bluuebunny/crossref_metadata_2025 huggingface dataset:
Biochemical and spectroscopic characterization of the blue-green photoreceptor in Halobacterium halobium.
Authors: Scherrer P , McGinnis K , Bogomolni R A
Published: May 2006

Spectroscopic evidence indicates the presence of a second sensory receptor sR-II in Halobacterium halobium, which causes a repellent response to blue-green light. Reactions with hydroxylamine and NaCNBH3 and reconstitution of the bleached pigment with retinal show that it is very similar to the other retinylidene pigments bacteriorhodopsin, halorhodopsin, and especially the earlier-discovered phototaxis receptor, sensory rhodopsin, renamed sR-I587. The second sensory receptor, sR-II480, has an absorbance maximum at 480 nm and undergoes a cyclic photoreaction with a half-time of approximately 200 msec. Its predominant photocycle intermediate absorbs maximally near 360 nm. The receptor can be detected spectroscopically in the presence of sR-I587 and quantitated through its transient response to 450-nm excitation. It is selectively bleached by low hydroxylamine concentrations that are insufficient to bleach sR-I587 significantly. Its photochemical and phototactic activities can be restored by addition of retinal. The mobility of the receptor, on NaDodSO4/polyacrylamide gels, was similar or identical to that of sR-I587 and slightly faster than bacteriorhodopsin, yielding an apparent molecular mass of 23-24 kDa.
Human collagen genes encoding basement membrane alpha 1 (IV) and alpha 2 (IV) chains map to the distal long arm of chromosome 13.
Authors: Griffin C A , Emanuel B S , Hansen J R , Cavenee W K , Myers J C
Published: May 2006

At least 20 genes encode the structurally related collagen chains that comprise greater than 10 homo- or heterotrimeric types. Six members of this multigene family have been assigned to five chromosomes in the human genome. The two type I genes, alpha 1 and alpha 2, are located on chromosomes 17 and 7, respectively, and the alpha 1 (II) gene is located on chromosome 12. Our recent mapping of the alpha 1 (III) and alpha 2 (V) genes to the q24.3----q31 region of chromosome 2 provided the only evidence that the collagen genes are not entirely dispersed. To further determine their organization, we and others localized the alpha 1 (IV) gene to chromosome 13 and in our experiments sublocalized the gene to band q34 by in situ hybridization. Here we show the presence of the alpha 2 type IV locus also on the distal long arm of chromosome 13 by hybridizing a human alpha 2 (IV) cDNA clone to rodent-human hybrids and to metaphase chromosomes. To our knowledge, these studies represent the only demonstration of linkage between genes encoding both polypeptide chains of the same collagen type.
Human anti-endoplasmic reticulum autoantibodies appearing in a drug-induced hepatitis are directed against a human liver cytochrome P-450 that hydroxylates the drug.
Authors: Beaune P , Dansette P M , Mansuy D , Kiffel L , Finck M , Amar C , Leroux J P , Homberg J C
Published: May 2006

"Anti-liver/kidney microsome" (anti-LKM) autoantibodies have been found in the serum of patients with cryptogenic chronic hepatitis and with immunoallergic drug-induced hepatitis, such as those induced by halothane or by tienilic acid (called anti-LKM2 in this case). So far the nature of the human microsomal macromolecules recognized by these antibodies has not been determined. Here we show, by using immunoblot techniques, that among the macromolecules present in human adult liver microsomes, one protein called cytochrome P-450-8 is specifically recognized by most sera of patients containing anti-LKM2 antibodies but not by control serum. Human fetal liver microsomes that do not contain cytochrome P-450-8 are not recognized by the anti-LKM2 antibodies. It is also shown that anti-cytochrome P-450-8 antibodies as well as human serum containing anti-LKM2 antibodies specifically inhibit the hydroxylation of tienilic acid by human liver microsomes. These results indicate that anti-LKM2 antibodies appearing in patients with hepatitis and concomitant administration of tienilic acid are directed against a cytochrome P-450 isoenzyme that catalyzes the metabolic oxidation of this drug. This suggests a possible mechanism for the appearance of anti-organelle antibodies in a drug-induced hepatitis.
Cloning and expression of T4 DNA polymerase.
Authors: Lin T C , Rush J , Spicer E K , Konigsberg W H
Published: May 2006

The structural gene coding for bacteriophage T4 DNA polymerase (gene 43) has been cloned into inducible plasmid vectors, which provide a source for obtaining large amounts of this enzyme after induction. The T4 DNA polymerase produced in this fashion was purified by an innovative three-step procedure and was fully active.
A plasmacytoma-specific factor binds the c-myc promoter region.
Authors: Kakkis E , Calame K
Published: May 2006

We used an electrophoretic mobility-shift assay to study proteins that bind to sequences in the 5' flanking region of the murine c-myc gene. By comparing the DNA-protein complexes formed with extracts from cells representing earlier stages of B-cell development with those from plasmacytomas, we identified a plasmacytoma-specific protein that binds to a region within the c-myc promoter. Five other regions of this promoter show extensive sequence-specific binding, but the binding is not clearly B-cell stage-specific. Methylation-interference and o-phenanthroline/copper-protection experiments identified a single plasmacytoma-specific protein binding site 290 base pairs 5' of the transcription start site P1. Homologues of a core sequence, d(AGAAAGGGAAAGGA), within the 25-base-pair binding site are found at three additional sites in the murine c-myc locus. The plasmacytoma-specific occurrence of this protein suggests that it may play a role in the transcriptional repression of the normal c-myc gene observed in plasmacytomas.
Cloning of cDNA encoding steroid 11 beta-hydroxylase (P450c11).
Authors: Chua S C , Szabo P , Vitek A , Grzeschik K H , John M , White P C
Published: May 2006

We have isolated bovine and human adrenal cDNA clones encoding the adrenal cytochrome P-450 specific for 11 beta-hydroxylation (P450c11). A bovine adrenal cDNA library constructed in the bacteriophage lambda vector gt10 was probed with a previously isolated cDNA clone corresponding to part of the 3' untranslated region of the 4.2-kilobase (kb) mRNA encoding P450c11. Several clones with 3.2-kb cDNA inserts were isolated. Sequence analysis showed that they overlapped the original probe by 300 base pairs (bp). Combined cDNA and RNA sequence data demonstrated a continuous open reading frame of 1509 bases. P450c11 is predicted to contain 479 amino acid residues in the mature protein in addition to a 24-residue amino-terminal mitochondrial signal sequence. A bovine clone was used to isolate a homologous clone with a 3.5-kb insert from a human adrenal cDNA library. A region of 1100 bp was 81% homologous to 769 bp of the coding sequence of the bovine cDNA except for a 400-bp segment presumed to be an unprocessed intron. Hybridization of the human cDNA to DNA from a panel of human-rodent somatic cell hybrid lines and in situ hybridization to metaphase spreads of human chromosomes localized the gene to the middle of the long arm of chromosome 8. These data should be useful in developing reagents for heterozygote detection and prenatal diagnosis of 11 beta-hydroxylase deficiency, the second most frequent cause of congenital adrenal hyperplasia.
Transcriptional control of the endogenous MYC protooncogene by antisense RNA.
Authors: Yokoyama K , Imamoto F
Published: May 2006

A plasmid carrying antisense human MYC DNA and the gene encoding Escherichia coli xanthine/guanine phosphoribosyltransferase (Ecogpt) was introduced into human promyelocytic leukemia cell line HL-60 by protoplast fusion. High-level expression of antisense MYC RNA was obtained by selecting cells resistant to progressively higher levels of mycophenolic acid over a period of greater than 6 months. The constitutive production of MYC protein in clones producing high levels of antisense MYC RNA was reduced by 70% compared to parental HL-60 cells. Inhibition of MYC expression was observed not only at the translational but also at the transcriptional level, implying that antisense RNA can regulate transcription of the MYC gene. The Pst I-Pvu II fragment (920 base pairs) of the MYC leader sequence is the primary transcriptional target of the antisense RNA. The suppression of endogenous MYC gene expression by antisense RNA decreases cell proliferation and triggers monocytic differentiation.
Glutathione disulfide-stimulated Mg2+-ATPase of human erythrocyte membranes.
Authors: Kondo T , Kawakami Y , Taniguchi N , Beutler E
Published: May 2006

Inside-out erythrocyte membranes attached to polycationic beads manifested glutathione disulfide (GSSG)-stimulated ATPase activity. A Lineweaver-Burk plot of the ATPase activity as a function of GSSG concentration was biphasic and gave apparent Km values of 0.13 mM and 2.0 mM. These kinetics are similar to those reported for the ATP-requiring GSSG-transport systems in human erythrocytes and for the GSSG-stimulated ATPase activity in the plasma membranes of rat hepatocytes. Erythrocyte membranes that were depleted of extrinsic proteins were solubilized in 0.5% Triton X-100. Affinity chromatography on S-hexylglutathione-Sepharose 6B, with elution by a linear gradient of S-hexyl-glutathione, resulted in the resolution of two peaks of enzyme activity. One enzyme, which was eluted at approximately 0.5 mM S-hexylglutathione, had a high affinity for GSSG (apparent Km of 150 microM) and for ATP (80 microM). The other enzyme, which was eluted at approximately 1 mM S-hexylglutathione, had a low affinity for GSSG (apparent Km of 2.0 mM) and ATP (140 microM). GSSG-independent Mg2+-ATPase, Ca2+-dependent Mg2+-ATPase and Na+, K+-dependent Mg2+-ATPase were undetectable in the fractions. Addition of Ca2+, ouabain, or vanadate neither activated nor inhibited the activities, further indicating that the enzymes are distinguishable from ion-pumping ATPases. The enzymes required GSSG for activation; reduced glutathione (GSH) was ineffective. The ATPase activity of the high-Km enzyme was inhibited by addition of p-chloromercuribenzoate, N-ethylmaleimide, and iodoacetamide and was activated by treatment with dithiothreitol, whereas the ATPase activity of the low-Km enzyme was not modified by these thiol reagents. The properties of the enzymes are similar to those of ATP-dependent GSSG-transport systems in human erythrocytes, suggesting that these ATPases may function in the active transport of GSSG.
Molecular cloning of complementary DNA encoding the lignin-forming peroxidase from tobacco: Molecular analysis and tissue-specific expression
Authors: Lagrimini L. Mark , Burkhart William , Moyer Mary , Rothstein Steven
Published: May 2006

Plant peroxidases play a major role in lignin formation and wound healing and are believed to be involved in auxin catabolism and defense to pathogen attack. The function of the anionic peroxidase isozymes is best understood in tobacco. These isozymes catalyze the formation of the lignin polymer and form rigid cross-links between lignin, cellulose, and extensin in the secondary plant cell wall. We report the purification of the anionic peroxidase isozymes from tobacco and their partial amino acid sequence. An oligonucleotide probe deduced from the amino acid sequence was used to screen a tobacco leaf cDNA library and a 1200-base-pair cDNA clone was isolated and sequenced in its entirety. The predicted amino acid sequence revealed a 22-amino acid signal peptide and a 302-amino acid mature protein (
M
r
, 32,311). The amino acid sequence was compared to that of the cationic peroxidases from horseradish and turnip and was found to be 52% and 46% homologous, respectively. By RNA blot analysis, the messenger for the tobacco isozyme was found to be abundant in stem tissue while expressed at very low levels in leaf and root tissue. Four distinguishable copies of the gene were found on genomic DNA blots. The gene copy number may reflect the allotetraploid nature of
Nicotiana tabacum
.
Nuclear pore complex contains a family of glycoproteins that includes p62: glycosylation through a previously unidentified cellular pathway.
Authors: Davis L I , Blobel G
Published: May 2006

Using a monoclonal antibody (mAb 414), we previously identified a protein of 62 kDa (p62) that was localized to the nuclear pore complex by immunoelectron microscopy. We also showed that p62 binds specifically to wheat germ agglutinin. Therefore, we proposed that this nuclear pore complex protein might be a member of a recently characterized family of glycoproteins that are labeled by in vitro galactosylation of rat liver nuclei and contain O-linked monosaccharidic GlcNAc residues. In support of this, we now show that incubation with N-acetylglucosaminidase reduces the molecular mass of p62 by approximately 3 kDa because of the removal of terminal GlcNAc residues. Moreover, p62 can be galactosylated in vitro by using UDP-[3H]galactose and galactosyltransferase. We also show that most of the GlcNAc residues are added within 5 min of synthesis, when p62 is soluble and cytosolic. Thus, the addition of GlcNAc is carried out in the cytoplasm and is clearly distinct from the N- and O-linked glycosylation pathways of the endoplasmic reticulum and Golgi complex. Using another mAb with a broad specificity for nuclear GlcNAc-containing proteins, we show by immunofluorescence and protein blotting of subnuclear fractions that some of these proteins are in the interior of the nucleus, and others are most likely located in the pore complex.
Production of transforming growth factor alpha in human pancreatic cancer cells: evidence for a superagonist autocrine cycle.
Authors: Smith J J , Derynck R , Korc M
Published: May 2006

Previous work showed that cultured human pancreatic cancer cells overexpress the epidermal growth factor (EGF) receptor. In the present study, we sought to determine whether some of these cell lines produce transforming growth factor alpha (TGF-alpha). Utilizing a radiolabeled TGF-alpha cDNA in hybridization experiments, we determined that ASPC-1, T3M4, PANC-1, COLO-357, and MIA PaCa-2 cell lines expressed TGF-alpha mRNA. Serum-free medium conditioned by T3M4 and ASPC-1 cells contained significant amounts of TGF-alpha protein. Although unlabeled TGF-alpha readily competed with 125I-labeled EGF for binding, each cell line exhibited lower surface binding and internalization of 125I-labeled TGF-alpha as compared to 125I-labeled EGF. Both TGF-alpha and EGF significantly enhanced the anchorage-independent growth of PANC-1, T3M4, and ASPC-1 cells. However, TGF-alpha was 10- to 100-fold more potent than EGF. These findings suggest that the concomitant overexpression of EGF receptors and production of TGF-alpha may represent an efficient mechanism for certain cancer cells to obtain a growth advantage.
Rearrangement of the p53 gene in human osteogenic sarcomas.
Authors: Masuda H , Miller C , Koeffler H P , Battifora H , Cline M J
Published: May 2006

p53 is a 53-kDa nuclear protein that is associated with malignant transformation in several tumor model systems. In a survey of 134 human carcinomas, sarcomas, leukemias, and lymphomas obtained at surgery or from peripheral blood, we found rearrangements of the p53 gene only in osteogenic sarcomas (3 of 6 osteogenic sarcomas examined). Normal tissue from one of these patients had an unrearranged gene, indicating that the genetic abnormality in the tumor was acquired. Two of the sarcomas with rearranged genes expressed levels of p53 protein that were elevated relative to other tumors. Rearranged p53 genes were also found in human osteogenic sarcoma cell lines.
Functional expression of two neuronal nicotinic acetylcholine receptors from cDNA clones identifies a gene family.
Authors: Boulter J , Connolly J , Deneris E , Goldman D , Heinemann S , Patrick J
Published: May 2006

A family of genes coding for proteins homologous to the alpha subunit of the muscle nicotinic acetylcholine receptor has been identified in the rat genome. These genes are transcribed in the central and peripheral nervous systems in areas known to contain functional nicotinic receptors. In this paper, we demonstrate that three of these genes, which we call alpha 3, alpha 4, and beta 2, encode proteins that form functional nicotinic acetylcholine receptors when expressed in Xenopus oocytes. Oocytes expressing either alpha 3 or alpha 4 protein in combination with the beta 2 protein produced a strong response to acetylcholine. Oocytes expressing only the alpha 4 protein gave a weak response to acetylcholine. These receptors are activated by acetylcholine and nicotine and are blocked by Bungarus toxin 3.1. They are not blocked by alpha-bungarotoxin, which blocks the muscle nicotinic acetylcholine receptor. Thus, the receptors formed by the alpha 3, alpha 4, and beta 2 subunits are pharmacologically similar to the ganglionic-type neuronal nicotinic acetylcholine receptor. These results indicate that the alpha 3, alpha 4, and beta 2 genes encode functional nicotinic acetylcholine receptor subunits that are expressed in the brain and peripheral nervous system.
pH-sensitive immunoliposomes mediate target-cell-specific delivery and controlled expression of a foreign gene in mouse.
Authors: Wang C Y , Huang L
Published: May 2006

A plasmid containing the Escherichia coli chloramphenicol acetyltransferase (CAT) gene under the control of a mammalian cAMP-regulated promoter was entrapped in H-2Kk antibody-coated liposomes composed of dioleoyl phosphatidylethanolamine, cholesterol, and oleic acid (pH-sensitive immunoliposomes). The entrapped or free DNA was injected intraperitoneally into immunodeficient (nude) BALB/c mice bearing ascites tumor generated by H-2Kk-positive RDM-4 lymphoma cells. About 20% of the injected immunoliposomes were taken up by the target RDM-4 cells. Uptake was much less when liposomes without antibody were used. The presence of the targeting antibody on liposomes also significantly decreased the nonspecific uptake of liposomes by the spleen. Significant CAT enzyme activity was detected in RDM-4 cells from mice treated with DNA entrapped in the pH-sensitive immunoliposomes. Furthermore, CAT expression in RDM-4 cells was under the control of cAMP, as only the cells from mice injected with 8-bromo-cAMP and 3-isobutyl-1-methylxanthine showed CAT activity. CAT activity in liver and spleen was much lower (by factors of 12 and 5, respectively) than in the RDM-4 cells, and the activities in these reticuloendothelial organs were not regulated by cAMP. CAT activity in RDM-4 cells from mice injected with DNA entrapped in pH-insensitive immunoliposomes (containing phosphatidylcholine in place of phosphatidylethanolamine) was approximately one-fourth that in RDM-4 cells from mice injected with pH-sensitive immunoliposomes, indicating the superior delivery efficiency of the pH-sensitive liposomes. These results are discussed in terms of the DNA-carrier potential of immunoliposomes in therapy of cancer and genetic diseases.
Physiological levels of normal tRNA(CAGGln) can effect partial suppression of amber mutations in the yeast Saccharomyces cerevisiae.
Authors: Weiss W A , Edelman I , Culbertson M R , Friedberg E C
Published: May 2006

A number of ciliated protozoa are known to read the stop codons UAA and UAG as sense codons that specify glutamine during protein synthesis. In considering evolutionary mechanisms for this curious divergence from the standard genetic code, we propose the existence of progenitor tRNAs for glutamine that can weakly suppress UAA and UAG codons. It has been previously shown that multicopy plasmids that overexpress normal tRNA(CAAGln) and tRNA(CAGGln) genes from the yeast Saccharomyces cerevisiae can partially suppress a number of yeast ochre and amber mutations, respectively. In the present study we show that the tRNA(CAGGln) gene can also function as a weak amber suppressor when expressed in cells at physiological levels. This observation is consistent with a role of tRNA(CAGGln) as an evolutionary progenitor of tRNAs that strongly decode UAG codons.
Anti-idiotype immunization of cancer patients: modulation of the immune response.
Authors: Herlyn D , Wettendorff M , Schmoll E , Iliopoulos D , Schedel I , Dreikhausen U , Raab R , Ross A H , Jaksche H , Scriba M
Published: May 2006

Thirty patients with advanced colorectal carcinoma (CRC) were treated with alum-precipitated polyclonal goat anti-idiotypic antibodies (Ab2) to monoclonal anti-CRC antibody CO17-1A (Ab1) in doses between 0.5 and 4 mg per injection. All patients developed anti-anti-idiotypic antibodies (Ab3) with binding specificities on the surfaces of cultured tumor cells similar to the specificity of Ab1. Furthermore, the Ab3 competed with Ab1 for binding to CRC cells. Fractions of Ab3-containing sera obtained after elution of the serum immunoglobulins from CRC cells bound to purified tumor antigen and inhibited binding of Ab2 to Ab1. The Ab3, therefore, may share idiotopes with Ab1. Six patients showed partial clinical remission and seven patients showed arrest of metastases following immunotherapy. Four of the thirteen patients with measurable clinical responses had received Ab2 alone, whereas 9 patients had also received chemotherapy.
Predominant role of amino-terminal sequences in dictating efficiency of class II major histocompatibility complex alpha beta dimer expression.
Authors: Sant A J , Braunstein N S , Germain R N
Published: May 2006

Cell surface expression of class II major histocompatibility complex-encoded (Ia) molecules depends on association of the component alpha and beta chains into a stable heterodimer. In the mouse, two isotypes of class II molecules have been identified, A beta A alpha and E beta E alpha. However, experiments from this laboratory have shown that, following DNA-mediated gene transfer into murine L cells, an A beta E alpha-mixed-isotype molecule can be assembled and expressed at the cell surface. In the present study, we have investigated the structural features of the beta chain that control the extent of association and level of membrane expression of A beta E alpha interisotypic pairs. The use of intact allelic A beta genes demonstrated that only A beta d chains, but not A beta b or A beta k chains, can be coexpressed on the surface membrane with E alpha chains. Transfection of recombinant A beta genes that encode all or half of the beta 1 domain from one allele and the rest of the chain from another allele revealed that the 5-7 polymorphic residues in the amino-terminal 50 residues of the A beta chain completely controlled this variation in expression with E alpha. Isotypically mixed beta genes encoding the A beta 1 domain of either A beta d or A beta k chains and the beta 2, transmembrane, and intracytoplasmic portions of E beta chains were used to assess the role of isotypically conserved structures in alpha beta pairing and expression. In marked contrast to the major alterations in expression accompanying changes in the amino-terminal polymorphic residues, exchange of these carboxyl-terminal isotypic segments had no detectable influence on the efficiency of expression with either A alpha or E alpha chains. These results argue strongly that variations in the efficiency with which distinct Ia alpha beta dimers assemble and are transported to the membrane is determined almost exclusively by a critical chain interaction involving the amino-terminal domains of the molecules.
Inhibition of human immunodeficiency virus syncytium formation and virus replication by castanospermine.
Authors: Walker B D , Kowalski M , Goh W C , Kozarsky K , Krieger M , Rosen C , Rohrschneider L , Haseltine W A , Sodroski J
Published: May 2006

Castanospermine (1,6,7,8-tetrahydroxyoctahydroindolizine) is a plant alkaloid that modifies glycosylation by inhibiting alpha-glucosidase I. Castanospermine is shown to inhibit syncytium formation induced by the envelope glycoprotein of the human immunodeficiency virus and to inhibit viral replication. The decrease in syncytium formation in the presence of castanospermine can be attributed to inhibition of processing of the envelope precursor protein gp160, with resultant decreased cell surface expression of the mature envelope glycoprotein gp120. In addition, castanospermine may cause defects in steps involved in membrane fusion after binding of CD4 antigen. The antiviral effects of castanospermine may be due to modifications of the envelope glycoprotein that affect the ability of the virus to enter cells after attachment to the CD4 cell receptor.
Structure of L-3-hydroxyacyl-coenzyme A dehydrogenase: preliminary chain tracing at 2.8-A resolution.
Authors: Birktoft J J , Holden H M , Hamlin R , Xuong N H , Banaszak L J
Published: May 2006

The conformation of L-3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35) has been derived from electron-density maps calculated at 2.8-A resolution with phases obtained from two heavy-atom derivatives and the bound coenzyme, NAD. Like other dehydrogenases, 3-hydroxyacyl-CoA dehydrogenase is a double-domain structure, but the bilobal nature of this enzyme is more pronounced than has been previously observed. The amino-terminal domain, which comprises approximately the first 200 residues, is responsible for binding the NAD cofactor and displays considerable structural homology with the dinucleotide binding domains observed in other NAD-, NADP-, and FAD-dependent enzymes. The carboxyl-terminal domain, comprising the remaining 107 residues, appears to be all alpha-helical and bears little homology to other known dehydrogenases. The subunit-subunit interface in the 3-hydroxyacyl-CoA dehydrogenase dimer is formed almost exclusively by residues in the smaller helical domain. A difference map between the apo and holo forms of the crystalline enzyme has been interpreted in terms of the NAD molecule being bound in a typically extended conformation. The location of the coenzyme binding site, along with the structural homology to other dehydrogenases, makes it possible to speculate about the location of the binding site for the fatty acyl-CoA substrate.
Preparation and purification of microplasmin.
Authors: Wu H L , Shi G Y , Bender M L
Published: May 2006

A catalytically active, human microplasmin was produced by incubation of [Lys]plasmin in buffer at pH 11.0 for up to 12 hr. The microplasmin was purified by affinity chromatography that used lysine-Sepharose and soybean trypsin inhibitor-Sepharose columns. It is homogeneous and pure by electrophoretic analysis in NaDodSO4/polyacrylamide gels and by gel filtration on a Superose 12 column. The molecular weight of the microplasmin determined by NaDodSO4 gel electrophoresis is 29,000 and 26,500 under reducing condition, whereas the molecular weight of native plasmin is 76,500. Microplasmin consists mainly of the ligh (B) chain of native human plasmin and possesses one active site per protein molecule when titrated with p-nitrophenyl p'-guanidinobenzoate. Microplasmin hydrolyzes the peptide substrate NH2-D-Val-Leu-Lys-p-nitroanilide (S-2251) with a Km of 0.361 +/- 0.017 mM and a kcat of 40.3 +/- 3.3 s-1 at pH 7.4 and 37 degrees C, whereas native plasmin has a Km of 0.355 +/- 0.002 mM and a kcat of 27.9 +/- 0.3 s-1 under the same conditions.
Biological and physical properties of a model calcitonin containing a glutamate residue interrupting the hydrophobic face of the idealized amphiphilic alpha-helical region.
Authors: Green F R , Lynch B , Kaiser E T
Published: May 2006

2A new calcitonin analogue, model calcitonin III (MCt-III), has been synthesized, and its biological and physical characteristics have been studied. This analogue has an idealized alpha-helix from residue 8-22 with glutamate at position 15 interrupting an otherwise continuous surface of aliphatic side chains (those of leucine residues) on the hydrophobic face of the helix. MCt-III differs from a previous model, MCt-II, only by the substitution Leu15----Glu and is here compared with salmon calcitonin I (sCt-I) and MCt-II to elucidate further the role of the putative amphiphilic alpha-helix in determining biological and physical properties of the hormone. MCt-III shows physical properties intermediate between those of sCt-I and MCt-II, demonstrating the influence of appropriately positioned single residues on properties of amphiphilic structures. In our two biological assays, a brain-binding assay and an in vivo hypocalcemic assay, MCt-III reproduces the sigmoidal dose-response curves of sCt-I; this contrasts with the behavior of MCt-II, which demonstrated unusual dose-response curves in these two assays. MCt-III is almost three times more potent than sCt-I in our hypocalcemic assay; this activity groups MCt-III among the most potent known analogues of sCt-I.
Learning algorithms and probability distributions in feed-forward and feed-back networks
Authors: Hopfield J. J.
Published: May 2006

Learning algorithms have been used both on feed-forward deterministic networks and on feed-back statistical networks to capture input-output relations and do pattern classification. These learning algorithms are examined for a class of problems characterized by noisy or statistical data, in which the networks learn the relation between input data and probability distributions of answers. In simple but nontrivial networks the two learning rules are closely related. Under some circumstances the learning problem for the statistical networks can be solved without Monte Carlo procedures. The usual arbitrary learning goals of feed-forward networks can be given useful probabilistic meaning.
Opiate receptors and the endorphin-mediated cardiovascular effects of clonidine in rats: evidence for hypertension-induced mu-subtype to delta-subtype changes.
Authors: Mosqueda-Garcia R , Kunos G
Published: May 2006

Effects of opiate receptor antagonists on centrally mediated cardiovascular responses to clonidine and beta-endorphin were studied in urethane-anesthetized spontaneously hypertensive Okamoto-Aoki rats (SHR), normotensive Sprague-Dawley rats, and Sprague-Dawley rats made hypertensive with deoxycorticosterone pivalate/salt. Microinjection of 270 pmol of naloxone into the nucleus tractus solitarii (NTS) significantly inhibited the hypotensive and bradycardic response to 5 nmol of similarly administered clonidine in both SHR and normotensive Sprague-Dawley rats. In SHR, a similar inhibition was observed after the delta-opiate receptor antagonist ICI 174864, but not after the mu-receptor antagonist beta-funaltrexamine (both at 270 pmol, intra-NTS), whereas in normotensive Sprague-Dawley rats, beta-funaltrexamine, but not ICI 174864, was an effective inhibitor. The same pattern of differential inhibition was seen when clonidine was given i.v. and the opiate antagonists were given intracisternally in SHR and Sprague-Dawley rats. Intra-NTS microinjection of 280 fmol of beta-endorphin caused hypotension and bradycardia, and these effects were similarly inhibited by ICI 174864 in SHR and by beta-funaltrexamine in Sprague-Dawley rats. In Sprague-Dawley rats made hypertensive by chronic administration of deoxycorticosterone pivalate and salt, the hypotensive and bradycardic effects of intra-NTS clonidine were inhibited by ICI 174864, but not by beta-funaltrexamine, a pattern similar to that in SHR, but different from that in normotensive Sprague-Dawley rats. These results support the hypothesis that beta-endorphin release and subsequent stimulation of opiate receptors in the NTS are involved in the cardiovascular effects of clonidine in rats. These results further suggest, however, that hypertension regulates the subtype of opiate receptors mediating these effects.
Kinetic differences between Na channels in the egg and in the neurally differentiated blastomere in the tunicate.
Authors: Okamura Y , Shidara M
Published: May 2006

In the tunicate embryo, the cleavage can be arrested at any stage by treatment with cytochalasin B, and yet treated blastomeres can express differentiated phenotypes after a certain period of incubation. We took advantage of these large differentiated blastomeres, which were amenable to electrophysiological recordings, to compare Na channels in the egg cell and those in the neurally differentiated blastomere. The macroscopic Na current in the differentiated blastomere showed a marked slow-decaying component in addition to a fast one, whereas in the egg the fast-decaying component was predominant. Both the I-V relationship and the steady-state inactivation curve shifted about 8 mV in the positive direction in the neurally differentiated blastomere compared with those in the egg cell. Furthermore, single-channel current recordings revealed that Na channels reopened more frequently in the differentiated blastomere than in the egg cell. This characteristic of the channel corresponded well to the marked slow-decaying component of the macroscopic current in the differentiated blastomere. The single-channel conductance was similar in both types of cells. We conclude that the neurally differentiated blastomere expresses a Na channel that has properties of inactivation kinetics distinct from those of the egg-type Na channel and that no detectable egg-type channel coexists in the neurally differentiated blastomeres.
Arabinose-induced binding of AraC protein to araI2 activates the araBAD operon promoter.
Authors: Lee N , Francklyn C , Hamilton E P
Published: May 2006

The state of Escherichia coli araI DNA occupancy by AraC protein has been found to change from a two-turn to a four-turn occupancy upon the addition of the inducer arabinose. The araI site is separable into two contiguous regions, araI1 and araI2. araI1 binds both ligand-bound and ligand-free AraC protein, whereas araI2 binds AraC protein in the presence of arabinose only. A mutation in araI and a known mutation in araC led to the loss of araI2 binding, while binding to araI1 was unaffected. Both mutants failed to activate the promoter of the araBAD operon. We propose that araI2 occupancy by AraC protein leads to RNA polymerase recognition of the araBAD promoter and that araI1 acts as a switch mechanism allowing both the repressor and the activator forms of AraC protein to regulate the araBAD promoter.
RAD3 protein of Saccharomyces cerevisiae is a DNA helicase.
Authors: Sung P , Prakash L , Matson S W , Prakash S
Published: May 2006

The Saccharomyces cerevisiae RAD3 gene, which is required for cell viability and excision repair of damaged DNA, encodes an 89-kDa protein that has a single-stranded DNA-dependent ATPase activity. We now show that the RAD3 protein also possesses a helicase activity that unwinds duplex regions in DNA substrates constructed by annealing DNA fragments of 71-851 nucleotides to circular, single-stranded M13 DNA. The DNA helicase activity is dependent on the hydrolysis of ATP, has a pH optimum of approximately 5.6, and is inhibited by antibodies raised against a truncated RAD3 protein produced in Escherichia coli. The RAD3 helicase translocates along single-stranded DNA in the 5'----3' direction. The direction of RAD3 helicase movement is consistent with the possibility that it unwinds DNA duplexes in advance of the replication fork during DNA replication.
Twisting of fibrin fibers limits their radial growth.
Authors: Weisel J W , Nagaswami C , Makowski L
Published: May 2006

Electron microscopy of freeze-dried, shadowed fibrin fibers has demonstrated that these structures are twisted. The pitch and radius of many fibers were measured from the micrographs. Although there is some variability, the average pitch of 1930 +/- 280 (SD) nm is independent of radius. The distribution of observed radii of fibers assembled in vitro is highly skewed, suggesting that individual fibers grow to a maximum radius of about 50 nm, except when both pH and ionic strength are high; fibers aggregate to form thicker fiber bundles under some conditions. The observed twisting may be responsible for limiting the lateral growth of individual fibers. Protofibrils near the surface of a twisted fiber are stretched relative to those near the center. Consequently, the degree to which a protofibril can be stretched limits the radius of a fiber; protofibrils can be added to a growing fiber until the energy required to stretch an added protofibril exceeds the energy of binding. These properties of assembly arise directly from the intrinsic twist of the fibrinogen molecule determined from structural evidence. Simple geometric considerations lead to conclusions regarding the locations of the binding sites for assembly of the protofibril and the flexibility of the fibrin molecule.
Coupling of inositol phospholipid hydrolysis to peptide hormone receptors expressed from adrenal and pituitary mRNA in Xenopus laevis oocytes.
Authors: McIntosh R P , Catt K J
Published: May 2006

The expression of several neurotransmitter and drug receptors from injected exogenous mRNA in Xenopus laevis oocytes has been demonstrated by electrophysiological measurements of ion channel activation. The expression of specific receptors for peptide hormones in such a translation system would facilitate studies on the structure and regulation of cell-surface receptors as well as their coupling to membrane transduction mechanisms. The expression of receptors for calcium-mobilizing hormones in Xenopus oocytes was sought by analysis of phospholipid turnover in hormone-stimulated oocytes. For this purpose, Xenopus oocytes were injected with mRNA extracted from bovine adrenal and pituitary glands and incubated with myo-[3H]inositol to label plasma-membrane phosphatidylinositol phosphates. The expression of functionally active receptors for angiotensin II (AII) and thyrotropin-releasing hormone (TRH) was demonstrated by the stimulation of [3H]inositol phosphate production by AII and TRH in the mRNA-injected, [3H]inositol-prelabeled oocytes. The ability of AII and TRH to act by way of newly synthesized receptors from mammalian endocrine tissues to stimulate phosphatidylinositol polyphosphate hydrolysis in Xenopus oocytes suggests a generalized and conserved mechanism of receptor coupling to the transduction mechanism responsible for activation of phospholipase C in the plasma membrane.
Biochemical correlates of short-term sensitization in Aplysia: temporal analysis of adenylate cyclase stimulation in a perfused-membrane preparation.
Authors: Yovell Y , Kandel E R , Dudai Y , Abrams T W
Published: May 2006

During short-term sensitization, a simple form of nonassociative learning in Aplysia, the presentation of a single brief noxious stimulus results in enhancement of the defensive withdrawal reflex lasting minutes to tens of minutes. This behavioral plasticity involves presynaptic facilitation of synaptic transmission from the mechanosensory neurons that mediate the reflex to their central target cells. This facilitation is due to cAMP-dependent protein phosphorylation. To determine whether the time course of presynaptic facilitation might be due to a persistent increase in activity of adenylate cyclase (EC 4.6.1.1) itself, persistence of the transmitter, or yet other processes, we developed a perfused-membrane method to analyze the time course of activation of adenylate cyclase by transient stimuli. After stimulation by a pulse of stimulatory transmitter, activation of adenylate cyclase decayed within 60 sec. This finding indicates that the enzyme does not remain persistently active in the absence of transmitter and suggests that short-term retention is likely to be due to other mechanisms. Possible additional mechanisms include continued activation of the cyclase by transmitter, cellular factors extrinsic to the cyclase that prolong the time course of its activation, and persistence of processes downstream from the cyclase.
Intracellular biochemical manipulation of phototransduction in detached rod outer segments.
Authors: Sather W A , Detwiler P B
Published: May 2006

Recent progress in understanding phototransduction has come primarily from studies on cell-free systems. To investigate the transduction process under physiological conditions, a fully functional preparation of retinal rod outer segments without attached inner segments was developed that allows electrical recording of light-sensitive current during intracellular dialysis with defined solutions. No light-sensitive current is recorded from detached outer segments dialyzed with nucleotide-free solutions, whereas cells detached from the retina into Ringer's solution containing 3-isobutyl-1-methyl-xanthine (a phosphodiesterase inhibitor) develop a light-sensitive inward dark current. This indicates that there is a basal level of cGMP-specific phosphodiesterase activity in the dark. Detached outer segments dialyzed with greater than or equal to 20 microM cGMP rapidly develop a light-suppressible current. A current of similar magnitude is generated more slowly during dialysis with a 50-fold greater concentration of GTP. Apparently, cGMP can be synthesized from GTP by guanylate cyclase in the outer segment. Cells dialyzed with cGMP alone show a reduced light sensitivity that is restored to normal by addition of 20 microM GTP. This action of GTP is antagonized by guanosine 5'-[beta-thio]diphosphate. These findings are in good agreement with biochemical evidence indicating that a GTP-binding protein (transducin) plays a pivotal role in the generation of responses to light. The recovery of photocurrent following a brief flash is delayed or abolished by dialysis with solutions that lack ATP or contain guanosine 5'-[gamma-thio]triphosphate, a nonhydrolyzable GTP analog. These results support the view that both GTP hydrolysis by activated transducin and ATP-dependent phosphorylation of a rhodopsin photoproduct are necessary for termination of the transduction process.
Alkanol effects on early potassium currents in Aplysia neurons depend on chain length.
Authors: Treistman S N , Wilson A
Published: May 2006

The relationship between alkanol chain length and effects on the transient potassium current, IA, were examined in three identified Aplysia californica neurons with ethanol (EtOH), butanol (BuOH), and hexanol (HxOH). Qualitative differences were found when the actions of EtOH were compared with those of the longer-chain-length alcohols. Whereas EtOH primarily affected the decay time constant of IA, having minimal effects on amplitude, BuOH and HxOH exerted their major effect on the amplitude of IA, reducing it, while their effects on decay kinetics were much less pronounced. The effects of EtOH on IA decay are cell specific among identified neurons of the Aplysia nervous system. The actions of BuOH and HxOH did not mimic these interneuronal differences. These data, coupled with data previously reported by us and others, make it unlikely that EtOH exerts its actions on IA via perturbation of a bulk lipid phase within the membrane.
Expression of the nuclear gene encoding oxygen-evolving enhancer protein 2 is required for high levels of photosynthetic oxygen evolution in Chlamydomonas reinhardtii.
Authors: Mayfield S P , Rahire M , Frank G , Zuber H , Rochaix J D
Published: May 2006

We have cloned a cDNA encoding a 20-kDa polypeptide, oxygen-evolving enhancer protein 2 (OEE2), in Chlamydomonas reinhardtii. This polypeptide has been implicated in photosynthetic oxygen evolution, and it is associated with the photosystem II complex, the site of oxygen evolution in all higher plants and algae. The sequence of OEE2 cDNA, the deduced amino acid sequence of the preprotein, the N-terminal protein sequence of mature OEE2 protein, and the coding regions of the single OEE2 gene are presented. The protein is synthesized with a 57-amino acid N-terminal transit peptide that directs the transport of this polypeptide across three cellular membranes. A nuclear mutant of C. reinhardtii, deficient in oxygen-evolving activity, is shown to be specifically missing OEE2 polypeptides. This mutation, which results in the complete absence of all OEE2 mRNA and protein, does not affect the accumulation of other photosystem II polypeptides or their mRNAs.
Constitutive and anaerobically induced DNase-I-hypersensitive sites in the 5′ region of the maize
Adh1
gene
Authors: Paul Anna-Lisa , Vasil Vimla , Vasil Indra K. , Ferl Robert J.
Published: May 2006

DNase-I-hypersensitive sites have been characterized in a plant gene, maize
Adh1
(which encodes alcohol dehydrogenase 1). It has been generally recognized in animal genes that the chromatin of the 5′ flanking region can be characterized by the accessibility of its DNA to the nuclease DNase I (EC 3.1.21.1), indicating which areas in the promoter are “open” to nuclear factors. The 5′ region of the maize
Adh1
gene contains two distinct DNase-I-hypersensitive regions, one constitutively present from position -160 to -700 and one that is anaerobically induced from position -35 to -150. The constitutive region contains three major hypersensitive sites, one of which corresponds in part to a region of potential Z-DNA. The induced hypersensitive region includes TATAA at -38 and CAAT at -100 as well as other potential regulatory sequences.
Na+ channels as sites of action of the cardioactive agent DPI 201-106 with agonist and antagonist enantiomers.
Authors: Romey G , Quast U , Pauron D , Frelin C , Renaud J F , Lazdunski M
Published: May 2006

This paper shows the interaction of the cardiotonic agent 4-[3-(4-diphenylmethyl-1-piperazinyl)-2-hydroxypropoxy]-1H-indole- 2-carbonitrile (DPI 201-106) and its optic enantiomers R-DPI (205-429) and S-DPI (205-430) with the Na+ channel of a variety of excitable cells. Voltage-clamp experiments show that DPI 201-106 acts on neuroblastoma cells and rat cardiac cells. S-DPI (205-430) increases the peak Na+ current, slows down the kinetics of Na+ channel inactivation, and is cardiotonic on heart cells. Conversely, R-DPI (205-429) reduces the peak Na+ current and blocks Na+ channel activity and cardiac contractions. Binding experiments using radioactively labeled toxins indicate that DPI 201-106 and its enantiomers do not interact with sites already identified for tetrodotoxin or sea anemone and scorpion toxins. DPI 201-106 and its enantiomers inhibit binding of a 3H-labeled batrachotoxin derivative, [3H]batrachotoxinin A 20-alpha-benzoate, to brain membranes. The dissociation constant of the complex formed between the Na+ channel and both R-DPI and S-DPI is Kd congruent to 100 nM. 22Na+ uptake experiments using different cell types have shown that R and S enantiomers of DPI 201-106 are active on the different Na+ channel subtypes with similar IC50 values. These results are discussed in relation with the cardiotonic properties of DPI 201-106 that are not accompanied by cardiotoxic effects.
Pulmonary surfactant and its components inhibit secretion of phosphatidylcholine from cultured rat alveolar type II cells.
Authors: Dobbs L G , Wright J R , Hawgood S , Gonzalez R , Venstrom K , Nellenbogen J
Published: May 2006

Pulmonary surfactant is synthesized and secreted by alveolar type II cells. Radioactive phosphatidylcholine has been used as a marker for surfactant secretion. We report findings that suggest that surfactant inhibits secretion of 3H-labeled phosphatidylcholine by cultured rat type II cells. The lipid components and the surfactant protein group of Mr 26,000-36,000 (SP 26-36) inhibit secretion to different extents. Surfactant lipids do not completely inhibit release; in concentrations of 100 micrograms/ml, lipids inhibit stimulated secretion by 40%. SP 26-36 inhibits release with an EC50 of 0.1 microgram/ml. At concentrations of 1.0 microgram/ml, SP 26-36 inhibits basal secretion and reduces to basal levels secretion stimulated by terbutaline, phorbol 12-myristate 13-acetate, and the ionophore A23187. The inhibitory effect of SP 26-36 can be blocked by washing type II cells after adding SP 26-36, by heating the proteins to 100 degrees C for 10 min, by adding antiserum specific to SP 26-36, or by incubating cells in the presence of 0.2 mM EGTA. SP 26-36 isolated from canine and human sources also inhibits phosphatidylcholine release from rat type II cells. Neither type I collagen nor serum apolipoprotein A-1 inhibits secretion. These findings are compatible with the hypothesis that surfactant secretion is under feedback regulatory control.