Electron Flow from NAD(P)H Dehydrogenase to Photosystem I is Required for Adaptation to Salt Shock in the Cyanobacterium Synechocystis sp. PCC 6803

The role of the NAD(P)H-dehydrogenase complex in adaptationto salt stress was examined in an ndhB-inacti-vated mutant ofthe cyanobacterium Synechocystis sp. PCC 6803. Wild-type cellsand ndhB-inactivated mutant cells grew at similar rates underconditions of low salinity (<0.6M NaCl) and high CO² (3%).However, when the concentration of NaCl in the culture mediumwas higher than 0.6 M, the mutant cells grew much more slowlythan the wild-type cells. Upon addition of high concentrationsof NaCl, the oxygen-evolving activity was rapidly inhibitedbut then it recovered, with the rate of recovery depending onthe concentration of NaCl. The recovery of the mutant cellswas significantly delayed when the concentration of NaCl wasabove 0.3 M. At 0.9 M NaCl, wild-type cells recovered with ahalf time of about 40 min, while mutant cells did not recover.The kinetics of changes in Chi fluorescence confirmed theseresults. In wild-type cells, input of electrons from the cytosolto PSI via the NAD(P)H-dehy-drogenase complex increased uponsalt shock. It appears, therefore, that the electron flow fromthe cytosol to PSI via NAD(P)H-dehydrogenase is essential forthe adaptation of cyanobacteria to salt shock. (Received June 11, 1997; Accepted September 24, 1997)     

Allelic variants of the human MHC class I chain-related B gene (MICB)

 The human major histocompatibility complex (MHC) is located within a 4 megabase segment on chromosome 6p21.3. Recently, a highly divergent MHC class I chain-related gene family, MIC was identified within the class I region. The MICA and MICB genes in this family have unique patterns of tissue expression. The MICA gene is highly polymorphic, with more than 20 alleles identified to date. To elucidate the extent of MICB allelic variations, we sequenced exons 2 (α1), 3 (α2), 4 (α3), and 5 (transmembrane) as well as introns 2 and 4 of this gene in 46 HLA homozygous B-cell lines. We report the identification of eleven alleles based on seven non-synonymous, two synonymous, and four intronic nucleotide variations. Interestingly, one allele has a nonsense mutation resulting in a premature termination codon in the α2 domain. Thus, MICB appears to have fewer alleles than MICA, not unlike the allelic ratio between the HLA-C and -B loci. A preliminary linkage analysis of the MICB alleles with those of the closely located MICA and HLA-B genes revealed no conspicuous linkage disequilibrium between them, implying the presence of a potential recombination hotspot between the MICB and MICA genes. Received: 16 April 1997 / Revised: 19 May 1997     

Enzymatic synthesis of peptide in acetonitrile/supercritical carbon dioxide

Summary The peptide synthesis from N-acetyl-L-tyrosine ethyl ester (Ac-Tyr-OEt) and amino acid amides was realized using -chymotrypsin (CT) in acetonitrile (MeCN) or acetonitrile/supercritical carbon dioxide (SCCO₂) containing small amounts of water. In both solvent systems there was an optimum water content for peptide synthesis, above which peptide hydrolysis became more important. After an incubation for 5 hours, the yields of the peptide was 64% in MeCN and 91% in MeCN/SCCO₂, respectively.     

Permeabilization of the Plasma Membrane and Maintenance of the Integrity of Organelles in Higher Plant Cells

Plasma membranes of cells isolated from higher plant were permeabilizedby a combination of plasmolysis and deplasmolysis in the presenceof EGTA. Permeabilized cells, with intact vacuoles, could beseparated from intact cells by density gradient centrifugation.The evolution of oxygen in permeabilized cells was measuredin the presence of PGA. (Received February 20, 1992; Accepted May 25, 1992)     

NAD(P)H Dehydrogenase-Dependent Cyclic Electron Flow around Photosystem I in the Cyanobacterium Synechocystis PCC 6803: a Study of Dark-Starved Cells and Spheroplasts

Electron donation to P700⁺ through plastoquinone in the intersystemchain from both respiratory substrates and the photoreductantsin PSI has been shown to be mediated by the NAD(P)H-dehydrogenasecomplex (NDH) in Synechocystis PCC 6803 cells [Mi et al. (1992)Plant Cell Physiol. 33: 1233]. To confirm the participationof NDH in the cyclic electron flow around PSI, the redox kineticsof P700 and Chi fluorescence were analyzed in cells rendereddeficient in respiratory substrates by dark starvation and inspheroplasts. Dark-starved cells showed a high steady-state level of P700⁺under far-red (FR) illumination and the plastoquinone pool wasin a highly oxidized state. An NDH-defective mutant consistentlyshowed a high level of P700 oxidation under FR before and afterthe dark starvation. Donation of electrons either from exogenousNADPH or from photoreduced NADPH⁺ to the intersystem chain viaplastoquinone was demonstrated using spheroplasts from wild-typecells, but not those from the NDH-defective mutant, as monitoredby following changes in the kinetics of Chi fluorescence andthe redox state of P700. The electron flow to PSI via plastoquinone,mediated by NADPH, was sensitive to rotenone, Hg²⁺ ions and2-thenoyltrifluoroacetone, inhibitors of mitochondrial NDH andsuccinate dehydrogenase, but not to antimycin A. The pool sizeof electrons that can be donated to P700⁺ from the cytosol throughthe intersystem chain increased with increasing duration ofillumination time by actinic light and was sensitive to rotenonein both wild-type cells and spheroplasts, but no such resultswere obtained in the NDH-defective mutant of Synechocystis 6803.The results support our previous conclusion that NDH is a mediatorof both respiratory electron flow and cyclic electron flow aroundPSI to the intersystem chain in the cyanobacterium Synechocystis. (Received August 20, 1993; Accepted November 22, 1993)     

Unique after-hyperpolarization accompanying action potential inChara globularis

A unique after-hyperpolarization was found in internodal cells ofChara globularis. The cells generated an ordinary action potential due to regenerative depolarization induced by the outward electric current pulse larger than a threshold stimulus. After reaching a depolarizing peak, the membrane potential repolarized and overshooted the resting potential to a value which was somehow 40 mV more negative than the resting potential before stimulation (after-hyperpolarization). Since the membrane resistance increased during the after-hyperpolarization, the after-hyperpolarization is thought to be caused by an increase in the resistance (decrease in the conductance) of the passive diffusion channel.     

Comparative analyses on food habits of Japanese marten,Siberian weasel and leopard cat in the Tsushima islands,Japan

Food habits of three sympatric carnivore mammals in the Tsushima islands of Japan were studied during 1986–91. Scats of the Tsushima marten (n=1236), the Siberian weasel (n=218) and the Tsushima leopard cat (n=350) were collected monthly and the food items were determined by scat contents analysis. Marten was omnivorous showing a high level of diversity of food throughout the year. The important foods for marten were fruits and berries from spring to autumn, insects in summer and autumn and small mammals all year round. Leopard cat preferred to hunt wood/mice and birds, and remained a flesh meat specialist throughout the year. Weasel was intermediate between marten and leopard cat, but was slightly biased towards the flesh meat eater. The three carnivores do not compete against one another for food, except for small rodents. A conflict for food between leopard cat and weasel was suggested to be more intense than that of other combinations based on diet overlapping. Marten may be characterized as an opportunistic generalist. When interspecific competitors existed, or human disturbance to the habitat occurred, the preferential flexibility of the marten to alternative food resources might become more advantageous than the other two species.