Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “complexity”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 469 records · Page 26Linked to original sources
PubMed2005

Structure determination of GGA-GAE and gamma1-ear in complex with peptides: crystallization of low-affinity complexes in membrane traffic.

Crystallization of protein-protein complexes is an important step in the studies of biological functions of proteins. However, weak and transient, even though specific, interactions often present difficulties in crystallization of protein complexes due to the heterogeneity of the sample mixture. For example, the gamma1-ear domain of the AP-1 complex and the GAE domain of GGA1, responsible for the interaction with accessory proteins involved in vesicular transport, are known to interact with target proteins with affinities of the order of 1-100 microM. Such low affinities have hampered crystallization trials of the complexes. To overcome this problem, the gamma1-ear and GAE domains were first co-crystallized with excess amounts of the peptides. Co-crystals of both domains were obtained and the complex structures were determined at 2.5-2.9 A resolution. Based on the crystal packing of gamma1-ear and the cognate peptide, gamma1-ear fused with a peptide tag at the N-terminus was prepared. The peptide-tagged gamma1-ear readily crystallized and the crystal diffracted far better, 1.9-2.2 A resolution, compared with the co-crystallized complex, giving significantly more details without affecting the overall complex structure.

ADP-Ribosylation Factors↗
PubMed1997

X-ray studies on crystalline complexes involving amino acids and peptides. XXXII. Effect of chirality on ionisation state, stoichiometry and aggregation in the complexes of oxalic acid with DL- and L-lysine.

Crystals of the oxalic acid complex of DL-lysine (triclinic P1; a = 5.540(1), b = 10.764(2), c = 12.056(2) A, alpha = 77.8(1), beta = 80.6(1), gamma = 75.6(1).; R = 4.7% for 2023 observed reflections) contain lysine and semioxalate ions in the 1:1 ratio, whereas the ratio of lysine and semioxalate/oxalate ions is 2:3 in the crystals of the L-lysine complex (monoclinic P2(1); alpha = 4.906(1), b = 20.145(4), c = 12.455(1) A, beta = 92.5(1).; R = 4.4% for 1494 observed reflections). The amino acid molecule in the L-lysine complex has an unusual ionisation state with positively charged alpha- and side-chain amino groups and a neutral carboxyl group. The unlike molecules aggregate into separate alternating layers in the DL-lysine complex in a manner similar to that observed in several of the amino acid complexes. The L-lysine complex exhibits a new aggregation pattern which cannot be easily explained in terms of planar features, thus emphasizing the fundamental dependence of aggregation on molecular characteristics. Despite the differences in stoichiometry, ionisation state and long-range aggregation patterns, the basic element of aggregation in the two complexes exhibits considerable similarity.

Amino Acids↗
PubMed1996

Differences in the serum levels of acetaldehyde and cytotoxic acetaldehyde-albumin complexes after the consumption of red and white wine: in vitro effects of flavonoids, vitamin E, and other dietary antioxidants on cytotoxic complexes.

After the consumption of ethanol, acetaldehyde levels increase in the serum, and the serum develops a nondialyzable cytotoxic activity caused by the formation of unstable acetaldehyde-albumin complexes. The concentration of acetaldehyde in the serum and the cytotoxic activity in serum albumin 8.5 hr after six healthy volunteers began to drink 94 g of ethanol were significantly less when the ethanol was consumed as red wine than as white wine. The serum acetaldehyde was measured by a fluorigenic HPLC assay, and the cytotoxic activity in albumin was determined using two different assays based on dissimilar endpoints: (1) detachment of adherent A9 cells and (2) impairment of the ability of A9 cells to reduce tetrazolium. When serum obtained from five other healthy volunteers after the consumption of white wine was incubated at 37 degrees C for 3 hr with a number of dietary antioxidants at a concentration of 100 mumol/liter, the cytotoxicity of the albumin was markedly reduced. The antioxidants studied consisted of six flavonoids (kaempherol, fisetin, quercetin catechin, taxifolin, and coumarin) and three nonflavonoids (salicylic acid, tannic acid, and alpha-tocopherol). In the cases of alpha-tocopherol, a statistically significant reduction of cytotoxicity was observed at a concentration of 10 mumol/liter. In addition, the cytotoxicity of artificially prepared acetaldehyde-albumin complexes was significantly reduced when such complexes were incubated with 50 to 100 mumol/liter of kaempherol, fisetin, quercetin, coumarin or salicylic acid, or 10 mumol/liter of alpha-tocopherol at 37 degrees C for 3 hr. Evidently, in vitro, flavonoid and nonflavonoid dietary constituents reduce the amount of unstable acetaldehyde-albumin complexes found in both postalcohol serum and in artificially produced acetaldehyde-albumin complexes. The difference in the amount of unstable acetaldehyde-albumin complexes found in serum after the consumption of red and white wine may therefore be caused by the higher concentration of antioxidants, including flavonoids, in red wine than in white wine. Because acetaldehyde and acetaldehyde-albumin complexes have been implicated in the pathogenesis of alcohol-mediated tissue damage, these data suggest that dietary antioxidants may influence the biological consequences of excess alcohol consumption.

Acetaldehyde↗
PubMed1998

Perceptual segregation and pitch shifts of mistuned components in harmonic complexes and in regular inharmonic complexes.

It is unclear whether the perceptual segregation of a mistuned harmonic from a periodic complex tone depends specifically on harmonic relations between the other components. A procedure used previously for harmonic complexes [W. M. Hartmann et al., J. Acoust. Soc. Am. 88, 1712-1724 (1990)] was adapted and extended to regular inharmonic complexes. On each trial, subjects heard a 12-component complex followed by a pure tone in a continuous loop. In experiment 1, a mistuning of +/- 4% was applied to one of the components 2-11. The complex was either harmonic, frequency shifted, or spectrally stretched. Subjects adjusted the pure tone to match the pitch of the mistuned component. Near matches were taken to indicate segregation, and were almost as frequent in the inharmonic conditions as in the harmonic case. Also, small but consistent mismatches, pitch shifts, were found in all conditions. These were similar in direction and size to earlier findings for harmonic complexes. Using a range of mistunings, experiment 2 showed that the segregation of components from regular inharmonic complexes could be sensitive to mistunings of 1.5% or less. These findings are consistent with the proposal that aspects of spectral regularity other than harmonic relations can also influence auditory grouping.

Acoustic Stimulation↗
PubMed2005

Chemical activation of pre-Bötzinger complex in vivo reduces respiratory network complexity.

In the in vivo anesthetized adult cat model, multiple patterns of inspiratory motor discharge have been recorded in response to chemical stimulation and focal hypoxia of the pre-Bötzinger complex (pre-BötC), suggesting that this region may participate in the generation of complex respiratory dynamics. The complexity of a signal can be quantified using approximate entropy (ApEn) and multiscale entropy (MSEn) methods, both of which measure the regularity (orderliness) in a time series, with the latter method taking into consideration temporal fluctuations in the underlying dynamics. The current investigation was undertaken to examine the effects of pre-BötC-induced excitation of phasic phrenic nerve discharge, which is characterized by high-amplitude, rapid-rate-of-rise, short-duration bursts, on the complexity of the central inspiratory neural controller in the vagotomized, chloralose-anesthetized adult cat model. To assess inspiratory neural network complexity, we calculated the ApEn and MSEn of phrenic nerve bursts during eupneic (basal) discharge and during pre-BötC-induced excitation of phasic inspiratory bursts. Chemical stimulation of the pre-BötC using DL-homocysteic acid (DLH; 10 mM; 10-20 nl; n=10) significantly reduced the ApEn from 0.982+/-0.066 (mean+/-SE) to 0.664+/-0.067 (P<0.001) followed by recovery ( approximately 1-2 min after DLH) of the ApEn to 1.014+/-0.067; a slightly enhanced magnitude reduction in MSEn was observed. Focal pre-BötC hypoxia (induced by sodium cyanide; NaCN; 1 mM; 20 nl; n=2) also elicited a reduction in both ApEn and MSEn, similar to those observed for the DLH-induced response. These observations demonstrate that activation of the pre-BötC reduces inspiratory network complexity, suggesting a role for the pre-BötC in regulation of complex respiratory dynamics.

Animals↗
PubMed2005

Isolated integrin beta3 subunit cytoplasmic domains require membrane anchorage and the NPXY motif to recruit to adhesion complexes but do not discriminate between beta1- and beta3-positive complexes.

Integrin adhesion receptors consist of non-covalently linked alpha and beta subunits each of which contains a large extracellular domain, a single transmembrane domain and a short cytoplasmic tail. Engaged integrins recruit to focal structures globally termed adhesion complexes. The cytoplasmic domain of the beta subunit is essential for this clustering. beta1 and beta3 integrins can recruit at distinct cellular locations (i.e. fibrillar adhesions vs focal adhesions, respectively) but it is not clear whether individual beta subunit cytoplasmic and transmembrane domains are by themselves sufficient to drive orthotopic targeting to the cognate adhesion complex. To address this question, we expressed full-length beta3 transmembrane anchored cytoplasmic domains and truncated beta3 cytoplasmic domains as GFP-fusion constructs and monitored their localization in endothelial cells. Membrane-anchored full-length beta3 cytoplasmic domain and a beta3 mutant lacking the NXXY motif recruited to adhesion complexes, while beta3 mutants lacking the NPXY and NXXY motifs or the transmembrane domain did not. Replacing the natural beta subunit transmembrane domain with an unrelated (i.e. HLA-A2 alpha chain) transmembrane domain significantly reduced recruitment to adhesion complexes. Transmembrane anchored beta3 and cytoplasmic domain constructs, however, recruited without discrimination to beta1- and beta3-rich adhesions complexes. These findings demonstrate that membrane anchorage and the NPXY (but not the NXXY) motif are necessary for beta3 cytoplasmic domain recruitment to adhesion complexes and that the natural transmembrane domain actively contributes to this recruitment. The beta3 transmembrane and cytoplasmic domains alone are insufficient for orthotopic recruitment to cognate adhesion complexes.

Amino Acid Motifs↗
PubMed2002

Presentation of a major histocompatibility complex class 1-binding peptide by monocyte-derived dendritic cells incorporating hydrophobized polysaccharide-truncated HER2 protein complex: implications for a polyvalent immuno-cell therapy.

Recognition of the essential role of dendritic cells (DCs) as professional antigen-presenting cells has prompted investigators to search for methods to use DCs as natural adjuvants in immunotherapy. A number of antigenic oligopeptides, recognized by CD8(+) cytotoxic T lymphocytes (CTLs) specific for cancer cells, have been applied in clinical trials using DCs. Such a monovalent vaccine with a single epitope for a particular type of HLA class 1 molecule would be effective. However, a polyvalent vaccine might be more potent. We designed a novel protein delivery system consisting of hydrophobized polysaccharides complexed with target proteins. The truncated HER2 protein encompassing 147 N-terminal amino acids, including the 9-mer HER2p63-71 peptide (HER2p63), TYLPTNASL, the human homologue of an antigenic murine tumor rejection peptide, was prepared. We report here that HLA-A2402(+) DCs could incorporate hydrophobized polysaccharide-truncated HER2 protein complexes and process the protein to present major histocompatibility complex class 1-binding HER2p63 peptide. The complexes enter DCs by phagocytosis, and then the truncated protein is processed through a pathway similar to that for endogenous proteins. DCs sensitized by these complexes primed and boosted HER2p63-specific CD8(+) T cells in the context of HLA-A2402. Vaccination with DCs incorporating these complexes completely suppressed lung metastases in a HER2-expressing murine tumor model. We also generated 3 CD4(+) clones reactive with different HER2- derived 25-mer peptides from lymph node cells in mice treated with CHP/HER2-147. Thus, hydrophobized polysaccharide-protein complexes are promising candidates for the construction of polyvalent vaccines.

Amino Acid Sequence↗
PubMed2002

Transcriptional activation of human CYP17 in H295R adrenocortical cells depends on complex formation among p54(nrb)/NonO, protein-associated splicing factor, and SF-1, a complex that also participates in repression of transcription.

The first 57 bp upstream of the transcription initiation site of the human CYP17 (hCYP17) gene are essential for both basal and cAMP-dependent transcription. EMSA carried out by incubating H295R adrenocortical cell nuclear extracts with radiolabeled -57/-38 probe from the hCYP17 promoter showed the formation of three DNA-protein complexes. The fastest complex contained steroidogenic factor (SF-1) and p54(nrb)/NonO, the intermediate complex contained p54(nrb)/NonO and polypyrimidine tract-binding protein-associated splicing factor (PSF), and the slowest complex contained an SF-1/PSF/p54(nrb)/NonO complex. (Bu)(2)cAMP treatment resulted in a cAMP-inducible increase in the binding intensity of only the upper complex and also activated hCYP17 gene transcription. SF-1 coimmunoprecipitated with p54(nrb)/NonO, indicating direct interaction between these proteins. Functional assays revealed that PSF represses basal transcription. Further, the repression of hCYP17 promoter-reporter construct luciferase activity resulted from PSF interacting with the corepressor mSin3A. Trichostatin A attenuated the inhibition of basal transcription, suggesting that a histone deacetylase interacts with the SF-1/PSF/p54(nrb)/NonO/mSin3A complex. Our studies lend support to the idea that the balance between transcriptional activation and repression is essential in the control of adrenocortical steroid hormone biosynthesis.

Adrenal Cortex↗
PubMed2000

Effects of cationic charge on three-dimensional structures of intercalative complexes: structure of a bis-intercalated DNA complex solved by MAD phasing.

We characterize intercalative complexes as either "high charge" and "low charge". In low charge complexes, stacking interactions appear to dominate stability and structure. The dominance of stacking is evident in structures of daunomycin, nogalamycin, ethidium, and triostin A/echinomycin. By contrast in a DNA complex with the tetracationic metalloporphyrin CuTMPyP4 [copper (II) meso-tetra(N-methyl-4-pyridyl)porphyrin], electrostatic interactions appear to draw the porphyrin into the duplex interior, extending the DNA along its axis, and unstacking the DNA. Similarly, DNA complexes of tetracationic ditercalinium and tetracationic flexi-di show significant unstacking. Here we report x-ray structures of complexes of the tetracationic bis-intercalator D232 bound to DNA fragments d(CGTACG) and d(BrCGTABrCG). D232 is analogous to ditercalinium but with three methylene groups inserted between the piperidinium groups. The extension of the D232 linker allows it to sandwich four base pairs rather than two. In comparison to CuTMPyP4, flexi-di and ditercalinium, stacking interactions of D232 are significantly improved. We conclude that it is not sufficient to characterize intercalators simply by net charge. One anticipates strong electrostatic forces when cationic charge is focused to a small volume or region near DNA and so must consider the extent to which cationic charge is focused or distributed. In sum, ditercalinium, with a relatively short linker, focuses cationic charge more narrowly than does D232. So even though the net charges are equivalent, electrostatic charges are expected to be of greater structural significance in the ditercalinium complex than in the D232 complex.

Cations↗
PubMed1989

Recombinant TGF-beta 1 is synthesized as a two-component latent complex that shares some structural features with the native platelet latent TGF-beta 1 complex.

The entire coding region of the human transforming growth factor beta 1 (TGF-beta 1) precursor cDNA has been stably expressed in a human renal carcinoma cell line. Like platelet TGF-beta 1, the recombinant TGF-beta 1 is secreted in a biologically latent form. Immunoblot analysis and gel-filtration indicate that the recombinant latent TGF-beta 1 is a 100-kDa complex in which active 25-kDa TGF-beta 1 is noncovalently associated with the remaining 75 kDa of the processed precursor. Unlike the platelet latent complex, the recombinant latent complex contains no 135-kDa component. Thus, the processed precursor peptide alone is sufficient to confer latency on active TGF-beta 1, and the 135-kDa platelet component has a different role. The processed precursor is similarly glycosylated in recombinant and platelet complexes, and in both has an exposed heparin binding site that may be involved in targeting of the latent complex. Finally, acid activation of recombinant and platelet complexes is reversible, suggesting that the activation process does not cause major structural modifications in the components of the latent complex.

Binding Sites↗
PubMed1992

Activation of the trans geometry in platinum antitumor complexes: a survey of the cytotoxicity of trans complexes containing planar ligands in murine L1210 and human tumor panels and studies on their mechanism of action.

The cytotoxicity of transplatinum complexes of structural formula trans-[PtCl2(L)(L')] [L = L' = pyridine or thiazole, or L = quinoline (R' = methyl; R" = methyl, phenyl, or CH2phenyl) and L' = R'R"SO] has been studied in murine L1210 and human tumor cell lines. The results confirm previous observations that use of a sterically hindered planar ligand greatly enhances cytotoxicity, in comparison to trans-[PtCl2(NH3)2], such that in some cases cytotoxicity equivalent to that of the clinically used agent cisplatin [cis-[PtCl2(NH3)2]] is obtained. Results from both the panel of human ovarian carcinoma cell lines and the National Cancer Institute screening panel confirm a different pattern of cytotoxicity, with respect to cisplatin. The new trans-platinum complexes are also non-cross-resistant with cisplatin in both murine and human (human ovarian carcinoma panel) tumor cell lines. Preliminary mechanistic studies using both cis- and trans-[PtCl2(pyridine)2] in L1210 cells have been carried out, to delineate the reasons for both the dramatically enhanced cytotoxicity and the lack of cross-resistance with the clinically used agents. Intracellular uptake is enhanced for pyridine relative to ammine (NH3) complexes. The pyridine complexes also inhibit DNA synthesis, implying a role for DNA binding in their mechanism of action. Binding of the pyridine complexes to calf thymus DNA is, however, significantly less than for the analogous ammine complexes. The presence of trans-pyridine ligands results in steric hindrance, which retards the rate of reaction of trans-[PtCl2(pyridine)2], relative to trans[PtCl2(NH3)2], with other important biomolecules such as glutathione. The results point to a potential new class of platinum antitumor complexes acting by a new mechanism and with activity complementary to agents such as cisplatin.

Animals↗
PubMed1992

Covalent binding of 3'-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate (BzATP) to the isolated alpha and beta subunits and the alpha 3 beta 3 core complex of TF1. Covalent binding of BzATP prevents association of alpha and beta subunits and induces dissociation of the alpha 3 beta 3 core complex.

Binding of the photoreactive ATP analog, 3'-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate (BzATP), to the isolated alpha and beta subunits of TF1 and to the alpha 3 beta 3 "core" complex of the holoenzyme is described. About 1 mol of BzATP/mol of subunit was incorporated to isolated alpha and beta subunits. The incorporation of BzATP was prevented by ATP. Covalent binding of BzATP to the alpha subunit was in general somewhat lower than that observed with the beta subunit. No complex was formed upon mixing of either of the modified subunits with the complementary nontreated subunits. Covalent binding of 3 mol of BzATP/alpha 3 beta 3 complex completely inhibited ATPase activity and resulted in the dissociation of the complex. The labeled nucleotide analog was specifically incorporated into the beta subunit of the complex. The holoenzyme TF1, in contrast to the core complex, did not dissociate to the individual subunits upon covalent binding of BzATP. These results are discussed in relation to the location of the catalytic nucleotide binding site(s) and the conformation stability of the alpha 3 beta 3 core complex of TF1.

Adenosine Triphosphate↗
PubMed1976

Complex of D-glyceraldehyde-3-phosphate dehydrogenase with Cu2+ ion. The properties of ternary Cu-enzyme-coenzyme complex.

The formation of ternary Cu-enzyme-coenzyme complex from cupric ion and D-glyceraldehyde-3-phosphate dehydrogenase holoenzyme results in similar spectral changes as the formation of binary Cu-apoenzyme complex, which indicates that the complex bonds between cupric ion and the holoenzyme, and cupric ion and the apoenzyme are similar. Spectrophotometric titration, chemical modification experiments and inhibition studies with cupric ion gave evidence that cupric ion is selectively bound on Cys-149 residue also in the Cu-GAPD-NAD complex. The charge transfer interaction between the coenzyme and Cu-GAPD, i.e. the difference spectrum of the combination of NAD with Cu-GAPD complex, is different from that of the enzyme-coenzyme complex in the absence of cupric ion. The shape of this "modified enzyme-coenzyme charge transfer spectrum" is influenced by various anions. The difference absorption does not depend on the pH in the range of 5.5 to 9. This indicates that the bound cupric ion abolishes the effect of deprotonation of a functional group in the protein on the charge transfer interaction. It is suggested that this functional group is a histidine imidazole, which activates the Cys-149 thiol group in the native enzyme and binds the metal ion in the cupric complex in a Cys-Cu-His chelate structure.

Animals↗
PubMed1979

The formation of binary and ternary complexes of cytochrome P-450scc with adrenodoxin and adrenodoxin reductase.adrenodoxin complex. The implication in ACTH function.

Binary and ternary complexes of bovine adrenocortical mitochondrial cytochrome P-450scc with adrenodoxin and adrenodoxin reductase.adrenodoxin complex are formed in the presence of cholesterol and Emulgen 913. Both cholesterol and Emulgen 913 are required for the binding of cytochrome P-450scc with adrenodoxin. Since phospholipids are able to replace Emulgen 913 in this reaction, in vivo phospholipids of the mitochondrial inner membrane appear to play the function of the detergent. The dissociation constants of the cytochrome.adrenodoxin complex are 0.3 to 0.4 microM at 130 microM dimyristoylphosphatidylcholine and 0.9 microM at 120 microM Emulgen 913, whereas the dissociation constant for the ternary complex of cytochrome P-450scc with adrenodoxin reductase and adrenodoxin is 4.0 microM at 150 microM Emulgen 913. The stoichiometry of binary and ternary complexes reveals the 1:1 and 1:1:1 molar ratios, respectively, judging from chemical analyses after the fractionation of the complexes by gel filtration. Emulgen 913, Tween 20, ethylene glycol, myristoyllysophosphatidylcholine, dimyristoylphosphatidylcholine, and phosphatidylethanolamine show the enhanced activity of cholesterol side chain cleavage reaction with cytochrome P-450scc, adrenodoxin, adrenodoxin reductase, and NADPH. These results, in conjunction with earlier experiments, lead us to the proposal on the structure of the hydroxylase complex in the membrane and to the hypothesis on the regulation of the enzymatic activity by the availability of substrate cholesterol to the cytochrome. Hence, we propose a mobile P-450scc hypothesis for the response of the mitochondrion to adrenocorticotropic hormone stimuli.

Adrenal Cortex↗
PubMed1988

Assembly of the human T cell receptor-CD3 complex takes place in the endoplasmic reticulum and involves intermediary complexes between the CD3-gamma.delta.epsilon core and single T cell receptor alpha or beta chains.

Functionally mature human T lymphocytes express a cell-surface receptor for antigen (T cell receptor (TCR)-CD3) composed of at least six polypeptides (TCR-alpha and -beta; T3-gamma, -delta, -epsilon, and -zeta). Immature thymocytes and variants of T cell lines lacking one of the TCR.CD3 polypeptide chains fail to express surface receptor and accumulate the other chains intracellularly. Here we show that the assembly of the TCR.CD3 complex within the endoplasmic reticulum (ER) began with a core of CD3-gamma, -delta, and -epsilon to which TCR-alpha and -beta bound. A recently described intracellular protein, CD3-omega, participated in the assembly since it was found to be associated with the free TCR-alpha or -beta chains or with the CD3 chains. CD3-omega dissociated as TCR.CD3 complexes were formed in the ER. Association of non-disulfide-linked TCR-alpha and -beta chains with CD3 was detected before that of disulfide-bridged TCR-alpha/beta heterodimers. These data suggest that during assembly, the association of TCR-alpha and -beta chains with the CD3 complex precedes the formation of a TCR-alpha/beta dimer. The existence of intermediates consisting of CD3-gamma, -delta, and -epsilon chains and a single TCR-alpha or -beta chain was also confirmed by using a series of variant T cell lines lacking the TCR-beta or -alpha chain, respectively. Once the single TCR-alpha and -beta chains were associated with CD3, disulfide linkages were formed, and a 70-kDa form of the TCR was detected within the ER. This intracellular precursor of the TCR.CD3 complex was subsequently processed into the mature 90-kDa TCR as the TCR.CD3 complex passed through the Golgi apparatus. Assembly of the TCR.CD3 complex is a rather rapid process, whereas export from the ER occurs at a slow rate. After 1 h, 75% of the receptor complex remained within the ER.

Cell Line↗
PubMedDate not supplied

[Study of a protein complex from the brain which reduces actin viscosity. II. The complex inhibits elongation of actin filaments at the end preferable for polymerization and fragments the filaments].

Functional properties of the protein complex from bovine brain that shortens actin filaments are described. In the presence of Ca2+ complex shortens actin filaments and increases the initial rate of actin polymerization. In the absence of free calcium ions the complex loses its accelerating effect on actin polymerization, but still possesses actin filament shortening activity. Neither phalloidin nor tropomyosin prevent the shortening of actin filaments induced by the protein complex. Therefore the protein complex causes the fragmentation of actin filament. The data on actin polymerization in the presence of F-actin nuclei have indicated that the protein complex inhibits the elongation step of actin polymerization. The analysis of elongation in the presence of both the protein complex and cytochalasin D has demonstrated that the inhibition occurs on the fast-growing end of actin filaments.

Actins↗
PubMed1979

Complexing of reduced technetium and tin(II) by chelating phosphate compounds. II. In vitro stability of pyrophosphate and ethane-1, hydroxy-1, diphosphonate (EHDP) complexes.

The in vitro stability of 99mTc- and 113Sn-pyrophosphate and ethane-1, hydroxy-1, diphosphonate (EHDP) complexes was studied by varying the mode of preparation. The 1-hr distribution in the rat was used as an indicator for complex formation or destruction. A maximum of bone uptake and urinary excretion and a minimum of soft tissue concentration was obtained if there was an excess of phosphate in relation to tin(II) in the equilibrium. Formation of tin(II) colloid was favoured in the presence of an excess of tin(II) in the equilibrium, 99mTc colloid occurred with some delay. After dilution in neutral normal saline the chelates were more or less destroyed, as shown by a 113Sn(II) colloid formation whereas the 99mTc-phosphate complexes were transformed into a 99mTc kidney agent. At pH 11 the 113Sn(II)-phosphate complexes proved to be stable, the 99mTc-phosphate complexes were also transformed into the 99mTc kidney agent. Oxidation of all tin(II) in the equilibrium by hydrogen peroxide did not change the distribution patterns of 113Sn, 99mTc was oxidized to pertechnetate. In general complexes between tin(II) and chelating phosphate compounds proved to be more stable than those with reduced technetium. EHDP was found to form stronger complexes with tin(II) and reduced technetium than pyrophosphate.

Animals↗
PubMed1979

Microtubules and protein secretion in rat lacrimal glands. Inhibitory effect of the tubulin . colchicine complex isolated from lacrimal glands upon brain tubulin polymerization. Identification of the complex by gel electrophoresis.

The specific inhibitory effect of colchicine upon protein secretion by lacrimal glands could be related to the formation of a complex between colchicine and tubulin from the soluble fraction of the gland. By gel electrophoresis under nondissociating conditions, it is shown that this complex is similar to the colchicine . tubulin complex from brain. The complex isolated from lacrimal glands is highly inhibitory upon brain tubulin assembly since as low as 0.07 microM complex impedes the polymerization of 8 microM tubulin by 50%, compared to 3 microM for free colchicine. Therefore, a small percentage of complexed tubulin (0.9%) is enough for polymerization to be blocked. In lacrimal glands the complex might prevent the polymerization of tubulin, and colchicine shift the tubulin in equilibrium microtubules equilibrium to microtubules disassembly. The disorganization of the labile microtubular system could lead to a modification of the transport of the secretory granules and to a perturbation of secretion.

Animals↗