Isolation of a Putative Carboxysomal Carbonic Anhydrase Gene from the Cyanobacterium Synechococcus PCC7942

The Type II mutants of the cyanobacterium Synechococcus PCC7942 (G.D. Price, M.R. Badger [1989] Plant Physiol 91: 514-525) are able to accumulate a large pool of inorganic carbon inside the cell, but are unable to utilize it for CO(2) fixation, resulting in a high CO(2)-requiring phenotype. We have isolated a 3.5-kb BamHI clone (pT2) that complements the Type II mutants, and complementation analysis with DNA subclones indicated that the complementing region was located in the 0.75-kb XhoI-Bg/II fragment. This same region hybridized to the chloroplastic carbonic anhydrase (CA) gene from spinach on Southern blots and to a mRNA of approximate 1 kb on northern blots. Restriction mapping and sequence analysis revealed that pT2 is the same as a genomic clone (pBM3.8) that complements another high CO(2)-requiring (temperature sensitive) mutant, C3P-O (E. Suzuki, H. Fukuzawa, S. Miyachi [1991] Mol Gen Genet 226: 401-408). Recently, a 272-amino acid open reading frame showing 22% homology with pea and spinach chloroplast CA genes was identified in clone pBM3.8 (H. Fukuzawa, E. Suzuki, Y. Komukal, S. Miyachi [1992] Proc Natl Acad Sci USA 89: 4437-4441). CA activity was detected in Escherichia coli cells transformed with subclones of pT2 (pT2-A and pT2-A1) containing the HindIII-Bg/II fragment, and the expressed CA has properties similar to those of the CA activity associated with carboxysomes purified from Synechococcus PCC7942 (G.D. Price, J.R. Coleman, M.R. Badger [1992] Plant Physiol 100: 784-793). Therefore, it is reasonable to conclude that the HindIII-Bg/II fragment codes for the carboxysomal CA gene product. The result is discussed in the context of the role that carboxysomal CA plays in the operation of the CO(2)-concentrating mechanism in cyanobacteria.

Expression of c-fos, c-jun and jun B in peripheral blood lymphocytes from young and elderly adults

The expression of c-fos, c-jun and jun B proto-oncogenes was studied in phytohemagglutinin (PHA) activated peripheral blood lymphocytes (PBL) from young and aged humans. Specific mRNAs for c-fos and c-jun were detectable within 30 min after cell activation and reached maximal levels within 2 h. Both c-fos and jun B mRNAs decreased to pre-activation levels within 6 h, while c-jun mRNA remained elevated. In PHA-activated PBL, no age-related differences were observed in c-fos or jun B mRNA expression. However, c-jun mRNA levels decreased significantly (1.73 +/- 0.08 vs. 1.16 +/- 0.09 arbitrary units, P < 0.01, young vs. old) in PBL from elderly individuals activated with PHA. Because previous work has demonstrated that T cells from elderly individuals may display normal proliferative responses when activated via the anti-CD2 pathway, c-jun and jun B mRNA expression was also studied in anti-CD2-activated purified T cells. No age-related differences were found in the expression of either of these two proto-oncogenes by anti-CD2 activated T cells. These results suggest that the decreased IL-2 production and proliferative response displayed by PHA-activated PBL from elderly adults may be related to age-related changes in c-jun mRNA expression and in the ratio of c-fos to c-jun mRNA.

Dependency plots suggest the kinetic structure of ion channels

Ion channels are integral membrane proteins that regulate ionic flux through cell membranes by opening and closing (gating) their pores. The gating can be monitored by observing step changes in the current flowing through single channels, and analysis of the observed open and closed interval durations has provided a window to develop kinetic models for the gating process. One difficulty in developing such models has been to determine the connections (transition pathways) among the various kinetic states involved in the gating. To help overcome this difficulty we present a transform (dependency plot) of the single-channel data that can give immediate insight into the connections. A dependency plot is derived by calculating a contingency table from a two-dimensional (joint density) dwell-time distribution of adjacent open and closed intervals by assuming that the two classified criteria are the open and closed durations of each pair of adjacent intervals. A three-dimensional surface plot of the fractional difference between the numbers of observed interval pairs and the numbers expected if the durations of adjacent intervals are independent then gives the dependency plot. An excess of interval pairs in the dependency plot suggests that the open and closed states (or compound states) that give rise to the interval pairs in excess are directly connected. A deficit of interval pairs suggests that the open and closed states (or compound states) that give rise to the interval pairs in deficit are either not directly connected or that there are additional open-closed transition pathways arising from the directly connected states.

Nerve growth factor receptor gene expression in human peripheral blood lymphocytes in aging

Nerve growth factor (NGF) has a modulating effect on immune function, which may occur as a consequence of binding to the NGF receptor (NGF-R). To determine if mRNA for the gene coding for p75NGFR (low affinity NGF-R) is present in lymphocytes, Northern blot analysis of mRNA from human peripheral blood lymphocytes (PBL) and purified T lymphocytes was initiated using cDNA probe for human p75NGFR. p75NGFR mRNA was present in PBL and T lymphocytes, and the mRNA in response to phytohemagglutinin stimulation showed maximum levels at 14 hr of stimulation. p75NGFR mRNA content when analyzed in PBL and T cells from volunteers of various ages showed that p75NGFR mRNA expression does not change with the age of the cell donor.

Chronic lithium treatment impairs phosphatidylinositol hydrolysis in membranes from rat brain regions

Membranes prepared from rat brain regions were used to measure the receptor-coupled and/or guanine nucleotide-binding protein (G protein)-mediated hydrolysis of exogenous [3H]phosphatidylinositol ([3H]PI). Guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and NaF (in the presence of AlCl3) caused concentration-dependent stimulations of [3H]PI hydrolysis, supporting the conclusion that G proteins mediating [3H]PI hydrolysis can be activated in this preparation. Neither of these responses was altered by in vitro incubation with 8 mM LiCl, but both were reduced in hippocampal, striatal, and cortical membranes from rats that had been treated with lithium for 4 weeks compared with controls. Two cholinergic agonists, carbachol and pilocarpine, induced no hydrolysis of [3H]PI unless GTP gamma S was also present, in which case each equally stimulated [3H]PI hydrolysis above that obtained with GTP gamma S alone. In the presence of GTP gamma S several excitatory amino acid agonists stimulated [3H]PI hydrolysis to an extent similar to that of carbachol. After chronic lithium treatment, [3H]PI hydrolysis stimulated by carbachol was significantly attenuated, but the response to quisqualate was unaffected. Therefore, lithium added in vitro does not have an effect on cholinergic receptor- or G protein-mediated [3H]PI hydrolysis, but each of these is reduced by chronic lithium treatment. Because exogenous [3H]PI was provided as the substrate, it is evident that the inhibitory effect of chronic lithium treatment cannot be due to substrate depletion. Impaired function of G proteins appears to be the most likely mechanism accounting for attenuated [3H]PI hydrolysis after chronic administration of lithium.

Spinal distribution of extracellular field potentials generated by electrical stimulation of pudendal and perineal afferents in the cat

Electrical stimulation of sensory pudendal and superficial perineal nerves evokes focal synaptic potentials produced by activation of spinal neurons in the lumbosacral gray matter in chloralose anesthetized or decerebrate cats. The field potentials evoked by sensory pudendal nerve stimulation were located in medial parts of laminae V and VI, and lamina X in the S1 to S3 spinal segments. The superficial perineal cutaneous field potentials partially overlapped with those produced by the pudendal nerve, but in general were localized more laterally in laminae V and VI. The central latencies of the earliest portion of the field potentials evoked by either sensory pudendal or superficial perineal nerves were less than 0.9 ms suggesting that monosynaptic activation of neurons contributed to the potentials.

Adrenalectomy potentiates immediate early gene expression in rat brain

Administration of kainate or pentylenetetrazole increased c-fos, c-jun, junB, and junD mRNA levels in rat brain in a dose-dependent manner. Kainate increased these mRNA levels predominantly in the hippocampus, and pentylenetetrazole was more effective in the cortex. Adrenalectomy (3 days) was used to eliminate endogenous glucocorticoid hormones. Adrenalectomy significantly potentiated kainate-induced increases, compared with increases caused by kainate (4 mg/kg) alone, in the hippocampal mRNA levels of c-fos and junB by 6.5-fold and of junD by twofold and tended to augment c-jun mRNA. Corticosterone administration blocked the potentiated stimulation of these mRNA levels caused by adrenalectomy. Adrenalectomy also significantly increased pentylenetetrazole-induced levels of c-fos mRNA in the cortex. These results demonstrate that glucocorticoids modulate immediate early gene expression in the brain, raising the possibility that this interaction contributes to interneuronal and interindividual differences in responses to stimuli and to the effects of stress- or disease-induced changes in glucocorticoid concentrations.

Adrenalectomy increases phosphoinositide hydrolysis induced by norepinephrine or excitatory amino acids in rat hippocampal slices

Phosphoinositide hydrolysis induced by norepinephrine, quisqualate, or trans-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD), but not by carbachol, was approximately 50% greater in hippocampal slices from adrenalectomized (14 days) rats compared with controls. These changes appeared to be selective for the hippocampus because no effects of adrenalectomy on phosphoinositide hydrolysis were detected in cortical or striatal slices. The enhanced response to norepinephrine in hippocampal slices after adrenalectomy was observed throughout the effective concentration range of norepinephrine, was not influenced by in vitro addition of corticosterone, was not mimicked or altered by incubation with dibutyryl cyclic adenosine 3',5'-monophosphate (AMP), and did not appear to be due to impaired inhibition of the response to norepinephrine which was elicited by activation of protein kinase C or by inclusion of an inhibitory concentration of quisqualate. These findings indicate that adrenalectomy either removes an inhibitory influence of glucocorticoids on the phosphoinositide system in the hippocampus or that the neurodegeneration of granule cells in the dentate gyrus following adrenalectomy is associated with neurotransmitter-selective increases in phosphoinositide hydrolysis. These data provide further evidence that glucocorticoids modify signal transduction in the brain and extends their known influence to the phosphoinositide second messenger system.

Inositol trisphosphate, cyclic AMP, and cyclic GMP in rat brain regions after lithium and seizures

The mechanism of action of lithium, the primary treatment for bipolar affective disorder, is unknown but may involve inhibition of second messenger production in the brain. Therefore, the concentrations of three second messengers, inositol 1,4,5 trisphosphate (Ins 1,4,5P3), cyclic adenosine monophosphate (AMP), and cyclic guanosine monophosphate (GMP), were measured in rat cerebral cortex and hippocampus after acute or chronic lithium administration, as well as after treatment with the cholinergic agonist pilocarpine alone or in combination with lithium at a dose that induces seizures only in lithium pretreated rats. Neither acute nor chronic lithium treatment altered the hippocampal or cortical concentration of Ins 1,4,5P3, cyclic AMP, or cyclic GMP. Pilocarpine administered alone increased Ins 1,4,5P3 in both regions, did not alter cyclic AMP, and slightly increased cyclic GMP in the cortex. Coadministration of lithium plus pilocarpine caused large increases in the concentrations of all three second messengers and the production of each of them was uniquely attenuated: lithium reduced pilocarpine-induced increases of Ins 1,4,5P3 in the cortex at 60 min; chronic lithium administration reduced stimulated cyclic AMP production in the hippocampus; and chronic lithium treatment impaired stimulated cyclic GMP production in both regions. In summary, chronic lithium treatment appeared only to reduce Ins 1,4,5P3 and cyclic AMP concentrations after a long period of stimulation whereas cyclic GMP production was reduced by chronic lithium administration after both short and long periods of stimulation. Thus cyclic GMP was most sensitive to lithium and lithium attenuation of second messenger formation may be most important in excessively activated pathways.

Infection of cord blood monocyte-derived macrophages with human immunodeficiency virus type 1

We have investigated the susceptibility of cord blood monocyte-derived macrophages to human immunodeficiency virus type 1 (HIV-1) infection in vitro. Cord blood monocytes were maintained in vitro for 10 to 15 days and then infected with HIV-1. Syncytia were observed 14 days after infection by light microscopy. Viral proteins were detected by immunofluorescence assay. Electron microscopic examination demonstrated typical lentivirus particles within cytoplasmic vacuoles. The supernatants from the HIV-1-infected cultures also contained significant reverse transcriptase activity and p24 antigen. Like adult monocyte/macrophages, cord-derived monocyte/macrophages expressed the CD4 receptor molecule. Pretreatment with blocking antibody prior to infection with HIV-1 Bal significantly reduced or blocked infection of cord monocyte/macrophages. When cord and adult monocyte/macrophages were infected with HIV-1 Bal or Ada-M and directly compared, higher reverse transcriptase activities and p24 antigen expression were obtained with cord monocyte/macrophages. However, no significant difference was found between adult and cord monocyte/macrophages infected with HIV-1 IIIB. These observations suggest that cord monocyte-derived macrophages may be important in the pathogenesis of pediatric AIDS and that the increased susceptibility of cord monocyte/macrophages to HIV-1 infection in vitro may be relevant to the enhanced susceptibility of neonates to HIV-1 diseases in vivo.

Effect of ethidium on the torsion constants of linear and supercoiled DNAs

The torsion elastic constants (alpha) of linear pBR322 (4363 bp) and pUC8 (2717 bp) DNAs and supercoiled pBR322 and pJMSII (4375 bp) DNAs are measured in 0.1 M NaCl as a function of added ethidium/base-pair (EB/BP) ratio by studying the fluorescence polarization anisotropy (FPA) of the intercalated ethidium. The time-resolved FPA is measured by using a picosecond dye laser for excitation and time-correlated single photon counting detection. Previously developed theory for the emission anisotropy is generalized to incorporate rotations of the transition dipole due to excitation transfer. The excitation transfers are simulated by a Monte Carlo procedure (Genest et al., Biophys. Chem. 1 (1974) 266-278) and the consequent rotations of the transition dipole are superposed on the Brownian rotations. After accounting for excitation transfer, the torsion constants of the linear DNAs are found to be essentially independent of intercalated ethidium up to a binding ratio r = 0.10 dye/bp. Dynamic light scattering measurements on linear pUC8 DNA confirm that the torsion constant is independent of binding ratio up to r = 0.20 dye/bp. If alpha d denotes the torsion constant between ethidium and a base-pair, and alpha 0 that between two base-pairs, then our data imply that alpha d/alpha 0 lies in the range 0.65 to 1.64 with a most probable value of 1.0. The torsion constants of supercoiled DNAs decrease substantially with increasing binding ratio even after accounting for excitation transfer. At the binding ratio r* = 0.064, where the superhelix density vanishes and superhelical strain is completely relaxed, the torsion constant of the supercoiled pBR322 DNA/dye complex lies below that of the corresponding linear DNA/dye complex by about 30%. This contradicts the conventional view according to which linear, nicked circular, and supercoiled DNA/dye complexes with r = r* should coexist with the same concentration of free dye, display the same distribution of bound dye, and exhibit identical secondary structures, twisting and bending rigidities, and FPA dynamics. These and other observations imply the existence of metastable secondary structure in freshly relaxed supercoiled DNAs. A tentative explanation is presented for these and other unexpected observations on supercoiled DNAs.

Observation of DNA molecules undergoing capillary electrophoresis

This paper presents a method to observe the motions and configurations of large DNA molecules undergoing capillary electrophoresis (CE). A simple device to perform CE horizontally under microscopic observation is designed and images of single DNA molecules inside the capillary are obtained using an epi-fluorescence microscope. DNA molecules moved towards the negative electrode when an electric field was applied. The mobilities of three types of DNA (T4 and lambda bacteriophage DNA and PBR322 plasmid DNA) were measured at different electric field strength. The mobility vs. electric field strength curves of these three large DNAs showed that the mobility remained constant at high electric field strength (200-600 Volt/cm) and increased significantly at low electric field strength (less than or equal to 50 Volt/cm.). The apparent mobilities of the large DNA molecules were independent of molecular weight. At electric field strengths greater than or equal to 400 Volt/cm., big aggregates (snowballs) of DNA molecules formed and moved upstream towards the positive electrode. When the field was turned off, the aggregates dissociated into a cloud of single DNA molecules, and diffused into the solution.

Do women with premenstrual symptoms self-medicate with caffeine?

Recent investigations have suggested that caffeine consumption is related to the occurrence and severity of premenstrual symptoms. Phillis has proposed that not only the total amount of caffeine consumed but also the pattern of consumption over the menstrual cycle may be important. This study explored whether women who experience moderate or severe premenstrual symptoms differ from other women in their pattern of caffeine intake throughout the menstrual cycle. Analysis of data for 96 complete menstrual cycles from 47 women demonstrated that caffeine intake during the menstrual cycle differed between women who experience moderate or severe premenstrual symptoms and other women. Furthermore, the monthly pattern of caffeine consumption for women with moderate or severe premenstrual symptoms, but not for other women, differed substantially from Phillis's proposed beneficial pattern. Women with premenstrual symptoms may self-mediate with caffeine in response to premenstrual symptoms, thereby exacerbating their symptoms.

Unhooking dynamics of U-shaped DNA molecule undergoing gel electrophoresis

It has been found that DNA molecules are often hooked around obstacles in a U-shaped configuration in gel electrophoresis. To understand the dynamics of the unhooking of U-shaped DNA molecules undergoing gel electrophoresis, we have examined the length changes of the longer and shorter arms of the U-shape as a function of time. Two types of unhooking have been found. In one type, the length changes of both arms are expontential in time but with different time constants. In another type, the length changes of the shorter arm is exponential and that of the longer one is linear with time. The interpretation is that the extent of stretch of the spring-like DNA chain decreases as the length difference between the two arms increases during the unhooking processes, and that the frictions at the pivot point can be relatively large depending upon the local structure of the gel. The friction coefficient at the pivot point is estimated to be nu 0 = (2.98 +/- 1.42)x10(-5) g/sec.

Dynamic light scattering from weakly bending rods: estimation of the dynamic bending rigidity of the M13 virus

A theory is presented for the dynamic structure factor [S(K,t]) of weakly bending rods. This treatment is based on a discrete bead model for the Brownian dynamics in which all bead motions associated with bending are constrained to occur in a plane perpendicular to the end-to-end vector, thus prohibiting extension or contraction along that axis. Preset hydrodynamic interactions are incorporated in a numerically exact manner. The predicted normalized dynamic structure factor S(K,t)/S(K,0) should be valid for short times t such that the rms rotation of the end-to-end vector around any transverse axis is much less than 1.0 radian. With geometrical parameters appropriate for the M13 virus, the intensity autocorrelation function G(2) (K,t) = 1 + magnitude of S(K,t)/S(K,0)2 is calculated over a range of times and scattering vectors K for selected values of the persistence length P. The calculated G(2) (K,t) are fitted to a single exponential with unit baseline over the same range of times as the experimental photon correlation functions, and the apparent diffusion coefficients Dapp (K) are obtained from the best-fit relaxation times. For the sake of completeness, an exact expression is derived for the apparent diffusion coefficient obtained from the initial slope of the dynamic structure factor. However, this does not reduce to the known correct result in the rigid rod limit. To obtain the correct result, the limit of infinite bending rigidity must be taken before the limit of zero time. For this and other reasons, the initial slope value of Dapp (K) is not useful for weakly bending rods. Photon correlation functions are measured for the M13 virus, which is virtually identical to the often-studied fd virus. The experimental photon correlation functions are fitted over 8 relaxation times to a single-exponential plus baseline, and the Dapp (K) are calculated from the best-fit relaxation times. Theoretical curves of Dapp (K) vs K2 for selected values of P are compared with the experimental data, which are satisfactorily reproduced when P = 22000 +/- 2000 A. This dynamic value is close to the static value, P = 20000 +/- 2000 A, reported for the very similar fd virus. The most recent theories of Maeda and Fujime and their dynamic light scattering studies of fd virus are compared with the present results in some detail. Their optimum value of P is in surprisingly good agreement with the present value.

[Toxic principles of Oxytropis glabra DC]

Eight alkaloids were isolated from Oxytropis glabra and identified as anagirine, thermopsine, N-methylcytisine, sparteine, baptifoline, adenine, dictamnine and ethyl allophanate respectively by spectral analysis and physicochemical methods. All these alkaloids were isolated from this genus for the first time and ethyl allophanate was found in nature for the first time.

Analysis of the convulsant-potentiating effects of lithium in rats

Lithium pretreatment of rats has previously been shown to potentiate the convulsant effects of cholinomimetic drugs, such as pilocarpine. The first objective of this project was to determine if lithium also potentiates seizures induced by other classes of drugs. Lithium pretreatment of rats did not affect seizure activity induced by administration of N-methyl-D-aspartate, kainic acid, bicuculline, or pentylenetetrazole. This suggests that the proconvulsant effect of lithium is largely selective for cholinomimetics. A second series of experiments investigated possible mechanisms of the lithium potentiation of pilocarpine-induced seizures. The alpha 2-adrenergic receptor agonist clonidine suppressed seizure development, and the antagonist idazoxan enhanced the onset of seizures, suggesting that endogenous norepinephrine provides anticonvulsant properties. Administration of the norepinephrine depleter DSP-4 potentiated pilocarpine-induced seizures. These results suggest that the previously reported impairment of noradrenergic function by lithium may play a role in its potentiation of cholinomimetic-induced seizures.

Reduction of Na+ enhances phosphoinositide hydrolysis and differentiates the stimulatory and inhibitory responses to quisqualate in rat brain slices

The concentration of Na+ in the incubation medium significantly influenced phosphoinositide hydrolysis induced by some, but not all, agonists in rat cerebral cortical slices. Reductions of the Na+ concentration below 120 mM resulted in incremental increases in basal and norepinephrine-stimulated accumulation of [3H]inositol monophosphate in cortical slices that had been prelabelled with [3H]inositol, and maximal responses were obtained with 0 and 5 mM Na+. In contrast, the responses to carbachol and ibotenate were similar in medium containing 120 or 5 mM Na+. In medium with 120 mM Na+, quisqualate has two effects on phosphoinositide hydrolysis in cortical slices, including a relatively weak stimulatory effect and an inhibitory modulation of the stimulation induced by norepinephrine. These two responses to quisqualate were differentially modulated by Na+; in 5 mM compared with 120 mM Na+ the stimulatory response was greatly increased and the inhibitory effect was mostly eliminated. That these were two separate events was confirmed by the use of L-BOAA (beta-N-oxalyl-L-alpha, beta-diaminopropionic acid), which reproduces the inhibitory, but not the stimulatory effect of quisqualate on phosphoinositide hydrolysis. In 5 mM Na+, inhibition by L-BOAA of norepinephrine-stimulated phosphoinositide hydrolysis was completely eliminated. These results demonstrate that a physiological concentration of Na+ maintains phosphoinositide hydrolysis at a submaximal level of sensitivity to some, but not all, agonists. The differential effects of Na+ on the stimulatory and inhibitory effects of quisqualate further substantiate the suggestion that these are two separate processes and indicate that alterations of the Na+ concentration may influence the effects of quisqualate, and other agonists, on phosphoinositide hydrolysis.

Evidence for allosteric transitions in secondary structure induced by superhelical stress

Previous studies suggest that the global secondary structures of native supercoiled and equilibrium linear DNAs may differ somewhat. Recent evidence also indicates that metastable secondary structure commonly persists following complete relaxation of the superhelical stress by intercalating dyes or by the action of topoisomerase I. In this work, the torsion constants (alpha) of pBR322, pUC8 and M13mp7 (replicative form) DNAs are determined by time-resolved fluorescence polarization anisotropy at various times subsequent to linearization. In all three cases, the torsion constants are relatively low immediately after linearization, and evolve for eight to ten weeks before reaching their apparent equilibrium values. It is shown in detail how the persistence of metastable secondary structure, subsequent to relaxation of superhelical stress, necessarily implies that one or more transitions in equilibrium secondary structure are induced as the superhelix density is varied from zero to native, or vice versa. Samples of pUC8 dimer (5434 base-pairs) with different superhelix densities are prepared by the action of topoisomerase I in the presence of various amounts of ethidium. Their median linking number differences are determined by standard band counting methods. The translational diffusion coefficient (Do) and the plateau diffusion coefficient (Dplat) characterizing internal motions over short distances (225 A) are determined by dynamic light-scattering. The torsion constant (alpha) between base-pairs and the circular dichroism spectrum are also measured for each sample. Curves of Dplat, Do, alpha and molar ellipticity ([theta]) (at the minimum near 250 nm) versus superhelix density (sigma) are constructed. The curve of Do versus sigma is very similar to that for sedimentation coefficient versus sigma for simian virus 40 (SV40) and polyoma DNAs. The curves of Dplat, Do, alpha and [theta] versus sigma show that, with increasing negative superhelix density, a structural transition occurs near sigma = -0.020 to an intermediate state with low torsion constant, and a second structural transition occurs near sigma = -0.035 to a state that exhibits more normal properties by sigma = -0.048. These data are consistent with the hypothesis that supercoiling induces two successive allosteric transitions to alternative global secondary structures. The data are much less consistent with the hypothesis that supercoiling induces some radical secondary structure at one or a few sites of small extent at sigma = -0.020, and at other sites at sigma = -0.035, or with hypotheses based on changes in tertiary structure alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of phosphoinositide metabolism in rat brain slices by excitatory amino acids, arachidonic acid, and GABA

In rat brain slices the synthesis of [3H]phosphoinositides and the production of [3H]inositol monophosphate (IP1) induced by norepinephrine (NE) were inhibited by glutamate. Calcium concentrations were varied to test if these inhibitory effects of glutamate were mediated by a calcium-dependent process. Although reducing calcium or addition of the calcium antagonist verpamil reduced the inhibitory effects of glutamate, these results were equivocal because reduced calcium directly decreased agonist-induced [3H]phosphoinositide synthesis. The inhibitory effects of glutamate were mimicked by quisqualate in a dose-dependent manner, but none of a variety of excitatory amino acid receptor antagonists modified the inhibition caused by quisqualate. It is suggested that glutamate activates a quisqualate-sensitive receptor (for which an antagonist is not available) and causes inhibition of phosphoinositide hydrolysis mediated in part by a direct or indirect inhibitory effect of calcium on phosphoinositide synthesis. Modulatory effects of arachidonic acid were examined because glutamate and calcium can activate phospholipase A2. Arachidonic acid caused a rapid and dose-dependent inhibition of [3H]phosphoinositide synthesis and of NE-stimulated [3H]IP1 production. A similar inhibition of the response to carbachol also occurred. The inhibition caused by arachidonic acid was unchanged by addition of inhibitors of cyclooxygenase or lipoxygenase. Activation of phospholipase A2 with melittin caused inhibitory effects similar to those of arachidonic acid. Inhibitors of phospholipase A2 were found to impair phosphoinositide metabolism, likely due to their lack of specificity for phospholipase A2. Further studies were carried out in slices that were prelabelled with [3H]inositol in an attempt to separate modulatory effects on [3H]phosphoinositide synthesis and agonist-stimulated [3H]IP1 production. Several excitatory amino acid agonists inhibited NE-stimulated [3H]IP1 production. This inhibitory interaction could be due to impaired synthesis of [3H]phosphoinositides because, even though the slices were prelabeled, addition of unlabelled inositol reduced NE-stimulated [3H]IP1 production, indicating that continuous regeneration of [3H]phosphoinositides is required. In contrast to the inhibitory effects of the excitatory amino acids, gamma-aminobutyric acid (GABA) enhanced the response to NE in cortical and hippocampal slices. GABA also enhanced the response to carbachol in hippocampal and striatal slices and to ibotenic acid in hippocampal slices. Baclofen potentiated the response to NE similarly to the effect of GABA and baclofen partially blocked the inhibitory effect of arachidonic acid but did not alter that of quisqualate.

Intramolecular interference effects in dynamic light scattering: rigid double spirals and superhelical DNAs

A theory is developed for dynamic light scattering (DLS) from rigid double spirals by treating an invisible rigid cylinder with two helical scattering stripes on opposite sides of its cylindrical surface. The exact initial, or first cumulant, diffusion coefficient Dapp (K) is obtained in terms of the translational diffusion coefficients (D parallel and D perpendicular) parallel and perpendicular to the symmetry axis, the rotational diffusion coefficients (DR parallel and DR perpendicular) around the symmetry and transverse axes, the length (L) and radius (b) of the cylindrical surface bearing the stripes, and the pitch (p). Interference effects, namely geometrical antiresonances, between strands, produce deep minima in the static structure factor S (K) and corresponding prominent peaks in Dapp (K). These peaks in Dapp (K) depend sensitively on the rotational dynamics around the symmetry axis, and nearly vanish when DR parallel = 0. Some results for single spirals are also presented. A simpler model in which scattering points are attached at opposite ends of an otherwise invisible thin rigid rod is also treated, and shown to exhibit modest minima in S (K) and corresponding maxima in Dapp (K). Confining this rod to a plane containing K enhances the amplitudes of the oscillations in S (K) and Dapp (K), as expected. Rigid double spirals are employed as crude models for interwound supercoiled DNAs in order to assess the possible occurrence of interference effects. Although native supercoiled DNAs exhibit a cylinder diameter that is much too small to exhibit geometrical antiresonances in the presently accessible range of K2, nearly relaxed supercoiled DNAs are predicted to exhibit their first maximum in Dapp (K) just inside this range. Previously reported data for the effect of Escherichia coli single-strand binding (ssb) protein on the DLS of supercoiled pBR322 DNA cannot be mimicked by a gradual homogeneous reduction of superhelix density with increasing ssb, but instead can be mimicked by inhomogeneous all-or-none binding in which uncomplexed native DNAs and nearly relaxed saturated ssb/DNA complexes coexist in varying proportions. Experimental Dapp (K) and S (K) data for a sample of relaxed pUC8 dimers display, respectively, a broad maximum and a corresponding minimum, in qualitative agreement with rough theoretical predictions.

Dynamic bending rigidity of DNA

Rapidly relaxing components in the decay of the transient electric dichroism of DNA restriction fragments were reported by Diekmann et al. [(1982) Biophys. Chem. 15, 263-270] and Pörschke et al. [(1987) Biopolymers 26, 1971-1974]. These are analyzed using a new normal mode theory for weakly bending rods and assigned to bending. The longest bending relaxation times for fragments with 95-250 base pairs coincide with the theoretical curve calculated for a dynamic bending rigidity corresponding to a dynamic persistence length Pd = 2100 A. Analysis of the relative amplitudes of fast and slow components following weak orienting pulses is also consistent with a rather large dynamic persistence length. The enhancement of the relative amplitude of the fast component in large electric fields is attributed to steady-state bending of initially perpendicular DNAs by the field. Several reasons are proposed why the dynamic bending rigidity is 4 times larger than the apparent static bending rigidity inferred from equilibrium persistence length measurements on the same fragments.

Influence of the substrate temperature on the holographic properties of Se and SeGe thin films

The effects of the substrate temperature (T(s)) on the optical constants of as-deposited Se and SeGe thin films and on the holographic recording properties of these films were investigated. The substrate temperature held between 35 degrees C and 50 degrees C during thin film deposition was identified as an appropriate means to improve the optical recording properties of these films.

[Scanning electron microscopy observations on the vascular casts of the placental chorion in normal pregnancy and pregnancy-induced hypertension]

The method of vascular casting in human placental chorion for scanning electron microscopy (SEM) was described. Through SEM of the placental chorion in five normal pregnant cases and twenty-two pregnancy induce hypertension (PIH), the three-dimensional angioarchitecture of the placental chorion in normal pregnancy and PIH of different clinical classes were clarified. Increasing with the severity of PIH, the capillaries in the placental chorion became more and more attenuated and irregular in diameter, with their branches decreasing in number and the inner wall roughened. These capillary changes were found even in mild PIH. However, the pathological changes in the chorionic capillaries in moderate and severe cases treated beforehand with magnesium sulfate were much less than those in untreated cases.

Interaction of chloroquine with linear and supercoiled DNAs. Effect on the torsional dynamics, rigidity, and twist energy parameter

The magnitude and uniformity of the torsion elastic constant (alpha) of linear pBR322 DNA and supercoiled pBR322 DNAs with high-twist (sigma = -0.083) and normal-twist (sigma = -0.48) are measured in 0.1 M NaCl as a function of added chloroquine/base-pair ratio (chl/bp) by studying the fluorescence polarization anisotrophy (FPA) of intercalated ethidium dye. The time-resolved FPA is measured by using a picosecond dye laser for excitation and time-correlated single-photon counting detection. A general theory is developed for the binding of ligands that unwind superhelical DNAs, and the simultaneous binding of two different intercalators is treated in detail. The equilibrium constant (K) for binding chloroquine to linear pBR322 DNA and the number (r) of bound chloroquines per base pair are determined from the relative amplitude ratio of the slow (normally intercalated) and fast (free) components in the decay of the (probe) ethidium fluorescence intensity as a function of chl/bp. For chloroquine binding to supercoiled pBR322 DNAs, the intrinsic binding constant is assumed to be the same as for the linear DNA, but the twist energy parameter ET (N times the free energy to change the linking number from 0 to 1 in units of kBT) is regarded as adjustable. Using the best-fit ET, the binding ratios r are calculated for each chl/bp ratio. Twist energy parameters are also determined for ethidium binding to these supercoiled DNAs by competitive dialysis. For chloroquine binding, we obtain ET = 360 and 460 respectively for the normal-twist and high-twist supercoiled DNAs. For ethidium binding the corresponding values are ET = 280 +/- 70 and 347 +/- 50. Like other dye-binding values, these are substantially lower than those obtained by ligation methods. In the absence of chloroquine, the torsion constants of all three DNAs are virtually identical, alpha = (5.0 +/- 0.4) x 10(-12) dyn.cm. For linear pBR322 DNA, the magnitude and uniformity of alpha remain unaltered by intercalated chloroquine up to r = 0.19. This finding argues that the FPA is not significantly relaxed by diffusion of any kinks or solitons. If alpha d denotes the torsion constant between a dye and a base pair and alpha 0 that between two base pairs, then our data imply that alpha d/alpha 0 lies in the range 0.65-1.64, with a most probable value of 1.0.(ABSTRACT TRUNCATED AT 400 WORDS)

Real-time hologram recording in SeGe films

Hologram characteristics of Se(1-x)Ge(x) (x = 0, 3,5,8, 12 wt.%) films were determined in real-time configuration. Parameters such as film thickness, composition, and exposure power influencing the diffraction efficiency were also studied. The maximum value of the diffraction efficiency achieved was 3.2% with 91.0-mW/cm(2) power in films alloyed with 3% Ge. Microstructural changes before and after the exposure were determined using transmission electron microscopy.