Comparative analysis of strategies to prepare electron sinks in aquatic photoautotrophs

Photosynthesis Research - While subject to illumination, photosystem I (PSI) has the potential to produce reactive oxygen species (ROS) that can cause photo-oxidative damage in oxygenic...     

Enzymatic synthesis of hydrophilic undecylenic acid sugar esters and their biodegradability

To enhance water solubility of 10-undecylenic acid, which has anti-fungus, anti-bacterial and anti-virus activity, d-glucose, trehalose and sucrose were regioselectively esterified with vinyl 10-undecylenic acid ester in dimethyl formamide by a commercial protease, Bioprase conc., from Bacillus subtilis. 6-O-(10-Undecylenoyl) d-glucose, 6-O-(10-undecylenoyl) trehalose and 1-O-(10-undecylenoyl) sucrose were obtained. The influence of structural variation by changing the sugar moiety was analyzed the surface tension and biodegradability.     

Enzymatic synthesis of trehalose esters having lipophilicity

To improve trehalose lipophilicity, trehalose was regioselectively esterified with vinyl fatty acid esters in dimethyl formamide by protease from Bacillus subtilis to give 6-O-lauroyltrehalose, 6-O-myristoyltrehalose, 6-O-palmitoyltrehalose, 6-O-stearoyltrehalose, 6-O-oleoyltrehalose and 6-O-linoleoyltrehalose. The influence of structural variation by changing fatty acid substitute was examined by measurement of the surface tension and biodegradability.     

Dissection of respiratory and cyclic electron transport in Synechocystis sp. PCC 6803

Cyclic electron transport (CET) is an attractive hypothesis for regulating photosynthetic electron transport and producing the additional ATP in oxygenic phototrophs. The concept of CET has been established in the last decades, and it is proposed to function in the progenitor of oxygenic photosynthesis, cyanobacteria. The in vivo activity of CET is frequently evaluated either from the redox state of the reaction center chlorophyll in photosystem (PS) I, P700, in the absence of PSII activity or by comparing PSI and PSII activities through the P700 redox state and chlorophyll fluorescence, respectively. The evaluation of CET activity, however, is complicated especially in cyanobacteria, where CET shares the intersystem chain, including plastoquinone, cytochrome b₆/f complex, plastocyanin, and cytochrome c₆, with photosynthetic linear electron transport (LET) and respiratory electron transport (RET). Here we sought to distinguish the in vivo electron transport rates in RET and CET in the cyanobacterium Synechocystis sp. PCC 6803. The reduction rate of oxidized P700 (P700⁺) decreased to less than 10% when PSII was inhibited, indicating that PSII is the dominant electron source to PSI but P700⁺ is also reduced by electrons derived from other sources. The oxidative pentose phosphate (OPP) pathway functions as the dominant electron source for RET, which was found to be inhibited by glycolaldehyde (GA). In the condition where the OPP pathway and respiratory terminal oxidases were inhibited by GA and KCN, the P700⁺ reduction rate was less than 1% of that without any inhibitors. This study indicate that the electron transport to PSI when PSII is inhibited is dominantly derived from the OPP pathway in Synechocystis sp. PCC 6803.

     

Transgenic rats overexpressing the human MrgX3 gene show cataracts and an abnormal skin phenotype

The human MrgX3 gene, belonging to the mrgs/SNSRs (mas related genes/sensory neuron specific receptors) family, was overexpressed in transgenic rats using the actin promoter. Two animal lines showed cataracts with liquification/degeneration and swelling of the lens fiber cells. The transient epidermal desquamation was observed in line with higher gene expression. Histopathology of the transgenic rats showed acanthosis and focal parakeratosis. In the epidermis, there was an increase in cellular keratin 14, keratin 10, and loricrin, as well as PGP 9.5 in innervating nerve fibers. These phenotypes accompanied an increase in the number of proliferating cells. These results suggest that overexpression of the human MrgX3 gene causes a disturbance of the normal cell-differentiation process.     

Susceptibility of plasma lipids to peroxidation

Lipid peroxidation is an old and yet novel subject. It induces membrane disturbance and damage and its products are known to induce the generation of various cytokines and cell signaling. In the present work, the susceptibility and specificity of human plasma lipids to oxidation were studied, aiming specifically at elucidating the effects of oxidation milieu and oxidants. Cholesteryl esters (CEs) and phosphatidylcholines (PCs) were more readily oxidized in plasma than in organic solution under similar conditions. The susceptibilities of PC and free cholesterol (FC) relative to CE to free radical-mediated lipid peroxidation induced by peroxyl radicals and peroxynitrite were smaller in plasma than in organic solution. The higher rate of CE oxidation by free radicals than PC may be accounted for by the physical effects as well as higher content of polyunsaturated lipids in CE than PC. On the contrary, PC was more readily oxidized than CE by lipoxygenases. The lipid hydroperoxides were stable in organic solution but reduced to the corresponding hydroxides in plasma, the rate being much faster for PC hydroperoxides than for CE and FC hydroperoxides. It was confirmed that free radical-mediated oxidation gave both cis,trans and trans,trans, racemic, random hydroperoxides, while that by lipoxygenase gave only regio- and stereo-specific cis,trans-hydroperoxide.     

Characterization of transgenic rats constitutively expressing vitamin D-24-hydroxylase gene

Vitamin D-24-hydroxylase (CYP24) is one of the enzymes responsible for vitamin D metabolism. CYP24 catalyzes the conversion of 25-hydroxyvitamin D(3) [25(OH)D(3)] to 24,25-dihydroxyvitamin D(3) [24,25(OH)(2)D(3)] in the kidney. CYP24 is also involved in the breakdown of 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)], the active form of vitamin D(3). In this study, we generated transgenic (Tg) rats constitutively expressing CYP24 gene to investigate the biological role of CYP24 in vivo. Surprisingly, the Tg rats showed a significantly low level of plasma 24,25(OH)(2)D(3). Furthermore, the Tg rats developed albuminuria and hyperlipidemia shortly after weaning. The plasma lipid profile revealed that all lipoprotein fractions were elevated in the Tg rats. Also, the Tg rats showed atherosclerotic lesions in the aorta, which greatly progressed with high-fat and high-cholesterol feeding. These unexpected results suggest that CYP24 is involved in functions other than the regulation of vitamin D metabolism.     

Quantification of NAD(P)H in cyanobacterial cells by a phenol extraction method

Photosynthesis Research - Plants in their natural environment are often exposed to fluctuating light because of self-shading and cloud movements. As changing frequency is a key characteristic of...     

Identification and characterization of a novel UDP-GalNAc:GlcAbeta-R alpha1,4-N-acetylgalactosaminyltransferase from a human sarcoma cell line.

We recently discovered a novel alpha-N-acetylgalactosaminyltransferase in fetal bovine serum (Kitagawa et al., J. Biol. Chem., 270, 22190-22195, 1995) and also in mouse mast cytoma cells (Lidholt et al., Glycoconjugate J., 14, 737-742, 1997), which catalyzed the transfer of an alpha-GalNAc residue to the linkage tetrasaccharide-serine, GlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-O-Ser, derived from proteoglycans. In this study, we characterized this enzyme using a preparation obtained from the serum-free culture medium of a human sarcoma (malignant fibrous histiocytoma) cell line by phenyl-Sepharose chromatography. Structural characterization by1H NMR spectroscopy of the reaction product using the linkage tetrasaccharide-serine, GlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-O-Ser, as a substrate demonstrated that the enzyme was a UDP-GalNAc:GlcAbeta1-R alpha1,4-N -acetylgalactosaminyltransferase. This is the first identification of an alpha1,4-N-acetylgalactosaminyltransferase. Using N -acetylchondrosine GlcAbeta1-3GalNAc as an alternative substrate, the enzyme required divalent cations for the transferase reaction, with maximal activity at 20 mM Mn2+and exhibited a dual optimum at pH 6.5 and pH 7.4 depending upon the buffers used, with the highest activity in a 50 mM 2-( N -morpholino)ethanesulfonic acid buffer at pH 6.5. The apparent Km values obtained for N -acetylchondrosine, the linkage tetrasaccharide-serine, and UDP-GalNAc were 1060 microM, 188 microM, and 27 microM, respectively. This suggested that the linkage tetrasaccharide-serine was a good acceptor substrate for the enzyme. In addition, the enzyme utilized glucuronylneolactotetraosylceramide GlcAbeta1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4G lcbeta1-1Cer but not sulfoglucuronylneolactotetraosylceramide GlcA(3-O -sulfate)beta1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4Gl cbeta1-1Cer as acceptor substrates. The possibility of involvement of this enzyme in the biosynthesis of glycosaminoglycan as well as other GlcA-containing glycoconjugates is discussed.     

Respiration accumulates Calvin cycle intermediates for the rapid start of photosynthesis in Synechocystis sp. PCC 6803

We tested the hypothesis that inducing photosynthesis in cyanobacteria requires respiration. A mutant deficient in glycogen phosphorylase (?GlgP) was prepared in Synechocystis sp. PCC 6803 to suppress respiration. The accumulated glycogen in ΔGlgP was 250–450% of that accumulated in wild type (WT). The rate of dark respiration in ΔGlgP was 25% of that in WT. In the dark, P700⁺ reduction was suppressed in ΔGlgP, and the rate corresponded to that in (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone)-treated WT, supporting a lower respiration rate in ?GlgP. Photosynthetic O₂-evolution rate reached a steady-state value much slower in ?GlgP than in WT. This retardation was solved by addition of d-glucose. Furthermore, we found that the contents of Calvin cycle intermediates in ?GlgP were lower than those in WT under dark conditions. These observations indicated that respiration provided the carbon source for regeneration of ribulose 1,5-bisphosphate in order to drive the rapid start of photosynthesis.