Template supercoiling during ATP-dependent DNA helix tracking: studies with simian virus 40 large tumor antigen

Incubation of topologically relaxed plasmid DNA with simian virus 40 (SV40) large tumor antigen (T antigen), ATP, and eubacterial DNA topoisomerase I resulted in the formation of highly positively supercoiled DNA. Eukaryotic DNA topoisomerase I could not substitute for eubacterial DNA topoisomerase 1 in this reaction. Furthermore, the addition of eukaryotic topoisomerase I to a preincubated reaction mixture containing both T antigen and eubacterial topoisomerase I caused rapid relaxation of the positively supercoiled DNA. These results suggest that SV40 T antigen can introduce topoisomerase-relaxable supercoils into DNA in a reaction coupled to ATP hydrolysis. We interpret the observed T antigen supercoiling reaction in terms of a recently proposed twin-supercoiled-domain model that describes the mechanics of DNA helix-tracking processes. According to this model positive and negative supercoils are generated ahead of and behind the moving SV40 T antigen, respectively. The preferential relaxation of negative supercoils by eubacterial DNA topoisomerase I explains the accumulation of positive supercoils in the DNA template. The supercoiling assay using DNA conformation-specific eubacterial DNA topoisomerase I may be of general use for the detection of ATP-dependent DNA helix-tracking proteins.

Dorsal medullary inspiratory neurons: effects of superior laryngeal afferent stimulation

In decerebrate paralyzed cats ventilated with a cycle-triggered pump, we examined the responses of inspiratory (I) neurons in the region of the ventrolateral nucleus tractus solitarius (NTS) to single electrical stimuli delivered to the ipsilateral superior laryngeal nerve (SLN). Sixty-five I neurons were classified as: I(-), I(0), I(+, early), I(+, late) or I(other) on the basis of responses to lung inflation, and as I(bulbophrenic) or I(non-bulbophrenic) on the basis of evidence of an excitatory projection to the contralateral phrenic motoneuron pool. The peristimulus histograms of contralateral phrenic activity showed an early peak of excitation with average latency of 4.9 +/- 0.1 ms (mean +/- S.E.M.), followed by depression at 7.3 +/- 0.2 ms, start of recovery from depression at 22.7 +/- 1.0 ms, and recovery to control levels at 28.4 +/- 1.1 ms. The peristimulus histograms of ipsilateral I unit activity showed an initial excitation (latency 2.9 +/- 0.3 ms), followed by spiking silence (latency 6.0 +/- 0.6 ms) and recovery to control discharge frequency at 38.8 +/- 3.6 ms. This time of inhibition was significantly longer than the time of phrenic depression, suggesting that other bulbophrenic excitatory projections are able to rapidly compensate for decreased NTS output. Subgroups of I neurons, as classified by lung inflation tests, did not differ significantly with respect to these timing variables. In contrast, latencies of excitation for I(bulbophrenic) neurons were significantly less than for I(non-bulbophrenic) neurons.

Enhancement of nitrocaphane cytotoxicity by hyperthermia in vitro

HEp-2 cells were treated with hyperthermia (39-44 degrees C) and nitrocaphane (NC) at various time intervals. A 1 h exposure to 39 degrees C and 41 degrees C was non-lethal to cells, but it did potentiate the cell killing of NC (1.0 micrograms/ml). It was further shown that the sequence between heat and the drug can affect cell survival. Cell killing effect was decreased when heat was given before or after administration of drug. In contrast the simultaneous administration of these two modalities was synergistic. Maximal thermotolerance of HEp-2 cells was developed using an 8-h interval at 37 degrees C between the cell exposures to two equal thermal doses (44 degrees C, 30 min). HEp-2 cells became thermotolerant when preheated for 30 min at 44 degrees C followed by a 10-h interval at 37 degrees C. The thermotolerant cells showed resistance to subsequent heat at 44 degrees C (D0 = 2.26 h, control D0 = 0.38 h), to subsequent NC treatment, and to heat combined with NC. However, in the thermotolerant cells, cytotoxicity of NC was still enhanced by hyperthermia.

[New taxa of coptis from China]

The rhizomes of Coptis, known as Huang-Lian, are commonly used as traditional Chinese drugs. Two new species, viz., Coptis linearisepala, C. gulinensis and a new variety, viz., C. chinensis var. unguiculata are reported and the descriptions of the new species and new variety are presented in the present paper.

[The relationship between DNA content in cervical carcinoma cell and the clinicopathological features]

Nuclear DNA content was determined by flow cytometry in biopsy samples taken from cervical carcinomas of 33 patients. Aneuploid DNA content was found in 24 cases (72.7%). The relationship between DNA content of carcinoma cells and the clinicopathological features was investigated. Carcinomas with aneuploid DNA content were clinically more advanced and histologically poorly differentiated as compared with those with diploid DNA content. DNA content was found neither correlated with the patient's age nor with the growing type of the tumor; and analysis of DNA content by flow cytometry was considered helpful in evaluating tumor malignancy, efficacy of treatment and prognosis.

Injection of benzodiazepines but not GABA or muscimol into pars reticulata substantia nigra suppresses pentylenetetrazol seizures

The substantia nigra pars reticulata (SNpr), a brain area rich in GABA and benzodiazepine receptors, is thought to be involved in the regulation of seizure activity. It has been shown to be a site of anticonvulsant action of substances that affect GABA transmission. The anti-pentylenetetrazol (PTZ) activities of intranigral of muscimol, a GABAA receptor agonist; two benzodiazepines, midazolam and flurazepam; and GABA were examined. Microinjection of a wide dose range of both GABA and muscimol into the SNpr failed to show anti-PTZ seizure activity. Intranigral injections of midazolam and flurazepam showed clear, dose-dependent anti-PTZ effects. Ro15-1788, a benzodiazepine receptor antagonist, reversed the anticonvulsant effects of midazolam when both were infused intranigrally. Intranigral infusion of muscimol or flurazepam protected rats from bicuculline-induced tonic seizures. The results suggest that the anti-PTZ effects of benzodiazepines in SNpr might not be mediated through GABAA receptors. Another possibility is that nigral neurons bearing GABAA receptors functionally linked to benzodiazepine sites may not be representative of the whole population of nigral neurons inhibited by GABA agonists. This could result in different patterns of inhibition of nigral efferent activity by GABAA agonists and benzodiazepines.

Mechanisms for the stimulation of prostanoid synthesis by cyclosporine and bacterial lipopolysaccharide

Both cyclosporine and bacterial lipopolysaccharide enhance prostanoid synthesis and regulate the immune response. This study was designed to establish whether these agents affect prostanoid synthesis by common or different mechanisms. CsA and LPS stimulate prostanoid synthesis both in human monocytes and smooth muscle cells from guinea pig aorta. Only LPS stimulates synthesis in the presence of exogenous arachidonic acid. Dexamethasone totally blocks CsA but only partially inhibits LPS. CsA and LPS both enhance the release of labeled metabolites from cells labeled with arachidonic acid, but indomethacin only blocks the effect of LPS. CsA and the releasing agent calcium ionophore (A23187) both increase PGE2 and PGI2 synthesis without changing their relative concentrations, cause the release of free arachidonic acid, and lead to the formation of new metabolites that are not products of cyclooxygenase activity. Preincubation with either CsA or A23187 and a subsequent wash deplete the arachidonic acid pool available for prostanoid synthesis. Thus, A23187 and CsA have very similar effects on arachidonic acid metabolism. In contrast, LPS increases PGE2 and PGI2 synthesis and alters their relative concentrations, diminishes the relative concentration of free arachidonic acid, and enhances the formation of new metabolites that are products of cyclooxygenase activity. These differences are explained by mechanisms in which CsA promotes prostanoid synthesis through arachidonic acid release, and LPS promotes prostanoid synthesis through increased cyclooxygenase activity.

Synthesis of 4% Glu-containing Val1 and Ile1-polypentapeptides: model protein systems for demonstrating mechanochemical coupling

The synthesis of 4% Glu-polypentapeptide (PPP) (i.e., 4 Glu residues per 100 amino acid residues) and 4% Glu-Ile1-PPP, in which Val1 is substituted by a more hydrophobic Ile residue, is carried out by copolymerizing the p-nitrophenyl-active esters of GE(OMe)GVP and GE(OMe)GIP with their parent pentamers GVGVP and GVGIP in 1:4 ratios, respectively. After removal of the methyl ester on the side chain of Glu, these polymers exhibited a remarkable pH dependence of the temperature for their inverse temperature transitions, which are followed as turbidity development at 300 nm. On gamma-irradiation crosslinking, the elastomeric bands obtained exhibited a pH-mediated contraction and relaxation. Thus, for the first time, mechanochemical coupling is demonstrated in a synthetic polypeptide system. That the basic mechanism involves the hydrophobic effect (chemical modulation of an inverse temperature transition) and not ion-ion electrostatic repulsion is also discussed.

[Study on toxicological mechanism of moniliformin]

A mycotoxin was extracted and purified from a strain of Fusarium moniliforme var. subglutinans isolated from mouldy corn seeds harvested in a serious Keshan disease region in Shaanxi Province. The purification procedure involves water extraction, ion exchange chromatography, desalination and crystallization. Its UV spectrum, IR spectrum and NMR are identical with that of the moniliformin. The toxin is highly toxic to young Beijing ducklings. The electrocardiogram (ECG) of the duckling was changed immediately after feeding with moniliformin. The cardiac muscle cells of Beijing ducklings were injured by the toxin. Toxicity may be alleviated to certain extent by applying adequate dosage of Selenium (3.18 X 10(-10) mol/L of H2SeO4) prior to moniliformin treatment. The permeability of the cardic muscle cells of the rats and young ducklings was damaged posterior to the injection of the toxin as tested by extracellular marcromolecular tracer (HRP) method. The relationship between moniliformin and Keshan disease was discussed. We consider that the moniliformin may be the causal agent of the disease.

[Quantitative determination of 5 alkaloids in plants of Coptis from China]

Quantitative determination of berberine, coptisine, palmatine, jatrorrhizine and epiberberine in Coptis chinensis, C. deltoidea, C. teetoides, C. omeiensis, C. chinensis var. brevisepala, C. linearisepala, C. gulinensis, C. chinensis var. unguiculata, C. teeta and 5 different samples of C. chinensis was made by thin layer chromatography-densitometry.

Role of beta-receptor in the radix Angelicae sinensis attenuated hypoxic pulmonary hypertension in rats

Acute pulmonary hypertension was caused by inhalation of 5% O2 in rats. Pulmonary vascular resistance (PVR) increased, but heart rate (HR), cardiac output (CO) and carotid arterial pressure (CAP) were not obviously changed. After an intravenous administration of Radix Angelicae sinensis, the acute pulmonary hypertension induced by inhalation of 5% O2 could be attenuated, but this effect disappeared if propranolol was given before Radix Angelicae sinensis. In chronic experiments, the same results were obtained, but the protective effect of Radix Angelicae sinensis on heart function was not influenced by propranolol. It is suggested that Radix Angelicae sinensis might play a role by stimulating the beta 2-receptor in the prevention of acute and chronic hypoxic pulmonary hypertension. However, prevention of hypertrophy of the right ventricle and enhancement of heart function in chronic hypoxic rats might not be attributed to the beta 1-receptor in the heart.

Human DNA topoisomerase I is encoded by a single-copy gene that maps to chromosome region 20q12-13.2

cDNA clones of the human TOP1 gene encoding DNA topoisomerase I (EC 5.99.1.2) have been obtained by immunochemical screening of phage lambda libraries expressing human cDNA segments, using rabbit antibodies raised against purified HeLa DNA topoisomerase I. Hybridization patterns between the cloned cDNA sequences and human cellular DNA and cytoplasmic mRNAs indicate that human TOP1 is a single-copy gene. The chromosomal location of the gene has been mapped to the long arm of chromosome 20, in the region q12-13.2, by hybridization of a radioactively labeled TOP1 cDNA probe to human metaphase chromosomes and to a panel of rodent-human somatic hybrids retaining overlapping subsets of human chromosomes.

The primary structure of chicken liver cytochrome b5 deduced from the DNA sequence of a cDNA clone

A cDNA clone encoding the chicken liver cytochrome b5 was isolated by probing a library with synthetic oligonucleotides based on a partial amino acid sequence of the protein. Determination of the DNA sequence indicated a 414-nucleotide open reading frame which encodes a 138-amino acid residue polypeptide. The open reading frame contains 6 amino acids at the amino terminus which were not present on any of the cytochrome b5 polypeptides for which the amino acid sequence has been determined directly, suggesting that the protein is proteolytically processed to the mature form. The results of genomic Southern analysis were consistent with the presence of two structurally different genes in the chicken genome, raising the possibility that the soluble and membrane-bound forms of the protein are the products of separate genes.

pK shift of functional group in mechanochemical coupling due to hydrophobic effect: evidence for an apolar-polar repulsion free energy in water

In the sequential polypeptide poly[4(VPGVG),(VPGEG)] and its more hydrophobic analog poly[4(IPGVG),(IPGEG)] when the material is gamma-irradiation cross-linked to form an elastomeric matrix, mechanochemical coupling occurs on changing the pH, that is, motion and mechanical work are achieved by a change in proton chemical potential. The temperature dependence of aggregation at different pH values in phosphate buffered saline demonstrates the pK to be shifted approximately one pH unit higher for the more hydrophobic sequential polypeptide. The pH dependence of contraction or relaxation for each elastomer shows a similar shift. Data are reviewed and 2D-NMR data are presented which argue that the pK shift is not due to different conformations of the polypentapeptides. Specifically it is proposed that there exist a competition between carboxylates and hydrophobic side chains for mutually incompatible water structures; this results in an apolar-polar repulsion free energy in water with the difference in free energy reflecting the difference in the lle and Val hydrophobicities.