Taxonomic study of the genusMyagropsis (Cystoseiraceae,Phaeophyta)

The generic names of the brown algaeMyagropsis, Cystoseira andCystophyllum have been used in Japan, Korea and China for a small group of seaweeds whose limits have not been clearly understood. Studies on the development of the eggs and subsequent germlings show that substantial differences occur betweenCystoseira andMyagropsis. Myagropsis Kützing is distinguished fromCystoseira C. Agardh by the following characteristics: (1) the tongue cell is undivided during development of the conceptacle; (2) paraphyses are projected from the conceptacle ostiole and become entangled; (3) during development, oospore germlings are mixed among paraphyses projecting from the ostiole; (4) oospores are large, with eight nuclei at maturity; (5) thirty-two primary rhizoids are produced on the germlings; and (6) the thallus is bilateral in organization. The shape and size of vesicles, their formation, and the presence of cryptostomata have been used as specific characters, but their use cannot be continued. It is concluded that the genusMyagropsis is monotypic, with a single species,M. myagroides (Turner) Fensholt. The status of this species is also discussed.     

Expression of human atrial natriuretic polypeptide gene in Cos 7 cells

Cos 7 cells transfected with human atrial natriuretic polypeptide (hANP) gene with SV40 enhancer and replication origin sequences expressed hANP gene. The expressed RNA was indistinguishable from native hANP mRNA and the transcribed protein seemed to be properly processed to alpha-hANP and beta-hANP. This system provides a useful approach to investigate the processing of hANPs and the structure-function relationship of amino acid sequences of hANPs.     

Reduction in antiviral activity of human interferon-gamma in acidic media with reference to structural change

The fluorescence intensity of a unique tryptophan 36 in human interferon-gamma was drastically decreased below pH 4 with a concomitant decrease of antiviral activity. The region of residues 32-42 of human interferon-gamma was found by calculation to have a low hydrophobicity together with a high helical hydrophobic moment, and the net electric charge of this region having an amphiphilic helical structure changed significantly near pH 4. These results suggest that the region of residues 32-42 plays an important role in exhibiting antiviral activity.     

Augmentation of the generation of cell-mediated cytotoxicity in culture by mitomycin C

Summary The effects of mitomycin C (MMC) on the generation of cell-mediated cytotoxicity in primary stimulation culture of human peripheral blood mononuclear cells (PBM) with the B lymphoblastoid Raji cell line were assessed. The cell-mediated cytotoxicity induced in culture was significantly augmented when MMC was added to cultures on day –1 to day 3 for 24 h at concentrations of 2.5×10^–2 g/ml and 2.5×10^–3 g/ml. To identify the cell populations affected by MMC, PBM were separated by adherence to plastic after treatment with MMC for 24 h (day –1). The two populations were recombined with untreated separated cells and stimulated with antigen. The ability to develop an augmented cell-mediated cytotoxicity was associated with the adherent cell fraction of MMC-treated PBM. Therefore, the ability of MMC-treated adherent cells to produce interleukin 1 (IL 1) was examined. Significantly higher levels of IL 1 were produced by treated cells as compared to untreated adherent cells. The results appear to indicate that the selective effects of MMC on the adherent cell fraction, especially the modification of IL 1 production, may be involved in the mechanisms of MMC-induced augmented cell-mediated cytotoxicity.     

Blocking action of Nephila clavata spider toxin on ionic currents activated by glutamate and its agonists in isolated hippocampal neurons

The blocking action ofNephila clavata spider neurotoxin, or JSTX, on ionic currents activated by L-glutamate and its agonists when applied to the membrane of neurons isolated from the rat hippocampus was investigated using a concentration clamp technique. Crude JSTX venom was found to block L-glutamate-, quisqualate, and kainate-activated ionic currents induced by activating non-N-methyl-D-aspartate (non-NMDA) membrane receptors. Following the effects of JSTX, ionic currents activated by L-glutamate and its agonists declined to 34–36% of their initial value with no recovery during JSTX washout. An active fraction of JSTX at concentrations of 10^–4–10^–5 produced almost total but partially reversible blockade of ionic currents. The action of JSTX became less effective during depolarization. The concentration dependence of JSTX-induced blockade of kainate-activated ionic currents was investigated and the velocity constants of interaction between the toxin and glutamate receptors obtained. It is postulated that JSTX interacts with chemically-operated non-NMDA ionic channels, blocking their transition into a number of their possible open states.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 152–160, March–April, 1989.     

Role of MgATP and MgADP in the cross-bridge kinetics in chemically skinned rabbit psoas fibers. Study of a fast exponential process (C)

The role of the substrate (MgATP) and product (MgADP) molecules in cross-bridge kinetics is investigated by small amplitude length oscillations (peak to peak: 3 nm/cross-bridge) and by following amplitude change and phase shift in tension time courses. The range of discrete frequencies used for this investigation is 0.25-250 Hz, which corresponds to 0.6-600 ms in time domain. This report investigates the identity of the high frequency exponential advance (process C), which is equivalent to "phase 2" of step analysis. The experiments are performed in maximally activated (pCa 4.5-5.0) single fibers from chemically skinned rabbit psoas fibers at 20 degrees C and at the ionic strength 195 mM. The rate constant 2 pi c deduced from process (C) increases and saturates hyperbolically with an increase in MgATP concentration, whereas the same rate constant decreases monotonically with an increase in MgADP concentration. The effects of MgATP and MgADP are opposite in all respects we have studied. These observations are consistent with a cross-bridge scheme in which MgATP and MgADP are in rapid equilibria with rigorlike cross-bridges, and they compete for the substrate site on myosin heads. From our measurements, the association constants are found to be 1.4 mM-1 for MgATP and 2.8 mM-1 for MgADP. We further deduced that the composite second order rate constant of MgATP binding to cross-bridges and subsequent isomerization/dissociation reaction to be 0.57 x 10(6)M-1s-1.     

Conformation of guanosine 5'-diphosphate as bound to a human c-Ha-ras mutant protein: a nuclear Overhauser effect study

1H NMR spectra of a GDP/GTP-binding domain of human c-Ha-ras gene product (residues 1-171) in which glutamine-61 was replaced by leucine [ras(L61/1-171) protein] were analyzed. By one-dimensional and two-dimensional homonuclear Hartmann-Hahn spectroscopy and nuclear Overhauser effect (NOE) spectroscopy of the complex of the ras(L61/1-171) protein and GDP, the ribose H1', H2', H3', and H4' proton resonances of the bound GDP were identified. The guanine H8 proton resonance of the bound GDP was identified by substituting [8-2H]GDP for GDP. The dependences of the H1' and H8 proton resonance intensities on the duration of irradiation of the H1', H2', H3', and H8 protons were measured. By numerical simulation of these time-dependent NOE profiles, the conformation of the protein-bound GDP was elucidated; the guanosine moiety takes the anti form about the N-glycosidic bond with a dihedral angle of chi = -124 +/- 2 degrees and the ribose ring takes the C2'-endo form. Such an analysis of the conformation of a guanine nucleotide as bound to a GTP-binding protein will be useful for further studies on the molecular mechanism of the conformational activation of ras proteins on ligand substitution of GDP with GTP.     

Transformation of chicken embryo fibroblast cells by avian retroviruses containing the human Fyn gene and its mutated genes.

The transforming activity of the human fyn protein, p59fyn, which is a kinase of the src family, was investigated by testing the effect of recombinant avian retrovirus (Fyn virus) expressing p59fyn on chickens or cultured chicken embryo fibroblast (CEF) cells. The Fyn virus did not induce transformed foci. After several passages of the virus stock on CEF cells, however, a few foci were detected in the presence of dimethyl sulfoxide. Chickens inoculated with Fyn virus at the stage of 12-day-old embryos developed fibrosarcomas 3 to 6 weeks after hatching. The viruses obtained from these foci and from one of the tumor tissues showed high transforming activity in the presence of dimethyl sulfoxide, suggesting that these viruses carry spontaneous mutations of the fyn gene. Four fyn genes from CEF DNAs infected with transforming viruses were molecularly cloned, and their products were confirmed to possess transforming activity. DNA sequence analysis of the fyn genes showed that two of the four mutants have Thr instead of Ile at position 338 in the kinase domain. The other two mutants carry deletions of 78 and 108 base pairs, respectively, which result in complete loss of region C of SH2. The overall level of proteins containing phosphotyrosine was significantly higher in transformed cells than in normal CEF cells. Our data indicate that when expressed at high levels in a retrovirus, normal p59fyn cannot cause cellular transformation, but that mutant p59fyn with either a single amino acid substitution in the kinase domain or a deletion including region C produces a transforming protein, perhaps due to enhanced tyrosine kinase activity. This is the first observation that deletion of region C can unmask the potential transforming activity of a src family kinase.     

Flavonoids inhibit the expression of heat shock proteins

Cells exposed to several forms of stress, such as heat shock, transiently synthesize a group of proteins called heat shock proteins (hsps). Although many stressors other than heat shock are known to induce hsps, inhibitors of hsp expression have never been reported. Here we show that quercetin and several other flavonoids inhibit the synthesis of hsps induced by heat shock in two human cell lines, Hela cells and COLO320 DM cells. Quercetin inhibited the induction of hsp70 at the level of mRNA accumulation. This is the first report to describe the inhibition of hsp expression by reagents.