-ATPase. The null mutant does not grow on medium buffered at pH 7.5. It fails to accumulate quinacrine into its vacuole, and subunits of the catalytic sector are not assembled onto the vacuolar membrane in the absence of M16. A cold inactivation experiment demonstrated that M16 is a subunit of the membrane sector of V-ATPase. M16 exhibits a significant sequence homology with subunit b of F-ATPase membrane sector.

Regulation of plasma membrane V-ATPase activity by dissociation of peripheral subunits

The plasma membrane V-ATPase of Manduca sexta larval midgut is an electrogenic proton pump located in goblet cell apical membranes (GCAM); it energizes, by the voltage component of its proton motive force, an electrophoretic K+/nH+ antiport and thus K+ secretion (Wieczorek, H., Putzenlechner, M., Zeiske, W., and Klein, U. (1991) J. Biol Chem. 266, 15340-15347). Midgut transepithelial voltage, indicating net active K+ transport, was found to be more than 100 mV during intermoult stages but was abolished during moulting. Simultaneously, ATP hydrolysis and ATP-dependent proton transport in GCAM vesicles were found to be reduced to 10-15% of the intermoult level. Immunocytochemistry of midgut cryosections as well as SDS-polyacrylamide gel electrophoresis and immunoblots of GCAM demonstrated that loss of ATPase activity paralleled the disappearance of specific subunits. The subunits missing were those considered to compose the peripheral V1 sector, whereas the membrane integral V0 subunits remained in the GCAM of moulting larvae. The results provide, for the first time, evidence that a V-ATPase activity can be controlled in vivo by the loss of the peripheral V1 domain.

Phenylglyoxal suppresses cationic lysine/K+ symport under alkaline conditions in brush border membrane vesicles from larval Manduca sexta midgut

The arginine-specific reagent, phenylglyoxal, decreases the initial rate of lysine/K+ symport (cotransport) as well as maximum lysine accumulation at pH 9.2, by brush border membrane vesicles obtained from the larval midgut of the lepidopteran, Manduca sexta. The symport of a neutral amino acid, leucine, remained unaffected. Following exposure to phenylglyoxal, the apparent dissociation constant for lysine increased by a factor of 2.5 whereas the maximum uptake rate decreased by a factor of 0.4. More than one arginine residue appears to react with phenylglyoxal. Apparently phenylglyoxal reacts preferentially with arginine residues on a symporter that is specific for positively charged lysine. Phenylglyoxal shows promise as a specific covalent label for the identification of a cationic amino acid symporter.