Photosynthetic activities of a thermophilic blue-green alga

Photosynthetic activities of a thermophilic blue-green alga,a species of Synechococcus, were studied with special referenceto its growth at high temperatures. A rapid algal growth occurredin the temperature range between 50 and 60?C, showing the maximumrate, six doublings per day, at about 57?C. Photosynthetic oxygenevolution and methyl viologen photoreduction in the cells werealso active at high temperatures and the optimum temperaturesfor these activities agreed with that of the algal growth. Thegrowth and photosynthetic activities were very low at room temperatureand irreversibly inactivated at temperatures above 60?C. The thylakoid membranes isolated from the alga were also photochemicallyactive at high temperatures. The membranes mediated ferricyanidephotoreduction coupled with a stoichiometric oxygen evolutionat a rate comparable to that of photosynthetic oxygen evolutionin the cells. The optimum temperature for the reaction was ashigh as 50?C. The membranes also showed a photosystem I-mediatedreaction at high temperatures. These observations indicate thatthe thylakoid membranes are intrinsically thermophilic in thisorganism. Thus the growth of the alga at high temperatures canbe well correlated to thermophilic properties of the photosyntheticapparatus. (Received February 20, 1978; )     

Effects of dibromothymoquinone and bathophenanthroline on flash-induced cytochrome f oxidation in spinach chloroplasts

The effects of several electron transport inhibitors on themagnitude and kinetics of cytochrome f oxidation induced byflash illumination were studied in the - and -band regions.On the flash excitation only a fraction of cytochrome f presentin the chloroplasts was oxidized with a half time of 0.1 to0.3 msec and then reduced with a half time of 10 to 25 msec. Dibromothymoquinone (DBMIB) at concentrations which severelysuppressed the reduction of cytochrome f approximately doubledthe magnitude of cytochrome f oxidation caused by a flash, mainlyby inducing an additional slow oxidation of cytochrome f witha half time longer than 1 msec. Enhancement of the cytochromef oxidation was also observed in the presence of bathophenanthroline.Such enhanced oxidation in duced by the two inhibitors was largelydiminished with the addition of reduced 2,6-dichlorophenolindophenolwhich accelerated cytochrome f reduction. In contrast, the inhibitionof cytochrome f reduction by 3-(3,4-dichlorophenyl)-1,1-dimethylurea(DCMU) was not associated with an increase in the magnitudeof cytochrome f oxidation. However, addition of DBMIB to theDCMU-poisoned chloroplasts enhanced cytochrome f oxidation,suggesting that this is related to a block of the electron transportbetween plastoquinone and cytochrome f. The results are explainedby assuming the occurrence of an electron carrier between plastoquinoneand cytochrome f. (Received May 10, 1978; )     

Scanning electron microscopy of giemsa-stained chromosomes and surface-spread chromosomes

Giemsa-stained chromosomes as prepared for light microscopy, and including G-banded, C-banded, and FPG-stained chromosomes, were examined by scanning electron microscopy. Although suitable for light microscopy, these chromosomes were too flat for a close examination of their fine structure by scanning electron microscopy. The surface of Giemsa-positive regions was rough and bright, whereas that of unstained or poorly stained regions was smoother and less bright. Giemsa-staining, therefore, seems to produce the bulkiness of the chromosomes. On topographical examination by scanning electron microscopy, the transparent chromosomes as observed with the light microscope proved to be footprints. Stereographical examinations of surface-spread chromosomes showed that minimally stretched chromosomes were composed of a mass of nodular and twisted looping fibers with an average diameter of about 300 Å. The substructure of these chromosome fibers was not determined. The kinetochore region was discernible as a constriction in the mass of the chromosome fibers, and was distinguishable from gaps by the presence of several chromosome fibers parallel to the axis of the chromatid. The organization of the chromosome fibers, however, was disordered rather than regular.     

The conformational stability and flexibility of insulin with an additional intramolecular cross-link

The conformational stability and flexibility of insulin containing a cross-link between the alpha-amino group of the A-chain to the epsilon-amino group of Lys29 of the B-chain was examined. The cross-link varied in length from 2 to 12 carbon atoms. The conformational stability was determined by guanidine hydrochloride-induced equilibrium denaturation and flexibility was assessed by H2O/D2O amide exchange. The cross-link has substantial effects on both conformational stability and flexibility which depend on its length. In general, the addition of a cross-link enhances conformational stability and decreases flexibility. The optimal length for enhanced stability and decreased flexibility was the 6-carbon link. For the 6-carbon link the Gibbs free energy of unfolding was 8.0 kcal/mol compared to 4.5 kcal/mol for insulin, and the amide exchange rate decreased by at least 3-fold. A very short cross-link (i.e. the 2-carbon link) caused conformational strain that was detectable by a lack of stabilization in the Gibbs free energy of unfolding and enhancement in the amide exchange rate compared to insulin. The effect of the cross-link length on insulin hydrodynamic properties is discussed relative to previously obtained receptor binding results.     

Insulin binds to type V collagen with retention of mitogenic activity

The abilities of eight extracellular matrix proteins, fibronectin, vitronectin, laminin, and collagen types I, II, III, IV, and V to bind insulin were examined by binding studies with insulin conjugated with peroxidase. At a physiological pH and ionic strength, type V collagen bound to insulin most strongly. The other types of collagen, laminin, and vitronectin also bound insulin with affinity lower than that of type V collagen. The insulin-binding site of type V collagen was in a 30-kDa CNBr fragment of the alpha 1 (V) chain. Analysis of the amino acid sequence showed that this 30-kDa fragment was identical to the heparin-binding fragment of type V collagen. The insulin-binding sites of laminin and vitronectin were located in the A chain and in the heparin-binding domain, respectively. Insulin bound to type V collagen stimulated the synthesis of DNA by mouse mammary tumor MTD cells, indicating that bound insulin retained mitogenic activity.     

Molecular structure of the Japanese hepatitis C viral genome

The amino acid sequence of the polyprotein deduced from the nucleotide sequence of the Japanese hepatitis C virus genome (N. Kato et. al. (1990) Proc. Natl. Acad. Sci. USA 87, 9524–9528)indicated that this virus is a member of a new class of positive-stranded RNA viruses. Several domains of this polyprotein also showed weak homology with those of flaviviruses and pestiviruses including the chymotrypsin-like serine proteinase. NTPase and RNA-dependent RNA polymerase     

Multiple Neurite Formation in Neuroblastoma Cell Lines by Griseolic Acid, a Potent Inhibitor of Cyclic Nucleotide Phosphodiesterases

The morphological change of several neuroblastoma cell lines induced by griseolic acid, a novel and potent inhibitor of cyclic nucleotide phosphodiesterase (PDE), was examined. In the cell lines tested, Neuro-2a (a murine neuroblastoma cell line) showed dose-dependent (1 microM-1 mM) neurite extension. Griseolic acid markedly increased the intracellular cyclic AMP level of Neuro-2a cells, suppressed DNA synthesis (82% at 1 mM), and induced multipolar (multiple-neurite-bearing)-type neuritogenesis. A similar type of neurite outgrowth was induced by 8-bromo-cyclic AMP, which also elevated the intracellular cyclic AMP concentration. In contrast, when Neuro-2a cells were treated with retinoic acid, neurite formation was of the monopolar (single-neurite-bearing) type. Papaverine and theophylline, which have been frequently used as PDE inhibitors, failed to induce these morphological changes up to 1 mM, probably owing to the lesser potency of these compounds as compared with griseolic acid on the inhibition of PDE. Retinoic acid, theophylline, and papaverine were ineffective at elevating the intracellular cyclic AMP level. These results suggest that multipolar-type cell shape change in Neuro-2a cells is correlated with the accumulation of intracellular cyclic AMP and that griseolic acid is a useful compound to induce neuroblastoma cells into terminal differentiation.     

Presence of transplantable T-lymphoid cells in C57BL/6 mice infected with murine AIDS virus.

The Duplan strain of murine leukemia virus induces murine AIDS in C57BL/6 mice. When spleen cells from C57BL/6 mice infected with the virus were transplanted into nude mice, subcutaneous solid tumors at the transplanted sites were formed and splenomegaly and lymphadenopathy were induced. These transplantable cells were Thy-1- CD4+ alpha-beta T-cell receptor-positive T cells and integrated with the pathogenic defective viral genome. These results indicate that neoplastic cells of T-cell lineage were induced by infecting C57BL/6 mice with murine AIDS virus.     

Possible influence of lysophospholipase on the production of 1-acyl-2-acetylglycerophosphocholine in macrophages.

The rate of production of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (PAF) and 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (acylPAF) was measured in macrophages following the incorporation of [3H]acetate. Upon activation by A23187, guinea pig alveolar macrophages incorporated [3H]acetate into PAF, but a little radioactivity was found in acylPAF. However, labeling of acylPAF and PAF with [3H]acetate was greatly enhanced in A23187-stimulated alveolar macrophages that had been pretreated with phenylmethanesulphonyl fluoride (PMSF). [3H]PAF was predominantly converted to 1-[3H]alkyl-2-acyl glycerophosphocholine, but [14C]acylPAF rapidly hydrolyzed to 14C-labeled free fatty acid by the incubation with lysates prepared from macrophages. The deacetylation of [14C]acylPAF and [3H]PAF by acetylhydrolase and also the hydrolysis of [14C]lysoPC by lysophospholipase were strongly inhibited in macrophages that had been pretreated with PMSF, while PMSF failed to inhibit the activities of acetyltransferase and acyltransferase. The relative proportions of PAF and acylPAF were quite different in different types of cells. In contrast to alveolar macrophages, peritoneal macrophages, neutrophils and spleen cells from guinea pigs incorporated 2-4 times more [3H]acetate into acylPAF than into PAF. The presence of high levels of acylPAF in peritoneal macrophages was confirmed by GLC-MS analysis. The activities of lysophospholipase, acetylhydrolase and acetyltransferase were measured in alveolar and peritoneal macrophages to determine whether the preferential formation of acylPAF as compared to PAF in peritoneal macrophages was due to differences in these activities between alveolar and peritoneal macrophages. The activity of acetylhydrolase of peritoneal macrophages was almost the same as that in alveolar macrophages. The activity of acetyltransferase in peritoneal macrophages was about half of that in alveolar macrophages. However, the activity of lysophospholipase in peritoneal macrophages was one-sixth of that in alveolar macrophages. These results suggest that lysophospholipase is one of the primary factors involved in the control of the production of acylPAF in activated cells, and that it acts by modulating the availability of lysoPC for the synthesis of acylPAF. Furthermore, high levels of activity of lysophospholipase allow the preferential formation of PAF, via the rapid hydrolysis of lysoPC which would act as a competitive inhibitor of the incorporation of acetate into lysoPAF.     

Conformations of dibucaine and tetracaine in small unilamellar phosphatidylcholine vesicles as studied by nuclear Overhauser effects in 1H nuclear magnetic resonance spectroscopy.

Conformations of dibucaine and tetracaine in small unilamellar phosphatidylcholine vesicles have been investigated by nuclear Overhauser effects (NOEs) in 1H nuclear magnetic resonance spectroscopy. Two-dimensional NOE and chemical exchange correlated spectroscopy (NOESY) and rotating frame NOE spectroscopy (ROESY) methods have been applied for obtaining the NOEs. In the NOESY spectra, NOEs between protons within the drug were overwhelmed by spin diffusion even at a short mixing time. This observation reduced the usefulness of the NOESY method on the one hand, however, on the other hand it facilitated remarkably in revealing signals due to the drug, hidden in the broad resonances of the membranes. In the ROESY spectra, the spin diffusion phenomena were less effective; accordingly the conformations of the drugs interacting with membranes were determined by the ROESY method. The observed NOE data showed that dibucaine takes more than two conformations and that both dibucaine and tetracaine are present as a dimer in the membranes. Molecular dynamics calculations supported these findings.