Showing papers by "Kyoto University published in 1992"
TL;DR: The methodology for inducing dendritic cell growth that was recently described for mouse blood now has been modified to MHC class II- negative precursors in marrow, and this feature should prove useful for future molecular and clinical studies of this otherwise trace cell type.
Abstract: Antigen-presenting, major histocompatibility complex (MHC) class II-rich dendritic cells are known to arise from bone marrow. However, marrow lacks mature dendritic cells, and substantial numbers of proliferating less-mature cells have yet to be identified. The methodology for inducing dendritic cell growth that was recently described for mouse blood now has been modified to MHC class II-negative precursors in marrow. A key step is to remove the majority of nonadherent, newly formed granulocytes by gentle washes during the first 2-4 d of culture. This leaves behind proliferating clusters that are loosely attached to a more firmly adherent "stroma." At days 4-6 the clusters can be dislodged, isolated by 1-g sedimentation, and upon reculture, large numbers of dendritic cells are released. The latter are readily identified on the basis of their distinct cell shape, ultrastructure, and repertoire of antigens, as detected with a panel of monoclonal antibodies. The dendritic cells express high levels of MHC class II products and act as powerful accessory cells for initiating the mixed leukocyte reaction. Neither the clusters nor mature dendritic cells are generated if macrophage colony-stimulating factor rather than granulocyte/macrophage colony-stimulating factor (GM-CSF) is applied. Therefore, GM-CSF generates all three lineages of myeloid cells (granulocytes, macrophages, and dendritic cells). Since > 5 x 10(6) dendritic cells develop in 1 wk from precursors within the large hind limb bones of a single animal, marrow progenitors can act as a major source of dendritic cells. This feature should prove useful for future molecular and clinical studies of this otherwise trace cell type.
3,852 citations
TL;DR: The results suggest that activation of the PD‐1 gene may be involved in the classical type of programmed cell death.
Abstract: The classical type of programmed cell death is characterized by its dependence on de novo RNA and protein synthesis and morphological features of apoptosis. We confirmed that stimulated 2B4.11 (a murine T-cell hybridoma) and interleukin-3 (IL-3)-deprived LyD9 (a murine haematopoietic progenitor cell line) died by the classical type of programmed cell death. Assuming that common biochemical pathways might be involved in the deaths of 2B4.11 and LyD9, we isolated the PD-1 gene, a novel member of the immunoglobulin gene superfamily, by using subtractive hybridization technique. The predicted PD-1 protein has a variant form of the consensus sequence found in cytoplasmic tails of signal transducing polypeptides associated with immune recognition receptors. The PD-1 gene was activated in both stimulated 2B4.11 and IL-3-deprived LyD9 cells, but not in other death-induced cell lines that did not show the characteristic features of the classical programmed cell death. Expression of the PD-1 mRNA in mouse was restricted to the thymus and increased when thymocyte death was augmented by in vivo injection of anti-CD3 antibody. These results suggest that activation of the PD-1 gene may be involved in the classical type of programmed cell death.
2,616 citations
TL;DR: The molecular and functional diversity of the glutamate receptors is reviewed and their implications for integrative brain function are discussed.
Abstract: The glutamate receptors mediate excitatory neurotransmission in the brain and are important in memory acquisition, learning, and some neurodegenerative disorders. This receptor family is classified in three groups: the N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-kainate, and metabotropic receptors. Recent molecular studies have shown that many receptor subtypes exist in all three groups of the receptors and exhibit heterogeneity in function and expression patterns. This article reviews the molecular and functional diversity of the glutamate receptors and discusses their implications for integrative brain function.
2,588 citations
TL;DR: An expert system is reported for predicting localization sites of proteins only from the information on the amino acid sequence and the source origin, which is powerful and flexible enough to be used in genome analyses.
1,545 citations
TL;DR: Amino acid sequence and other molecular properties indicate that ascorbate peroxidase resembles cytochrome c peroxIDase from fungi rather than guaiacol per oxidase from plants, and it is proposed that the plant and yeast hydrogen peroxide-scavenging peroxidsases have the same ancestor.
Abstract: Ascorbate peroxidase is a hydrogen peroxide-scavenging enzyme that is specific to plants and algae and is indispensable to protect chloroplasts and other cell constituents from damage by hydrogen peroxide and hydroxyl radicals produced from it. In this review, first, the participation of ascorbate peroxidase in the scavenging of hydrogen peroxide in chloroplasts is briefly described. Subsequently, the phylogenic distribution of ascorbate peroxidase in relation to other hydrogen peroxide-scavenging peroxidases using glutathione, NADH and cytochrome c is summarized. Chloroplastic and cytosolic isozymes of ascorbate peroxidase have been found, and show some differences in enzymatic properties. The basic properties of ascorbate peroxidases, however, are very different from those of the guaiacol peroxidases so far isolated from plant tissues. Amino acid sequence and other molecular properties indicate that ascorbate peroxidase resembles cytochrome c peroxidase from fungi rather than guaiacol peroxidase from plants, and it is proposed that the plant and yeast hydrogen peroxide-scavenging peroxidases have the same ancestor.
1,504 citations
TL;DR: Three cDNA clones were isolated from a rat brain cDNA library by cross-hybridization with the cDNA for a metabotropic glutamate receptor to form a novel family of G protein-coupled receptors that differ in their signal transduction and expression patterns.
1,055 citations
12 May 1992
TL;DR: New control schemes of master-slave manipulators are proposed that provide the ideal kinesthetic coupling such that the operator can maneuver the system as though he/she were directly manipulating the remote object himself/herself.
Abstract: In this paper, the analysis and design of master-slave teleoperation systems are discussed. The goal of this paper is to build a superior master-slave system that can provide good maneuverability. We first analyze a one degree-of-freedom system including operator and object dynamics. Second, some ideal responses of master-slave systems are defined and a quantitative index of maneuverability is given, based on the concept of ideal responses. Third, we propose new control schemes of master-slave manipulators that provide the ideal kinesthetic coupling such that the operator can maneuver the system as though he/she were directly manipulating the remote object himself/herself. The proposed control scheme requires accurate dynamic models of the master and slave arms, but neither parameters of the remote object nor the operator dynamics is necessary. Finally, the proposed control scheme is introduced to a prototype master-slave system and the experimental results show the validity of the proposed scheme. >
953 citations
TL;DR: It is demonstrated that there is an additional mGLUR subtype which closely resembles mGluR1 in its signal transduction and pharmacological properties and is expressed in specialized neuronal cells in the central nervous system.
880 citations
TL;DR: In this article, it has been shown for various types of glasses and glass-ceramics that the essential condition for them to bond to living bone is the formation of an apatite layer on their surfaces in the body.
Abstract: It has been shown for various types of glasses and glass-ceramics that the essential condition for them to bond to living bone is the formation of an apatite layer on their surfaces in the body. CaO,SiO 2 -based glasses formed the surface apatite layer in a simulated body fluid, whereas CaO,P 2 O 5 -based glasses did not form it. This means that the rate of the apatite nucleation on the surfaces of the former glasses is much higher than that of the latter glasses. The increase in the degree of the supersaturation of the surrounding fluid with respect to the apatite due to dissolution of the calcium ion from the CaO,SiO 2 -based glasses was almost equal to that due to dissolution of the phosphate ion from the CaO,P 2 O 5 -based glasses. The high rate of the apatite nucleation on the surface of the former glasses is therefore attributed to the lower interface energy between the apatite and the glass surfaces. The CaO,SiO 2 -based glasses form a silica hydrogel on their surfaces prior to formation of the apatite layer. This means that the hydrated silica provides specific favorable sites for the apatite nucleation.
827 citations
TL;DR: The effects on ion selectivity of replacing lysine at position 1,422 in repeat III and/or alanine in repeat IV of rat sodium channel II are reported, suggesting that these residues constitute part of the selectivity filter of the channel.
Abstract: THE sodium channel, one of the family of structurally homologous voltage-gated ion channels1, differs from other members, such as the calcium and the potassium channels, in its high selectivity for Na+. This selectivity presumably reflects a distinct structure of its ion-conducting pore. We have recently identified two clusters of predominantly negatively charged amino-acid residues, located at equivalent positions in the four internal repeats of the sodium channel as the main determinants of sensitivity to the blockers tetrodotoxin and saxitoxin2. All site-directed mutations reducing net negative charge at these positions also caused a marked decrease in single-channel conductance2. Thus these two amino-acid clusters probably form part of the extracellular mouth and/or the pore wall of the sodium channel. We report here the effects on ion selectivity of replacing lysine at position 1,422 in repeat III and/or alanine at position 1,714 in repeat IV of rat sodium channel II (ref. 3), each located in one of the two clusters, by glutamic acid, which ccurs at the equivalent positions in calcium channels. These amino-acid substitutions, unlike other substitutions in the adjacent regions, alter ion-selection properties of the sodium channel to resemble those of calcium channels. This result indicates that lysine 1,422 and alanine 1,714 are critical in deter mining the ion selectivity of the sodium channel, suggesting that these residues constitute part of the selectivity filter of the channel.
752 citations
TL;DR: Results imply that the MDR1 gene could be activated during tumor progression associated with mutations in Ras and p53, and imply that drug resistance in human cancer is associated with overexpression of the multidrug resistance (MDR1) gene.
Abstract: Drug resistance in human cancer is associated with overexpression of the multidrug resistance (MDR1) gene, which confers cross-resistance to hydrophobic natural product cytotoxic drugs. Expression of the MDR1 gene can occur de novo in human cancers in the absence of drug treatment. The promoter of the human MDR1 gene was shown to be a target for the c-Ha-Ras-1 oncogene and the p53 tumor suppressor gene products, both of which are associated with tumor progression. The stimulatory effect of c-Ha-Ras-1 was not specific for the MDR1 promoter alone, whereas a mutant p53 specifically stimulated the MDR1 promoter and wild-type p53 exerted specific repression. These results imply that the MDR1 gene could be activated during tumor progression associated with mutations in Ras and p53.
TL;DR: The receptor selectivity of the natriuretic peptide family was investigated using the homologous assay system with endogenous ligands and receptors of the same species and the rank order of binding affinity for the C-receptor was ANP greater than CNP greater than BNP in both humans and rats.
Abstract: To elucidate the ligand-receptor relationship of the natriuretic peptide system, which comprises at least three endogenous ligands, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), and three receptors, the ANP-A receptor or guanylate cyclase-A (GC-A), the ANP-B receptor or guanylate cyclase-B (GC-B), and the clearance receptor (C-receptor), we characterized the receptor preparations from human, bovine, and rat tissues and cultured cells with the aid of the binding assay, Northern blot technique, and the cGMP production method. Using these receptor preparations, we examined the binding affinities of ANP, BNP, and CNP for the C-receptor and their potencies for cGMP production via the ANP-A receptor (GC-A) and the ANP-B receptor (GC-B). These analyses revealed the presence of a marked species difference in the receptor selectivity of the natriuretic peptide family, especially among BNPs. Therefore, we investigated the receptor selectivity of the natriuretic peptide family using the homologous assay system with endogenous ligands and receptors of the same species. The rank order of binding affinity for the C-receptor was ANP greater than CNP greater than BNP in both humans and rats. The rank order of potency for cGMP production via the ANP-A receptor (GC-A) was ANP greater than or equal to BNP much greater than CNP, but that via the ANP-B receptor (GC-B) was CNP greater than ANP greater than or equal to BNP. These findings on the receptor selectivity of the natriuretic peptide family provide a new insight into the understanding of the physiological and clinical implications of the natriuretic peptide system.
TL;DR: It is revealed that VIP receptor mRNA is widely distributed in neuronal cells of the adult rat brain, with a relatively high expression in the cerebral cortex and hippocampus, suggesting that they constitute a new subfamily of the Gs protein-coupled receptors.
TL;DR: The results suggest that cortisol and aldosterone are physiological substrates for P-glycoprotein in the human adrenal cortex and that substances that efficiently bind to P- glycoprotein are not necessarily transported by P- Glycoprotein.
TL;DR: The results suggest that HES-1 may play an important role in mammalian development by negatively acting on the two different sequences while Hes-3 acts as a repressor in a specific type of neurons.
Abstract: We report the molecular characterization of two novel rat helix-loop-helix (HLH) proteins, designated HES-1 and HES-3, that show structural homology to the Drosophila hairy and Enhancer of split [E(spl)] proteins, both of which are required for normal neurogenesis. HES-1 mRNA, expressed in various tissues of both embryos and adults, is present at a high level in the epithelial cells, including the embryonal neuroepithelial cells, as well as in the mesoderm-derived tissues such as the embryonal muscle. In contrast, HES-3 mRNA is produced exclusively in cerebellar Purkinje cells. HES-1 represses transcription by binding to the N box, which is a recognition sequence of E(spl) proteins. Interestingly, neither HES-1 nor HES-3 alone interacts efficiently with the E box, but each protein decreases the transcription induced by E-box-binding HLH activators such as E47. Furthermore, HES-1 also inhibits the functions of MyoD and MASH1 and effectively diminishes the myogenic conversion of C3H10T1/2 cells induced by MyoD. These results suggest that HES-1 may play an important role in mammalian development by negatively acting on the two different sequences while HES-3 acts as a repressor in a specific type of neurons.
TL;DR: In the developing rat brain, the level of mGluR1 expression gradually increased during early postnatal days in accordance with the maturation of neuronal elements.
Abstract: Distribution of the mRNA for a metabotropic glutamate receptor (mGluR1), which is linked to phosphoinositide (PI) hydrolysis, was investigated in adult and developing rat central nervous system (CNS) by in situ hybridization. Transcripts of mGluR1 were specifically localized to neurons and widely distributed throughout the adult rat brain. Most intensely labeled neurons were Purkinje cells of the cerebellum, mitral and tufted cells of the olfactory bulb, and neurons in the hippocampus, lateral septum, thalamus, globus pallidus, entopeduncular nucleus, ventral pallidum, magnocellular preoptic nucleus, substantia nigra, and dorsal cochlear nucleus. Moderately labeled neurons were seen in high density in the dentate gyrus, striatum, islands of Calleja, superficial layers of the retrosplenial, cingulate and entorhinal cortices, mammillary nuclei, red nucleus, and superior colliculus. In the developing rat brain, the level of mGluR1 expression gradually increased during early postnatal days in accordance with the maturation of neuronal elements.
These results show prominent expression of mGluR1 in the major targets of putative glutamatergic pathways and unique distribution pattern of mGluR1 distinct from those reported for ionotropic subtypes of glutamate receptors, suggesting specific roles of mGluR1 in the glutamatergic system. © 1992 Wiley-Liss, Inc.
TL;DR: It is shown that under appropriate assumptions on the latter mapping, any stationary point of the optimization problem is a global optimal solution, and hence solves the variational inequality problem.
Abstract: Whether or not the general asymmetric variational inequality problem can be formulated as a differentiable optimization problem has been an open question. This paper gives an affirmative answer to this question. We provide a new optimization problem formulation of the variational inequality problem, and show that its objective function is continuously differentiable whenever the mapping involved in the latter problem is continuously differentiable. We also show that under appropriate assumptions on the latter mapping, any stationary point of the optimization problem is a global optimal solution, and hence solves the variational inequality problem. We discuss descent methods for solving the equivalent optimization problem and comment on systems of nonlinear equations and nonlinear complementarity problems.
TL;DR: Pertussis toxin and phorbol ester produced distinct effects on the three transduction cascades, implying that mGluR1 independently links to the multiple transduction pathways probably through different G proteins.
TL;DR: The functions of the ETs, focusing especially on the molecular characteristics of their receptors, are discussed, involving at least two distinct subtypes of ET receptor.
TL;DR: CDNA transfection experiments suggest that alpha N-catenin is crucial not only for cadherin function but also for organization of multicellular structures.
TL;DR: In this article, the complete sequence of the liverwort mitochondrial DNA was determined and 94 possible genes in the sequence of 186,608 base-pairs were detected, including genes for three species of ribosomal RNA, 29 genes for 27 species of transfer RNA and 30 open reading frames (ORFs) for functionally known proteins.
TL;DR: 6 additional isoforms of the NMDA receptor generated via alternative splicing by molecular analysis of cDNA clones isolated from a rat forebrain cDNA library are reported, indicating that theNMDA receptor consists of heterogeneous molecules that differ in the extracellular sequence of the amino- and carboxyl-terminal regions.
TL;DR: The Judd-Ofelt intensity parameters, Ω, (t=2,4,6) for f-f transitions of Er 3+ ions doped in B 2 O 3 -R 2 O glasses were determined from optical-absorption measurements, and their compositional dependence was investigated systematically.
Abstract: The Judd-Ofelt intensity parameters, ${\mathrm{\ensuremath{\Omega}}}_{\mathit{t}}$ (t=2,4,6) for f-f transitions of ${\mathrm{Er}}^{3+}$ ions doped in ${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$-${\mathit{R}}_{2}$O (R=Na,K) glasses were determined from optical-absorption measurements, and their compositional dependence was investigated systematically. The values of ${\mathrm{\ensuremath{\Omega}}}_{2}$ exhibited a maximum around 25 mol % ${\mathit{R}}_{2}$O, while those of ${\mathrm{\ensuremath{\Omega}}}_{4}$ and ${\mathrm{\ensuremath{\Omega}}}_{6}$ decreased monotonically with an increase in ${\mathit{R}}_{2}$O content. The compositional dependences of ${\mathrm{\ensuremath{\Omega}}}_{4,6}$ were consistent with those of the isomer shift in $^{151}\mathrm{Eu}$ M\"ossbauer spectroscopy, which gives information about the 6s-electron density of ${\mathrm{Eu}}^{3+}$ ions. The variation of ${\mathrm{\ensuremath{\Omega}}}_{2}$ against ${\mathit{R}}_{2}$O content was related to the change in asymmetry of the rare-earth ligand due to the structural mixing of borate groups, while those of ${\mathrm{\ensuremath{\Omega}}}_{4,6}$ were related to the local basicity of rare-earth sites in the glass.
TL;DR: A functional cDNA clone encoding mouse EP2 subtype of prostaglandin (PG) E receptor was isolated from a mouse cDNA library by cross-hybridization with the mouse EP3 subtype PGE receptor cDNA, suggesting that this receptor is EP2Subtype.
TL;DR: The endothelial production of CNP is demonstrated and it is suggested that a member of the natriuretic peptide family may act as a local regulator in vascular walls, since evidence for the pathophysiological importance of the vascular renin-angiotensin system has been accumulating.
Abstract: C-type natriuretic peptide (CNP), the third member of the natriuretic peptide family, is thus far known to be distributed mainly in the central nervous system and is considered to act as a neuropeptide, in contrast to atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), which act as cardiac hormones. Recently, we and others have demonstrated that the ANP-B receptor, which is selectively activated by CNP, is localized not only in the central nervous system but in peripheral tissues, including blood vessels. This finding has made us speculate regarding the peripheral production of CNP. In the present study, cultured endothelial cells were examined for CNP production by RIA and Northern blot analysis. CNP-like immunoreactivity was detected in the conditioned media of endothelial cells. Northern blot analysis detected CNPmRNA with a size of 1.2 kb. In addition, transforming growth factor (TGF)-beta, one of the key growth factors for vascular remodeling, markedly stimulated the expression of CNPmRNA and induced a tremendous increase in CNP secretion. We could also detect CNP transcript in the bovine thoracic aorta using the reverse transcription-polymerase chain reaction method. The present study demonstrates the endothelial production of CNP and suggests that a member of the natriuretic peptide family may act as a local regulator in vascular walls. Since evidence for the pathophysiological importance of the vascular renin-angiotensin system has been accumulating and the natriuretic peptide system is known to be antagonistic to the renin-angiotensin system, the possible existence of "vascular natriuretic peptide system" may prove to be of physiological and clinical relevance.
TL;DR: The results suggest that v-src-mediated tyrosine phosphorylation perturbs cadherin function directly or indirectly, and the inhibition of tyrosines phosphorylated restores cadher in action to the normal state.
Abstract: Rat 3Y1 cells acquire metastatic potential when transformed with v-src, and this potential is enhanced by double transformation with v-src and v-fos (Taniguchi, S., T. Kawano, T. Mitsudomi, G. Kimura, and T. Baba. 1986. Jpn. J. Cancer Res. 77:1193-1197). We compared the activity of cadherin cell adhesion molecules of normal 3Y1 cells with that of v-src transformed (SR3Y1) and v-src and v-fos double transformed (fosSR3Y1) 3Y1 cells. These cells expressed similar amounts of P-cadherin, and showed similar rates of cadherin-mediated aggregation under suspended conditions. However, the aggregates or colonies of these cells were morphologically distinct. Normal 3Y1 cells formed compacted aggregates in which cells are firmly connected with each other, whereas the transformed cells were more loosely associated, and could freely migrate out of the colonies. Overexpression of exogenous E-cadherin in these transformed cells had no significant effect on their adhesive properties. We then found that herbimycin A, a tyrosine kinase inhibitor, induced tighter cell-cell associations in the aggregates of the transformed cells. In contrast, vanadate, a tyrosine phosphatase inhibitor, inhibited the cadherin-mediated aggregation of SR3Y1 and fosSR3Y1 cells but had little effect on that of normal 3Y1 cells. These results suggest that v-src-mediated tyrosine phosphorylation perturbs cadherin function directly or indirectly, and the inhibition of tyrosine phosphorylation restores cadherin action to the normal state. We next studied tyrosine phosphorylation on cadherins and the cadherin-associated proteins, catenins. While similar amounts of catenins were expressed in all of these cells, the 98-kD catenin was strongly tyrosine phosphorylated only in SR3Y1 and fosSR3Y1 cells. Cadherins were also weakly tyrosine phosphorylated only in the transformed cells. The tyrosine phosphorylation of these proteins was enhanced by vanadate, and inhibited by herbimycin A. Thus, the tyrosine phosphorylation of the cadherin-catenin system itself might affect its function, causing instable cell-cell adhesion.
TL;DR: In this paper, a comparison between the transition-metal 2p spectra and atomic-multiplet calculations is used to determine the 3d count of holes induced by substitution for both series are located in states of mixed metal 3d--oxygen 2p character.
Abstract: The controlled-valence properties of ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{FeO}}_{3}$ and ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ are studied by means of soft-x-ray absorption spectroscopy. A comparison between the transition-metal 2p spectra and atomic-multiplet calculations is used to determine the 3d count. The O 1s spectrum is used to characterize changes in unoccupied states that contain oxygen p character. The results indicate that the holes induced by substitution for both series are located in states of mixed metal 3d--oxygen 2p character. The ground state of ${\mathrm{LaFeO}}_{3}$ is mainly 3${\mathit{d}}^{5}$ and becomes 3${\mathit{d}}^{5}$L (where L denotes a ligand hole) in the ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{FeO}}_{3}$ series for low Sr concentration. The main component of the ground state of ${\mathrm{LaMnO}}_{3}$ is 3${\mathit{d}}^{4}$ and becomes a mixture of 3${\mathit{d}}^{3}$ and 3${\mathit{d}}^{4}$L in the ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ series. The trends in controlled- valence properties of similar oxides across the transition-metal series can be rationalized within the framework of the Zaanen-Sawatzky-Allen model.
TL;DR: The finding of many inhibitors of ADP- ribosyltransferases, especially poly(ADP-ribose) synthetase, supports the view that ADp-ribosylation of proteins may be regulated by a variety of metabolites or structural constituents in the cell.
TL;DR: In this paper, a pure hydrated silica gel can induce apatite formation on its surface in simulated body fluid when its starting pH is increased from 7.2 to 7.4.
Abstract: It has been confirmed that the essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body. It has been proposed that a hydrated silica formed on the surfaces of these materials in the body plays an important role in forming the surface apatite layer, but this has not yet been proved. In the present study, it is shown experimentally that a pure hydrated silica gel can induce apatite formation on its surface in a simulated body fluid when its starting pH is increased from 7.2 to 7.4.
TL;DR: Ascorbate is photoregenerated in the thylakoids from the MDA radicals produced in a reaction of asCorbate peroxidase for the scavenging of hydrogen peroxide.
Abstract: Ascorbate peroxidase, a key enzyme for the scavenging of hydrogen peroxide in chloroplasts, was found in a thylakoid-bound form in spinach chloroplasts at comparable activity to that in the stroma. The activity of peroxidase was detectable in the thylakoids only when prepared by an ascorbate-containing medium, and enriched in the stroma thylakoids. The thylakoid enzyme was not released from the membranes by either 2 mM EDTA, 1 M KC1, 2 M NaBr or 2 M NaSCN, but was solubilized by detergents. Enzymatic properties of the thylakoid-bound ascorbate peroxidase were very similar to those of the stromal ascorbate peroxidase. Thylakoid-bound ascorbate peroxidase could scavenge the hydrogen peroxide either added or photoproduced by the thylakoids. No photoreductio n of hydrogen peroxide was observed, however, in the thylakoids whose ascorbate peroxidase was inhibited by KCN and thiol reagents or inactivated by the treatment with ascorbate-depletion. The primary oxidation product of ascorbate in a reaction of ascorbate peroxidase, monodehydroascorbate (MDA) radical, was photoreduced in the thylakoids, as detected by the quenching of chlorophyll fluorescence, disappearance of EPR signals of the MDA radicals and the MDA radical-induced oxygen evolution. Thus, ascorbate is photoregenerated in the thylakoids from the MDA radicals produced in a reaction of ascorbate peroxidase for the scavenging of hydrogen peroxide.