Stable association of chloroplastic precursors with protein translocation complexes that contain proteins from both envelope membranes and a stromal Hsp100 molecular chaperone

Cytoplasmically synthesized precursors interact with translocation components in both the outer and inner envelope membranes during transport into chloroplasts. Using co-immunoprecipitation techniques, with antibodies specific to known translocation components, we identified stable interactions between precursor proteins and their associated membrane translocation components in detergent-solubilized chloroplastic membrane fractions. Antibodies specific to the outer envelope translocation components OEP75 and OEP34, the inner envelope translocation component IEP110 and the stromal Hsp100, ClpC, specifically co-immunoprecipitated precursor proteins under limiting ATP conditions, a stage we have called docking. A portion of these same translocation components was co-immunoprecipitated as a complex, and could also be detected by co-sedimentation through a sucrose density gradient. ClpC was observed only in complexes with those precursors utilizing the general import apparatus, and its interaction with precursor-containing translocation complexes was destabilized by ATP. Finally, ClpC was co-immunoprecipitated with a portion of the translocation components of both outer and inner envelope membranes, even in the absence of added precursors. We discuss possible roles for stromal Hsp100 in protein import and mechanisms of precursor binding in chloroplasts.

Identification of protein transport complexes in the chloroplastic envelope membranes via chemical cross-linking

Transport of cytoplasmically synthesized proteins into chloroplasts uses an import machinery present in the envelope membranes. To identify the components of this machinery and to begin to examine how these components interact during transport, chemical cross-linking was performed on intact chloroplasts containing precursor proteins trapped at a particular stage of transport by ATP limitation. Large cross-linked complexes were observed using three different reversible homobifunctional cross-linkers. Three outer envelope membrane proteins (OEP86, OEP75, and OEP34) and one inner envelope membrane protein (IEP110), previously reported to be involved in protein import, were identified as components of these complexes. In addition to these membrane proteins, a stromal member of the hsp100 family, ClpC, was also present in the complexes. We propose that ClpC functions as a molecular chaperone, cooperating with other components to accomplish the transport of precursor proteins into chloroplasts. We also propose that each envelope membrane contains distinct translocation complexes and that a portion of these interact to form contact sites even in the absence of precursor proteins.

Structural characterization and intramolecular aliphatic C-H oxidation ability of M(III)(mu-O)2M(III) complexes of Ni and Co with the hydrotris-(3,5-dialkyl-4-X-pyrazolyl)borate ligands TpMe2,X (X = Me, H, Br) and TpiPr2

Reaction of the dinuclear M(II)-bis(mu-hydroxo) complexes of nickel and cobalt, [(M(II)(TpR)]2(mu-OH)2] (M = Ni; 3Ni M = Co: 3Co), with one equivalent of H2O2 yields the corresponding M(III)-bis(mu-oxo) complexes, [[M(III)(TpR)]2-(mu-O)2] (M=Ni; 2Ni, M=Co: 2Co). The employment of a series of TpMe2,X (TpMe2,X = hydrotris(3,5-dimethyl-4-X-1-pyrazolyl)borate; X = Me, H, Br) as a metal supporting ligand makes it possible to isolate and structurally characterize the thermally unstable M(III)-bis-(mu-oxo) complexes 2Ni and 2Co. Both the starting (3Ni and 3Co) and resulting complexes (2Ni and 2Co) contain five-coordinate metal centers with a slightly distorted square-pyramidal geometry. Characteristic features of the nickel complexes 2Ni, such as the two intense absorptions around 400 and 300 nm in the UV-visible spectra and the apparent diamagnetism, are very similar to those of the previously reported bis(mu-oxo) species of Cu(III) and Ni(III) with ligands other than TpR, whereas the spectroscopic properties of the cobalt complexes 2Co (i.e., paramagnetically shifted NMR signals and a single intense absorption appearing at 350 nm) are clearly distinct from those of the isostructural nickel compounds 2Ni. Thermal decomposition of 2Ni and 2Co results in oxidation of the inner saturated hydrocarbyl substituents of the TpR ligand. Large kH/kD values obtained from the first-order decomposition rates of the TpMe3 and Tp(CD3)2,Me derivatives of 2 evidently indicate that the rate-determining step is an hydrogen abstraction from the primary C-H bond of the methyl substituents. mediated by the M(III)2-(mu-O)2 species. The nickel complex 2Ni shows reactivity about 10(3) times greater than that of the cobalt analogue 2Co. The oxidation ability of the M(III)(mu-O)2M(III) core should be affected by the hindered TpR ligand system, which can stabilize the +2 oxidation state of the metal centers.

SecA, an essential component of the secretory machinery of Escherichia coli, exists as homodimer

Size exclusion chromatography of the cytosolic fraction of SecA-overproducing cells of Escherichia coli suggested that SecA, an essential component of the secretory machinery, exists as an oligomer. The subunit structure of SecA was then studied using a purified specimen. Estimation of the molecular mass by means of ultracentrifugation and chemical crosslinking analysis revealed that SecA exists as a homodimer. The purified SecA was denatured in 6 M guanidine-HCl and renatured to a dimer, which was fully active in terms of translocation, even in the presence of 1 mM dithiothreitol. It is suggested that the dimeric structure is not critically maintained by disulfide bonding between the two subunits, each of which contains four cysteine residues.

Enzymatic properties and nucleotide and amino acid sequences of a thermostable beta-agarase from a novel species of deep-sea Microbulbifer

An agar-degrading bacterium, strain JAMB-A7, was isolated from the sediment in Sagami Bay, Japan, at a depth of 1,174 m and identified as a novel species of the genus Microbulbifer. The gene for a novel beta-agarase from the isolate was cloned and sequenced. It encodes a protein of 441 amino acids with a calculated molecular mass of 48,989 Da. The deduced amino acid sequence showed similarity to those of known beta-agarases in glycoside hydrolase family 16, with only 34-55% identity. A sequence similar to a carbohydrate-binding module was found in the C-terminal region of the enzyme. The recombinant agarase was hyper-produced extracellularly using Bacillus subtilis as the host, and the enzyme purified to homogeneity had a specific activity of 398 U (mg protein)(-1) at pH 7.0 and 50 degrees C. It was thermostable, with a half-life of 502 min at 50 degrees C. The optimal pH and temperature for activity were around 7 and 50 degrees C, respectively. The pattern of agarose hydrolysis showed that the enzyme was an endo-type beta-agarase, and the final main product was neoagarotetraose. The activity was not inhibited by NaCl, EDTA, and various surfactants at high concentrations. In particular, sodium dodecyl sulfate had no inhibitory effect up to 2%.

Molecular chaperones involved in chloroplast protein import

Transport of cytoplasmically synthesized precursor proteins into chloroplasts, like the protein transport systems of mitochondria and the endoplasmic reticulum, appears to require the action of molecular chaperones. These molecules are likely to be the sites of the ATP hydrolysis required for precursor proteins to bind to and be translocated across the two membranes of the chloroplast envelope. Over the past decade, several different chaperones have been identified, based mainly on their association with precursor proteins and/or components of the chloroplast import complex, as putative factors mediating chloroplast protein import. These factors include cytoplasmic, chloroplast envelope-associated and stromal members of the Hsp70 family of chaperones, as well as stromal Hsp100 and Hsp60 chaperones and a cytoplasmic 14-3-3 protein. While many of the findings regarding the action of chaperones during chloroplast protein import parallel those seen for mitochondrial and endoplasmic reticulum protein transport, the chloroplast import system also has unique aspects, including its hypothesized use of an Hsp100 chaperone to drive translocation into the organelle interior. Many questions concerning the specific functions of chaperones during protein import into chloroplasts still remain that future studies, both biochemical and genetic, will need to address.

SecA protein is directly involved in protein secretion in Escherichia coli

A high-expression plasmid for the secA gene was constructed. The SecA protein was then overproduced in E. coli and purified. The purified SecA stimulated the in vitro translocation of a model secretory protein into inverted membrane vesicles pretreated with 4 M urea. Membrane vesicles from a secAts mutant exhibited lower translocation activity, which was enhanced by SecA. These results indicate that SecA is directly involved in protein secretion across the cytoplasmic membrane.

Age-related development of the arrangement of connective tissue fibers in the lamina propria of the human vocal fold

A scanning electron microscopic study was made on the morphological changes occurring with age in collagen and elastic fibers in the lamina propria of the human vocal fold. We obtained the specimens from 32 autopsy cases ranging from 20 gestational weeks to 22 postnatal years and submitted them to digestion treatments with 10% sodium hydroxide and 90% formic acid. The vocal folds in fetuses and neonates consisted of sparse and dense areas of collagen and elastic fibers, and the vocal ligament was not found. In subjects 5 years of age, a deep dense area was found in the anterior and posterior maculae flavae, and longitudinal fibers were noted between the maculae. A structure of superficial versus deep layers appeared in children older than 10 years of age. The layered structure of the lamina propria was complete around 17 years of age. The development of the layered structure and the maturity of the fibers appeared to reflect the complexity of phonatory function during adolescence.

Ultrastructure of the lamina propria of the human vocal fold

We studied three-dimensional arrangement of collagen fibers and elastic fibers in the human vocal fold by scanning electron microscopy after digesting cellular elements and collagen fibers with formic acid treatment and cellular elements and elastic fibers with 10% sodium hydroxide. The superficial layer consisted of clusters of collagen fibers and fine elastic fibers running straight or coiled. The intermediate layer consisted of thick bundles of collagen and elastic fibers running longitudinally and fine coiled elastic fibers. The deep layer consisted of coil elastic fibers and dense collagen bundles. Collagen fibers may have a role of maintaining the organization of vocal folds even during vibration, and elastic fibers act to rapidly restore the vocal folds to their original form. We also studied the distribution of oxytalan fibers in vocal folds by aldehyde-fucusin staining. Oxytalan fibers were distributed throughout the connective tissue of the vocal folds, and a large number of fibers was present just under the epithelial basement membrane and around the muscle fibers. If these fibers are damaged and lose their functions, vibration of the vocal folds will be impaired.

Unilateral anomalous left common carotid artery; a case report

An anomaly of the left common carotid artery was observed in a Japanese male cadaver during an anatomy class at the Saitama Medical School in 1995. The superior thyroid, lingual and facial arteries arose from the common carotid artery, and the posterior auricular, maxillary and superficial temporal arteries arose from the common carotid artery by a common trunk. The occipital and ascending pharyngeal arteries arose from the internal carotid artery. The left carotid body (glomus caroticum) was observed to be slightly below the lingual artery, behind the common carotid artery, and it was located at the level of the intervertebral disk between C2 and C3 or at the same level as the right carotid body. The carotid body was richly innervated by a branch of the glossopharyngeal nerve and by a plexus of sympathetic fibers from the vagus and glossopharyngeal nerves. We assumed that the artery above the level of the carotid body was the internal carotid artery; there was no specific external carotid artery and all branches of the external carotid artery arose from the internal carotid artery.

The first structure of pectate lyase belonging to polysaccharide lyase family 3

The crystal structure of a highly alkaline low molecular weight pectate lyase (Pel-15) was determined at 1.5 A resolution by the multiple isomorphous replacement (MIR) method. This is the first pectate lyase structure from polysaccharide lyase family 3. The overall structure is a simple eight-turn right-handed parallel beta-helix domain with one long loop protruding from one side of the beta-helix. The low molecular weight of Pel-15 derives from the lack of N- and C-terminal extensions that are found in many beta-helix proteins. Although the structure has one calcium ion at pH 6.7, raising the pH to 9.5 results in the binding of an additional calcium ion. The common calcium ion found in both the pH 6.5 and 9.5 structures seems to stabilize both the beta-helix structure and the long protruding loop. The additional calcium ion found in the pH 9.5 structure alone may neutralize the acidic substrate. The region around the additional calcium ion is thought to bind to the substrate, as this region is rich in charged amino-acid residues which are required in catalysis.

Purification and characterization of enterotoxin produced by Aeromonas sobria

We purified the toxin of Aeromonas sobria capable of inducing a positive response in the mouse intestinal loop assay. The purified toxin showed a positive response not only in the loop assay but also in a hemolytic assay. Subsequently, we cloned the toxin gene and demonstrated that the product of this gene possessed both hemolytic and enterotoxic activities. These results showed that the enterotoxin of A. sobria possesses hemolytic activity. Nucleotide sequence determination of the toxin gene and amino acid sequence analysis of the purified toxin revealed that it is synthesized as a precursor composed of 488 amino acid residues, and that the 24 amino-terminal amino acid residues of the precursor is removed in the mature toxin. As antiserum against the purified toxin neutralized the fluid accumulation induced by living cells not only of A. sobria but also of A. hydrophila, this and antigenically related toxin(s) are thought to play an essential role in the induction of diarrhea by these organisms. The toxin-injured Chinese hamster ovary (CHO) cells induced the release of intracellular lactose dehydrogenase (LDH). The release of LDH from CHO cells and the lysis of erythrocytes by the toxin were repressed by the addition of dextran to the reaction solution, indicating that the toxin forms pores in the membranes and that the cells were injured by the osmotic gradient developed due to pore formation. However, the histopathological examination of intestinal cells exposed to the toxin showed that it caused fluid accumulation in the mouse intestinal loop without causing cellular damage.

Roles of macrophages in programmed cell death and remodeling of tail and body muscle of Xenopus laevis during metamorphosis

Examination was made of the involvement of macrophage phagocytosis in programmed cell death of tail and body muscle of the frog, Xenopus laevis, during metamorphosis by electron microscopy and immunohistochemical analysis. Electron microscopic observation revealed that macrophages were often found to be present in body and tail muscles at the most active stage of metamorphosis and to actively phagocytose apoptotic muscle fragments. Developmental changes in macrophages were examined using the macrophage-specific antibody, HAM56. Macrophages initially appeared in the early climax stage (stage 59), when the triiodothyronine (T3) level was high, increased rapidly during the process of muscle cell death, and assumed their greatest number at the late climax stage (stage 63/64). They decreased after stage 65/66, with a decrease in T3. Distribution and change in the number of macrophages were the same as those of muscle apoptotic bodies (sarcolytes) during metamorphosis, which suggests an interactive mechanism between macrophages and dying muscle cells. For clarification of this, study was made of the expression of HAM56 antigens that were X. laevis homologs of mouse attachmin, non-specific adhesion proteins in macrophages. The expression of HAM56 antigens in macrophages was found to increase with macrophage phagocytosis at the late climax stage, thus, macrophage differentiation would appear to take place during metamorphosis and HAM56 antigens may be essential for macrophage-dying muscle cell interactions.

Structural change and catalytic activity of horseradish peroxidase in oxidative polymerization of phenol

The effects of solvent and reaction conditions on the catalytic activity of horseradish peroxidase (HRP) were investigated for oxidative polymerization of phenol in water/organic mixtures using hydrogen peroxide as an oxidant. Also, the structural changes of HRP were investigated by CD and absorption spectroscopy in these solvents. The results suggest that the yield of phenol polymer (the conversion of phenol to polymer) is strongly affected by the reaction conditions due to the structural changes of HRP, that is, the changes in higher structure of the apo-protein and dissociation or decomposition of the prosthetic heme. Optimum solvent compositions for phenol polymerization depend on the nature of the organic solvents owing to different effects of the solvents on HRP structure. In addition to initial rapid changes, slower changes of HRP structure occur in water/organic solvents especially at high concentrations of organic solvents. In parallel with these structural changes, catalytic activity of HRP decreases with time in these solvents. At higher reaction temperatures, the yield of the polymer decreases, which is also ascribed to modification of HRP structure. It is known that hydrogen peroxide is an inhibitor of HRP, and the yield of phenol polymer is strongly dependent on the manner of addition of hydrogen peroxide to the reaction solutions. The polymer yield decreases significantly when hydrogen peroxide was added to the reaction solution in a large amount at once. This is probably due to inactivation of HRP by excess hydrogen peroxide. From the CD and absorption spectra, it is suggested that excess hydrogen peroxide causes not only decomposition of the prosthetic heme but also modification of the higher structure of HRP.

Synthesis and dehydrative condensation of square-planar mono- and dinuclear hydroxopalladium complexes with the hydrotris(3,5-diisopropylpyrazolyl)borato ligand (TpiPr2), TpiPr2(Py)Pd-OH, and (mu-OH)2[PdTpiPr2(H2O)]2

Mono- and dinuclear hydroxopalladium complexes (kappa 2-TpiPr2,X)(py)Pd-OH (1; X = H, Br) and (mu-OH)2[Pd(kappa 2-TpiPr2)(H2O)]2 (2) are prepared by base hydrolysis of the corresponding chloride complexes (kappa 2-TpiPr2,X)(py)Pd-Cl (3) and (mu-Cl)2[Pd(kappa 3-TpiPr2)]2 (4), respectively. Functionalization of the OH part in 1 is effected via dehydrative condensation with protic substrates (H-A) to give a series of substituted products, (kappa 2-TpiPr)(py)Pd-A (5), and treatment of the dinuclear complex 2 with excess acetic acid affords the mononuclear diacetato complex 6, (kappa 2-TpiPr2-H)Pd(OAc)2(HOAc). Complexes 1-4 and 6 have been characterized crystallographically, and it is revealed that complexes 2 and 6 involve cyclic hydrogen-bonding interaction among the nitrogen atom of the pendent noncoordinated pyrazolyl group, the hydrogen atom in the protic part of the ligand (OH, AcOH), and, in the case of 2, an external water molecule.

Involvement of tachykinin receptors in Clostridium perfringens beta-toxin-induced plasma extravasation

1 Clostridium perfringens beta-toxin causes dermonecrosis and oedema in the dorsal skin of animals. In the present study, we investigated the mechanisms of oedema induced by the toxin. 2 The toxin induced plasma extravasation in the dorsal skin of Balb/c mice. 3 The extravasation was significantly inhibited by diphenhydramine, a histamine 1 receptor antagonist. However, the toxin did not cause the release of histamine from mouse mastocytoma cells. 4 Tachykinin NK(1) receptor antagonists, [D-Pro(2), D-Trp(7,9)]-SP, [D-Pro(4), D-Trp(7,9)]-SP and spantide, inhibited the toxin-induced leakage in a dose-dependent manner. Furthermore, the non-peptide tachykinin NK(1) receptor antagonist, SR140333, markedly inhibited the toxin-induced leakage. 5 The leakage induced by the toxin was markedly reduced in capsaicin-pretreated mouse skin but the leakage was not affected by systemic pretreatment with a calcitonin gene-related peptide receptor antagonist (CGRP(8-37)). 6 The toxin-induced leakage was significantly inhibited by the N-type Ca(2+) channel blocker, omega-conotoxin MVIIA, and the bradykinin B(2) receptor antagonist, HOE140 (D-Arg-[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-bradykinin), but was not affected by the selective L-type Ca(2+) channel blocker, verapamil, the P-type Ca(2+) channel blocker, omega-agatoxin IVA, tetrodotoxin (TTX), the TTX-resistant Na(+) channel blocker, carbamazepine, or the sensory nerve conduction blocker, lignocaine. 7 These results suggest that plasma extravasation induced by beta-toxin in mouse skin is mediated via a mechanism involving tachykinin NK(1) receptors.

Visible-light-controlled homo- and copolymerization of styrenes by a bichromophoric Ir–Pd catalyst

Visible-light-controlled polymerization was achieved by a bichromophoric organopalladium catalyst which possesses a naphthyl-substituted cyclometallated Ir(iii) light-absorbing moiety.

The necessity of adjusting the dosage of zonisamide when coadministered with other anti-epileptic drugs

Zonisamide (ZNS), a new anti-epileptic drug that exhibits a wide anti-epileptic spectrum, is commonly prescribed concomitantly with other anti-epileptic drugs. The interaction between ZNS and other anti-epileptic drugs was investigated in epileptic patients. The steady state plasma levels of all the anti-epileptic drugs were measured by high-performance liquid chromatography. The concomitant administration of phenobarbital (PB), phenytoin (PHT), or carbamazepine (CBZ) with ZNS significantly decreased the ratio of the steady state plasma concentration to the administered dose (C/D ratio) of ZNS, whereas clonazepam (CZP) and valproic acid (VPA) when administered concomitantly with ZNS did not change the C/D ratio. Significant negative correlations were observed between the C/D ratio of ZNS and the doses of PB, PHT, CBZ, and VPA. On the other hand, the ratio of the plasma concentration of carbamazepine-10,11-epoxide (CBZ-E), the major active metabolite of CBZ, to the plasma concentration of CBZ was significantly decreased by concomitant administration with ZNS, indicating that ZNS inhibits the metabolism of CBZ. These findings show that when ZNS is administered concomitantly with these anti-epileptic drugs, it is necessary to monitor the plasma concentration of ZNS in order to adjust its dosage.

Pregnancy diagnosis based on the fecal progesterone concentration in beef and dairy heifers and beef cows

The present study was undertaken to examine whether pregnancy diagnosis was possible by measuring fecal progesterone concentrations in beef and dairy heifers and beef cows. Rectal fecal samples collected on days 18-24 after insemination or days 11-17 after embryo transfer were mixed with methanol and shaken for preparation of a fecal solution. After centrifugation, the supernatant was extracted with petroleum ether followed by an enzyme immunoassay for progesterone. All pregnant animals showed fecal progesterone concentrations greater than 50 ng/g of fecal material on days 18-24 after AI or estrus. In non-pregnant animals, however, the fecal progesterone concentrations ranged widely from 5 to 180 ng/g of fecal material. In non-pregnant cattle, the percentage of cattle with <50 ng progesterone/g of fecal material compared with the total number was 37-60% on days 18-20, whereas the percentages increased more than 70% to a maximum of 78.1% on day 23. When 50 ng/g was considered as the cut-off value, the sensitivity and specificity of positive pregnancy tests were less than 70% on days 21-24, and 100% for negative pregnancy tests on days 18-24. There were significant differences in the mean fecal progesterone concentrations between pregnant and non-pregnant cattle on days 19-24. These results suggest that feces can be utilized to substitute for plasma and milk to measure progesterone for the purpose of pregnancy diagnosis in heifers and cows.