Isocupressic acid blocks progesterone production from bovine luteal cells

The needles of ponderosa pine (Pinus ponderosa Laws.) were reported to induce abortions when fed to late-term pregnant beef cows in North America. An in vivo study of pregnant cows suggested that isocupressic acid (IA) was the main abortifacient isolated from needles and bark of the pine. However, the mechanism of abortifacient activity of IA is not clear yet. In a pregnant cow, the corpus luteum of the ovary helps the maintenance of pregnancy by its progesterone production. This study involved the IA extracted from the root of the Taiwan cypress (Juniperus formosana) and used a frozen-thawed bovine luteal cell culture system to investigate the action of IA on progesterone production. Thawed bovine luteal cells (1 x 10(5) cells/ml/well) in M199 medium were cultured in 24-well culture plates at 37 degrees C in a 5% CO2 incubator. Ten ml of tested drugs, IA at 1 to 1000 ng/ml and/or ovine luteinizing hormone (oLH) at 1 to 100 ng/microl or 8-bromo-cyclic adenosine monophosphate (8-Br-cAMP) with 0.1-10 mM, were added into each well. After 4 hours of incubation, the media were harvested and assayed for progesterone by an enzyme immunoassay. Progesterone production from cells was the indicator used to evaluate the action of IA. All tested doses of IA significantly inhibited progesterone production in both basal and oLH stimulating conditions. Also those dosages inhibited cyclic adenosine-3',5'- monophosphate (cAMP) stimulation, suggesting a post-cAMP mechanism is involved in the IA action. We concluded that IA can induce pregnant cows to abort partly through blocking luteal function and may be identified as a new abortifacient chemical.

Dynamic scaling theory for a tethered membrane in solution

We present the dynamic scaling behavior for the specific viscosity and diffusion coefficient of a single membrane and membranes with nonzero concentration in solution. Starting from the membrane free energies, we derive their Langevin equations. The corresponding Kirkwood diffusion equation, describing the time evolution in configuration space, contains two kinds of time scales that are separated by the external dimension 4/(2-D) where D is the dimension of the internal space. These time scale separation behaviors depend strongly on the hydrodynamic screening effect. For a single membrane solution, we resolve the dynamic scaling exponents for the diffusion coefficient and intrinsic viscosity by the dimension reduction method. For a concentrated membrane solution, the effective excluded volume strength and draining parameter are introduced. The effective medium argument is applied to obtain a concentration dependent power law form for the specific viscosity and diffusion coefficient, whose results contribute to a fundamental understanding of membrane in solution and of hydrodynamic screening and excluded volume effects in many different solvents.

Ginseng flowers stimulate progesterone production from bovine luteal cells

Our previous report first showed evidence that polysaccharides isolated from ginseng leaves obtained from Jilin, China possess luteotropic activities. In this study, we made further investigations on the root and flowers of Korean ginseng by means of the same bioassay system described briefly as follows. Frozen-thawed bovine luteal cells (1 x 10(5) cells/ml/well) in M199 were incubated in 24-well culture plates at 37 degrees C in a 5 % CO2 incubator. Ten microl of tested drugs with 1, 10 and 100 microg/ml were added into each well. After 4- and 24-hr incubation, the media were harvested and assayed for progesterone by an enzyme immunoassay. The production of progesterone from cells is the indicator for evaluating the action of tested drugs. Results showed that hot water extracts ofginseng flowers (GF-1) with 10 to 100 microg/ml significantly increased progesterone production, whereas those from ginseng root (GR-1) could not. Crude polysaccharides (GF-2) isolated from GF-1 is the active component and the small molecules (mw < 10,000 dalton) are excluded, indicating that the ginseng root has no luteotropic activities, but the polysaccharides of ginseng flowers have.

Simulation of the wiener sausage

The volume of a region visited by a spherical Brownian particle for a time t, known as the Wiener sausage, is an important random variable characterizing Brownian motion. A Brownian dynamics simulation is used to study statistical properties of the Wiener sausage volume. We show that the probability density is closely approximated by a Gaussian distribution not only at asymptotically long times, but over a wide range of times as well. We also refine the expression for the dispersion by finding a correction term for the long-time asymptotic dependence.

Dynamical principles in biological processes: a model of charge migration in proteins and DNA

The generalized master equations (GMEs) that contain multiple time scales have been derived quantum mechanically. The GME method has then been applied to a model of charge migration in proteins that invokes the hole hopping between local amino acid sites driven by the torsional motions of the floppy backbones. This model is then applied to analyze the experimental results for sequence-dependent long-range hole transport in DNA reported by Meggers et al. [Meggers, E., Michel-Beyerle, M. E., & Giese, B. (1998) J. Am. Chem. Soc. 120, 12950-12955]. The model has also been applied to analyze the experimental results of femtosecond dynamics of DNA-mediated electron transfer reported by Zewail and co-workers [Wan, C., Fiebig, T., Kelley, S. O., Treadway, C. R., Barton, J. K. & Zewail, A. H. (1999) Proc. Natl. Acad. Sci. USA 96, 6014-6019]. The initial events in the dynamics of protein folding have begun to attract attention. The GME obtained in this paper will be applicable to this problem.

Trapping by clusters of traps

We study how the trapping kinetics is modified when traps are gathered in clusters. Recently, we have proposed a mean-field theory of trapping by clusters of traps valid at the initial stage of the process [J. Chem. Phys. 111, 711 (1999)]. Here by using the optimal-fluctuation method we incorporate fluctuation effects in the theory and discuss the manifestation of trap clustering in the kinetics over the entire time domain. Notable observations are that due to trap clustering (1) the trapping kinetics can be significantly modified from the very beginning of the process; (2) the fluctuation-induced kinetics exhibits more rich behavior; (3) the fraction of particles reacting according to a stretched-exponential law can be substantially increased.

Charge conductivity in peptides: dynamic simulations of a bifunctional model supporting experimental data

Our previous finding and the given mechanism of charge and electron transfer in polypeptides are here integrated in a bifunctional model involving electronic charge transfer coupled to special internal rotations. Present molecular dynamics simulations that describe these motions in the chain result in the mean first passage times for the hopping process of an individual step. This "rest and fire" mechanism is formulated in detail-i.e., individual amino acids are weakly coupled and must first undergo alignment to reach the special strong coupling. This bifunctional model contains the essential features demanded by our prior experiments. The molecular dynamics results yield a mean first passage time distribution peaked at about 140 fs, in close agreement with our direct femtosecond measurements. In logic gate language this is a strongly conducting ON state resulting from small firing energies, the system otherwise being a quiescent OFF state. The observed time scale of about 200 fs provides confirmation of our simulations of transport, a model of extreme transduction efficiency. It explains the high efficiency of charge transport observed in polypeptides. We contend that the moderate speed of weak coupling is required in our model by the bifunctionality of peptides. This bifunctional mechanism agrees with our data and contains valuable features for a general model of long-range conductivity, final reactivity, and binding at a long distance.

Involvement of protein kinase C-gamma in IL-1beta-induced cyclooxygenase-2 expression in human pulmonary epithelial cells

The signaling pathway of protein kinase C (PKC) is known to play a role in mediating the action of various cytokines. Here we examined the signal transduction pathway of PKC activation and the role of PKC isoforms in interleukin-1beta (IL-1beta)-mediated cyclooxygenase-2 (COX-2) expression in human pulmonary epithelial cell line (A549). The tyrosine kinase inhibitors (genistein and tyrphostin AG126) and phosphatidylcholine-phospholipase C inhibitor (D-609) prevented IL-1beta-induced prostaglandin E(2) (PGE(2)) release and COX-2 expression, whereas U-73122 (a phosphatidylinositol-phospholipase C inhibitor) and propranolol (a phosphatidate phosphohydrolase inhibitor) had no effect. The PKC inhibitors (Go 6976 and Ro 31-8220) and NF-kappaB inhibitor, pyrrolidine dithiocarbamate, also attenuated IL-1beta-induced PGE(2) release and COX-2 expression. Western blot analysis using PKC isoenzyme-specific antibodies indicated that A549 cells expressed PKC-alpha, -gamma, -iota, -lambda, -zeta, and -micro. IL-1beta caused the translocation of PKC-gamma but not other isoforms from cytosol to the membrane fraction. Moreover, the translocation of PKC-gamma was inhibited by genistein or D-609, but not by U-73122. IL-1beta caused the translocation of p65 NF-kappaB from cytosol to the nucleus as well as the degradation of IkappaB-alpha in cytosol. Furthermore, the translocation of p65 NF-kappaB was inhibited by genistein, Go 6976, Ro 31-8220, or pyrrolidine dithiocarbamate. These results indicate that in human pulmonary epithelial cells, IL-1beta might activate phosphatidylcholine-phospholipase C through an upstream tyrosine phosphorylation to elicit PKC activation, which in turn initiates NF-kappaB activation, and finally induces COX-2 expression and PGE(2) release. Of the PKC isoforms present in A549 cells, only activation of PKC-gamma is involved in regulating IL-1beta-induced responses.

Scavenging effect of benzophenones on the oxidative stress of skeletal muscle cells

Benzophenone is an ultraviolet (UV)-absorbing agent that has been used in industry and medicine for more than 30 years. Consumers of cosmetics and sunscreens containing UV-absorbers are exposed to benzophenones on a daily basis, owing to the widespread use of these compounds. However, the efficacy of these compounds as scavengers of oxidative stress is still not well established. In the present study, we investigate the antioxidative capacity of six sunscreen benzophenone compounds. A primary myoblast culture was mixed in vitro with 100 microM menadione. The cytotoxic effect by menadione-induced oxidative stress was monitored by the lucigenin- or luminol-amplified chemiluminescence, methylthiotetrazole (MTT) assay, and the antioxidative effects of various benzophenone compounds were evaluated. The results showed that the addition of menadione can induce oxidative stress on myoblasts by superoxide and hydrogen peroxide production, which can be eradicated by superoxide dismutase (SOD) and catalase, respectively, in a dose-dependent mode. The catalase has a protective effect on the cytotoxicity induced by menadione as measured by the MTT assay, while the SOD does not. The selected benzophenones also have a significant scavenging effect on the menadione-induced cell death on the myoblasts. The ortho-dihydroxyl structure and other hydroxy groups in the same ring have a stronger scavenging effect on the superoxide anion on myoblasts; thus, a stable penoxy radical may be formed. The mechanism of this effect remains to be clarified.

Benzophenones as xanthine oxidase inhibitors

Eight synthetic benzophenones were tested for their inhibitory effects on xanthine oxidase (XO). The enzyme, XO catalyses the oxidation of hypoxanthine to xanthine and of xanthine to uric acid, which has a lambda max of 295 nm, forming the basis for a spectrophotometric assay for the activity of XO. The results showed that 2,2',4,4'-tetrahydroxybenzophenone (6), 3,4,5,2',3',4'-hexahydroxybenzophenone (8) and 4,4'-dihydroxybenzophenone (3) displayed the inhibitory effects on XO with an order of activity of IC50 = 47.59, 69.40 and 82.94 microM, respectively. The apparent inhibition constants (Ki) of (8) and (3) were 15.61 and 64.86 microM respectively, and both of them induced mixed type (non-competitive-uncompetitive) inhibitions of the substrate xanthine.

Expression of foreign antigens on the surface of Escherichia coli by fusion to the outer membrane protein traT

The traT gene is one of the F factor transfer genes and encodes an outer membrane protein which is involved in interactions between an Escherichia coli and its surroundings. This protein was altered so as to permit the expression of foreign proteins on the outer membrane of E. coli in this study. A 729-bp DNA fragment, including the leader and entire structural gene sequence of traT, was amplified and obtained by PCR. This sequence was then subcloned downstream of the tac promoter of pDR540, resulting in a TraT expression vector, pT2. Here, we report that the expression of TraT protein, fused either with a partial pre-S antigen of hepatitis B virus (60 and 98 amino acids, respectively) or with the snake venom rhodostomin (72 amino acids), was successfully achieved on the outer membrane of E. coli, using the pT2 plasmid. This result was demonstrated using dot blot and immunofluorescence analysis. This finding supports the notion that the pT2 plasmid can be used as an E. coli display system. This system can detect a foreign peptide of about 100 amino acid residues in length on the bacterial surface.

Inhibition of xanthine oxidase by benzothiazinone analogues

Fourteen synthetic benzothiazinone analogues were tested for their inhibitory effects on xanthine oxidase. The enzyme, xanthine oxidase (XO) catalyses the oxidation of hypoxanthine to xanthine and of xanthine to uric acid, which has a lambda max of 295 nm, forming the basis for a spectrophotometric assay for the activity of xanthine oxidase. The results showed that 2-amino-4H-1,3-benzothiazine-4-one (1), 2-guanidino-4H-1,3-benzothiazin-4-one (2) and rhodanine (3) display inhibitory effects on xanthine oxidase with an order of activity of IC50 = 5.54, 5.60 and 121.40 microM respectively. The apparent inhibition constants (Ki) were 5.12, 19.47 and 206.23 microM, and induced non-competitive, mixed type (non-competitive-uncompetitive) and mixed type (non-competitive-uncompetitive) inhibitions respectively with respect to the substrate xanthine.

Inhibition of xanthine oxidase by purpurogallin and silymarin group

Thirteen phenolic compounds were tested for their inhibitory effects on xanthine oxidase. The enzyme xanthine oxidase catalyses the oxidation of hypoxanthine to xanthine and of xanthine to uric acid, which has lambda max of 295 nm, forming the basis for a spectrophotometric assay of the activity of xanthine oxidase. The results showed that purpurogallin and silymarin group displayed the inhibitory effects on xanthine oxidase (IC50 = 2.96 +/- 0.12 and 27.58 +/- 3.48 microM, respectively). Their apparent inhibition constants (Ki) were 1.16 and 5.85 microM, and induced uncompetitive and mixed type (non-competitive-uncompetitive) inhibitions respectively, with respect to the substrate xanthine.

Superoxide anion scavenge effect of Quercus glauca Thunb. in whole blood of patients with ankylosing spondylitis

Nine phenolic compounds, catechin (1), epicatechin (2), gallocatechin (3), epigallocatechin (4), procyanidin B-4 (5), catechin-3-O-rhamnoside (6), rutin (7), querglanin (8) and isoquerglanin (9) were isolated from oak leaves (Quercus glauca Thunb. Fagaceae), and the latter two (8, 9) were identified as new compounds. Several Quercus species have been used in folk medicine as an astringent for hemorrhoids and for treatment of inflammation, jaundice, and tumor. In this study, these compounds were tested for scavenging effects of the superoxide anion in the whole blood of patients with ankylosing spondylitis by means of an ultra-sensitive chemoluminescence (CL) analyzer and lucigenin amplification. The results showed that at a concentration of 2.3 x 10(-5) M, isoquerglanin (9) displayed the strongest inhibition activity (73.55%), followed by querglanin (8) (68.81%) and then gallocatechin (3) and epigallocatechin (4) (66.97 and 60.17% inhibition, respectively). In addition, the blood chemoluminescence (CL) level of patients with ankylosing spondylitis was inhibited by superoxide dismutase (SOD) but not by catalase, suggesting that superoxide anion is the major component of reactive oxygen species (ROS) involved in this assay system.

Inhibition of xanthine oxidase by hydroxylated anthraquinones and related compounds

Eighteen anthraquinones and related compounds were tested for their inhibitory effects on xanthine oxidase. The enzyme, xanthine oxidase catalyses the oxidation of hypoxanthine to xanthine and of xanthine to uric acid, which has a lambda max of 295nm, forming the basis for a spectrophotometric assay of the activity of xanthine oxidase. The results showed that anthrarobin and purpurin showed moderate effects on xanthine oxidase inhibition (IC50 = 68.35 and 105.13 microM; Ki = 122.38 and 130.49 microM respectively), and both of them induced mixed type (competitive-non-competitive) inhibition with respect to the substrate xanthine.

Inhibition of xanthine oxidase by synthetic cytokinin analogues

Thirteen synthetic cytokinin analogues were tested for their inhibitory effects on xanthine oxidase. The enzyme, xanthine oxidase catalyses the oxidation of hypoxanthine to xanthine and of xanthine to uric acid, which has a gamma max of 295 nm, forming the basis for a spectrophotometric assay of the activity of xanthine oxidase. The results showed that 8-azaadenine(1), 4-amino-6-hydroxypyrazolo [3,4-d] pyrimidine(4), 4-amino-6-mercaptopyrazolo [3,4-d] pyrimidine(5) and 4-aminopyrazolo [3,4-d] pyrimidine(6) display inhibitory effects on xanthine oxidase with an order of activity of IC50 = 0.54, 5.91, 8.17 and 25.46 microM, respectively. Their apparent inhibition constants (Ki) were 0.66, 1.54, 6.61 and 26.79 microM, and induced mixed(competitive-non-competitive), competitive, mixed (competitive-non-competitive), and competitive types of inhibition respectively, with respect to the substrate xanthine.

Inhibition of xanthine oxidase by cytokinins and related substances

Fourteen cytokinins were tested for their inhibitory effects on xanthine oxidase. The enzyme, xanthine oxidase catalyses the oxidation of hypoxanthine to xanthine and of xanthine to uric acid which has lambda max of 295 nm, forming the basis for a spectrophotometric assay of the activity of xanthine oxidase. The results showed that adenine-HCl, N6-(2-isopentenyl)-adenine, purine and DL-dihydrozeatin displayed very potent activities (IC50 = 1.92, 10.99, 60.98 and 86.36 microM respectively). Their apparent inhibition constants (Ki) were 2.20, 17.99, 13.59 and 115.62 microM, and induced competitive, uncompetitive, competitive and non-competitive type inhibitions respectively with respect to the substrate xanthine.

Site-directed mutations of the catalytic and conserved amino acids of the neuraminidase gene, nanH, of Clostridium perfringens ATCC 10543

The small nanH gene encoding the neuraminidase from Clostridium perfringens ATCC 10543 was cloned in JM109 using pUC19 as a vector. Sequence analysis revealed an ORF encoding 382 amino acids without a signal peptide sequence. Four regions of amino-acid sequence, 71-82, 140-151, 208-219, and 255-266 constituted four repeated and conserved sequence motifs-Ser-X-Asp-X-Gly-X-Thr-Trp-, the "Asp boxes." When compared, the nanH polypeptides of C. perfringens ATCC 10543 and Salmonella typhimurium LT12 shared 33% sequence identity and 60% similarity if conservative replacements were included. The homology-modeled structure of C. perfringens NanH showed the same folding topology as the x-ray three-dimensional structure of NanH in S. typhimurium LT12. Amino acid residues Arg37, Arg56, Asp62, His63, Asp100, Glu230, Asp247, Tyr347, and Glu362 located around the pocket of modeled C. perfringens small nanH were superimposed with the active-site pocket of S. typhimurium LT12, nanH. The catalytic amino-acid residues as well as the role of the "Asp boxes" have not been characterized for C. perfringens and S. typhimurium. In this study, Asp100, Glu230, and Asp62 were found to be involved in the catalytic activity of C. perfringens small nanH with immunoreactive properties and site-directed mutagenesis analysis. Four "Asp-box" motifs were found remote from the active-site pocket. Mutational and immunoreactive analysis of the highly conserved amino acids located in the "Asp boxes" suggest that these highly conserved residues are important in maintaining the tertiary structure of NanH. The results of this study provide some knowledge for the design of new inhibitors of small neuraminidase.

No intermolecular interaction between the large hepatitis delta antigens is required for the secretion with hepatitis B surface antigen: a model of empty HDV particle

The large delta antigen (LDAg) of hepatitis D virus (HDV), which is similar to the small delta antigen (SDAg), except it has 19 additional amino acids and an isoprenylation signal at the C-terminus, is crucial for interacting with hepatitis B surface antigen (HBsAg) to form a mature virion of HDV. Previous studies indicated that the LDAg alone, but not SDAg, can interact with HBsAg to form an empty particle. However, no evidence yet shows whether the intermolecular interaction of LDAg is necessary for forming an empty HDV particle. By cotransfection of plasmids encoding deletion or isoprenylation-negative mutants of LDAg with a plasmid encoding HBsAg into human hepatoma cells, we demonstrated that (i) the isoprenylation-negative LDAg cannot be secreted, (ii) the coiled-coil domain-deleted LDAg retains the secretion capability, (iii) the isoprenylation-negative LDAg can neither cosecrete with isoprenylation-positive LDAg nor suppress its secretion, and (iv) an intermolecular interaction between LDAgs is unlikely required for secretion. A hypothetical model of empty HDV particle containing HBsAg with isoprenylated LDAgs, which are probably present in a singular form, was then proposed.

Inhibitory effects of plant growth regulators on xanthine oxidase

Several plant hormones and analogues were tested for their inhibitory effects on xanthine oxidase. The flavoprotein enzyme, xanthine oxidase, catalyses the oxidation of hypoxanthine to xanthine and then xanthine to uric acid which has lambda max 295 nm. Uric acid was thus the basis for a spectrophotometric assay of the activity of xanthine oxidase. The results showed that trans-zeatin displayed the strongest activity (IC50 = 23.5 muM) on xanthine oxidase inhibition, followed by indole-3-acrylic acid (IC50 = 136.0 muM) and then by the mixed isomers of zeatin (trans-zeatin and cis-zeatin) (IC50 = 198.65 muM). Trans-zeatin induced an uncompetitive inhibition of the enzyme with respect to the substrate xanthine and the apparent inhibition constant (Ki) was 5.09 muM. However, zeatin riboside was inactive. Since xanthine oxidase serum levels are increased in hepatitis, mild hepatic intoxication, tumours brain tissues, and DNA damage induced by cytotoxic agents, it is expected that trans-zeatin may be useful for the treatment of these diseases as well as gout which is caused by deposition of uric acid in the joints and oxidative damage of tissue caused by generation of superoxide anion radical.

Deletion or alteration of hydrophobic amino acids at the first and the third transmembrane domains of hepatitis B surface antigen enhances its production in Escherichia coli

To investigate the failure of high-level production of hepatitis B viral (HBV) surface antigen (HBsAg), including three authentic forms, large (L), middle (M) and major/small (S) HBsAg, in Escherichia coli, we employed the high-expression vector pGEX containing the glutathione S-transferase-encoding gene (GST) to study HBsAg production. Different fragments of HBV DNA containing the entire pre-S1/pre-S2/S region (for L protein), or partial pre-S1, pre-S2, pre-S1/pre-S2 and pre-S2/S region (for M protein), were fused downstream from the GST gene, in order to obtain five plasmids which encode GST-HBsAg fusion proteins. SDS-PAGE analyses revealed that cells containing plasmids with a full-length S region (pGLS and pGMS) produced undetectable GST-HBsAg fusion proteins, in contrast to those cells harboring plasmids without the S region (pGS1, pGS2 and pGS1S2), which synthesized fusion proteins in 3-10% of the total cellular protein. Using an immunoblot method to screen HBsAg production in cells which harbored plasmids derived from exonuclease BAL 31-digested pGLS, we obtained eight positive clones. Nucleotide sequence analyses of plasmids from the positive clones revealed that termination, deletion or frameshift occurred at the regions encoding either the first or the third transmembrane domain of the major HBsAg. Correlation between the production level of GST-HBsAg fusion proteins and their constituent and arrangement of amino acids (aa) at the last 20 aa among 15 clones suggested that the fusion protein ended with a longer stretch of or a higher ratio of hydrophobic aa had a lower production in E. coli.

Biogenesis of the hepatitis B viral middle (M) surface protein in a human hepatoma cell line: demonstration of an alternative secretion pathway

In the serum of hepatitis B virus (HBV)-infected patients, two different types of particles, a 42 nm virion and a 22 nm subviral particle, were identified. The envelope of both particles is composed of three proteins, the large (L), middle (M), and major/small (S) surface proteins but the ratio between these components varies in each. The M protein appears in a lesser amount than the S protein in both virion and subviral particles, although it is translated from the same subgenomic RNA, and this is due to its poor initiation context of translation. In addition, only the glycosylated form of M protein is secreted in contrast to both glycosylated and unglycosylated forms of L and S proteins that are secreted. To investigate the biogenesis of M protein, human hepatoma cells transfected with plasmids containing a mutated HBV DNA were used to produce a high amount of M protein. Electron microscopic observation revealed that despite a higher proportion of the M protein being found in the transfected cells, the secreted surface antigen particles possess similar size and density to 22 nm subviral particles. Detailed biochemical analyses showed the following. (1) The unglycosylated M protein was predominantly present in the microsomal fraction but not present in any other subcellular fractions. (2) The M protein formed 22-nm-like particles in the endoplasmic reticulum (ER) and was retained in the post-ER or pre-Golgi regions. (3) In addition to the complex glycosylated form of M protein, a high-mannose form of M protein could be secreted. (4) Normally, no unglycosylated M protein was secreted. However, glycosylation was not essential for M protein secretion since M protein deprived of glycosylation by tunicamycin treatment was detected in the medium. These findings suggest that (i) the M protein was probably translated and co-translocated into the ER and at least one site was glycosylated before leaving the ER resulting in no secretion of unglycosylated M protein, and (ii) the M protein had two secretion pathways, one through the conventional pathway and the other probably directly through the ER.

Preferential ribosomal scanning is involved in the differential synthesis of the hepatitis B viral surface antigens from subgenomic transcripts

The envelope of the hepatitis B virus (HBV) is composed of three species of proteins, the large (L), middle (M), and major (S) surface proteins (HBsAgs), each of different molecular weights but sharing a common C-terminus. These three HBsAgs, encoded by two species of viral subgenomic transcripts (2.1 and 2.4 kb), which have a heterogenous 5'-terminus, appear in different amounts in both the 42-nm virions and the 22-nm subviral particles. To investigate the involvement of translational control in the differential expression of the L, M, and S proteins, we tested the translational capability of 2.1- and 2.4-kb transcripts in in vitro translation and of 2.1-kb transcripts in in vivo transfection experiments. Results of in vitro translation indicated that a large amount of the L protein and a very small amount of the M and S proteins were synthesized from the 2.4-kb mRNA. Translation of the 2.1-kb mRNA resulted in a 4:1 ratio of the S protein to the M protein. In contrast, translation of a similar 2.1-kb mRNA containing an optimal initiation context (5'-ACCATGG-3') of the pre-S2 region resulted in a reversed ratio, four times as much M protein as S protein. This result was also obtained by transfection of hepatoma cells with plasmid DNAs containing the mutated sequence (5'-ACCATGG-3') of the pre-S2 region. In considering these results, the production of a large amount of the L protein from the 2.4-kb mRNA and the determination of the level of the M protein by the context of translational initiation, we suggest that a preferential translational initiation is involved in the expression of differential amounts of the L, M, and S proteins.

Characterization of monoclonal antibody binding site to the polymorphic length of hepatitis B surface antigen synthesized in a cell-free system

A combination of two modern biological techniques, hybridoma and recombinant DNA, was described to screen and characterize a monoclonal antibody binding site. Three monoclonal antibodies, M27, M9 and M01 recognizing to a specific domain of the hepatitis B virus surface antigen (HBsAg), were determined by their ability to immunoprecipitate the in vitro synthesized HBsAg in a polymorphic length. Results indicated that the M9 and M01 both recognize the S region of surface antigen while the M27 binds to the pre-S2 region of surface antigen.

Evidence of a new metabolic pathway of 5-fluorouracil in Escherichia coli from in vivo 19F-NMR spectroscopy

Two distinct metabolic pathways of 5-fluorouracil are proposed in Escherichia coli. The first metabolic pathway is a reductive degradation with the formation of dihydrofluorouracil as the first metabolite. The second metabolic pathway is shown to be a hydroxylating degradation, possibly with the formation of 5-hydro-6-hydroxy-5-fluorouracil as the first metabolite. The metabolites of both pathways undergo subsequent hydrolytic degradation with fluoride ion as the common final product. The chemical structures of these metabolites were partially identified by 19F-NMR. The results show a close resemblance between these two metabolic pathways with in vivo pyrimidine biodegradation. The reductive degradation has been proposed by several laboratories, whereas the hydroxy degradation has not been reported before. Both the reductive and hydroxy pathways are demonstrated in this report, to be independent reactions.