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At least 325 records · Page 18Linked to original sources
PubMed1978

Cross-linking of membrane phospholipid and protein using putative monofunctional imidoesters.

The reaction of methyl acetimidate or isethionyl acetimidate with mitoplasts at pH 8.5 yields two derivatives of phosphatidylethanolamine. These derivatives are shown to be the mono-amidine derivative and the bis-derivative of phosphatidylethanolamine. The bis-derivative represents one phosphatidylethanolamine cross-linked to another phosphatidylethanolamine. Similar derivatives are formed by the reaction of dipalmitoyl phosphatidylethanolamine with these imidoesters in organic solution with the exception that much more monoderivative is produced. Methyl picolinimidate reacts with phosphatidylethanolamine of mitoplasts to form primarily the mono-derivative. The bis-derivative was not detected. The reaction of bovine rod outer segment discs with methyl acetimidate causes cross-linking of 30% of the membrane rhodospin as dimers. Putative monofunctional imidoesters cause considerable cross-linking of both phospholipids and proteins in cell membranes. Cross-linking can be minimized at pH 9.0.

Animals↗
PubMed1976

DNA repair and recovery in Escherichia coli after psoralen and angelicin photosensitization.

The correlation between DNA repair and recovery of biological functions was studied using three wild type strains of Escherichia coli and two skinphotosensitizing furocoumarins, psoralen and angelicin, which are well known specific reagents of the pyrimidine bases of DNA. In addition to mono-adducts psoralen is able to form a high number of inter-strand cross-links, while angelicin forms only mono-adducts. Both of these damages were repaired, in a short time, in the following way: at first DNA was cut into small pieces that were then rejoined into molecules of normal size, free from cross-links, while the furocoumarin residue was split from DNA almost quantitatively. Recovery of biological functions was studied performing photosensitization experiments in such a manner that the same amounts of psoralen or of angelicin were linked to bacterial DNA. DNA synthesis, tested just after the damage, was inhibited in a similar extent by both drugs. The same bacteria, however, showed a very different colony-forming capacity; angelicin was much less effective than psoralen with a D37 dose about 2.7 times higher. A similar picture was obtained studying DNA synthesis at different times after photosensitization: in the bacteria damaged by angelicin it was restored while no recovery was observed in cells photosensitized by psoralen. These results suggest that both mono-adducts and cross-links can be chemically repaired more or less in a quantitative measure, but that repair of cross-links in much less effective on cell recovery; this behaviour is very probably connected with the different repair mechanisms of mono-adducts and of cross-links.

Coumarins↗
PubMed1979

Protein binding of coherin and other small molecules by thin-layer gel chromatography.

The protein binding stoichiometry of small molecules is here determined on a nanomole scale by a simplified procedure utilizing chromatography on thin layers of cross-linked dextran gels. New data are presented on the thin layer chromatographic properties of representative ligands, including a-amino acids, peptides, dyes and fluorigenic reagents, in relation to their molecular weights, polar characteristics, gel water regain values and denaturants, providing criteria for the general application of this method to studies of ligand binding with large as well as small molecules. By this procedure coherin peptides, A1 and B1--4, respectively, bind to coherin C in the molar ratio, 2:1, with a binding constant of about 10(5) M-1. Coherin C is believed to act as a carrier peptide.

Anilino Naphthalenesulfonates↗
PubMed1975

Chemical composition and biophysical properties of porcine cardiovascular tissues.

Collagen from the cardiovascular system is extremely resistant to proteolytic digestion, in contrast with the proteoglycans of these connective tissues. In particular this is true for the heart valves, which contain the largest proportion of collagen. The tensile strength of aortic tissue incubated at 37 degrees C declines rapidly unless fixed with aldehydes. Stabilized glutaraldehyde gives rise to the most stable form of cross-link and renders the tissue structurally intact after more than 4 years of incubation at 37 degrees C in physiological solution. Formaldehyde, on the other hand, gives rise to transcient cross-links.

Animals↗
PubMed1978

Nearest-neighbor interactions of the major RNA tumor virus glycoprotein on murine cell surfaces.

Formaldehyde-fixed Staphylococcus aureus and monospecific antiserum to gp70, the major envelope glycoprotein of murine leukemia virus, were used to immunoadsorb gp70 from Nonidet P40 extracts prepared from surface-radioiodinated murine cells. The labeled gp70 molecules in these cells were linked to a protein of approximately 15,000 daltons via native disulfide bonding. Prior treatment of cells with the reversible, bifunctional, crosslinking reagent dimethyl-3,3'-dithiobispropionimidate, followed by immunoadsorption and two-dimensional diagonal electrophoresis, revealed apparent homodimers and homotrimers of the 85,000-dalton complex. Identical treatment of purified type C RNA tumor virus from murine cells also revealed homodimeric and homotrimeric species, demonstrating similar self-associating tendencies of this glycoprotein in both intact virus and the plasma membrane of nonproducing murine cells. One cross-linked product consistently detected on the surfaces of murine cells was not present after crosslinking of a representative strain of murine leukemia virus.

Cells, Cultured↗
PubMed1978

Two-step modification of aspartate aminotransferase with 1,5-difluoro-2,4-dinitrobenzene. Cross-link localization.

At pH 7, the apoenzyme of carboxymethylated and acylated aspartate aminotransferase reacts selectively with 1,5-difluoro-2,4-dinitrobenzene to form a single intramolecular covalent bond with the epsilon-amino group of the functional lysine residue located within the active centre. On shifting the pH to 9, the second fluorine atom of the bifunctional reagent is substituted with the sterically adjacent side groups of cysteine and tyrosine residues. The modified apoenzyme was subjected to partial proteolysis with pronase, and the digest was used to obtain and isolate the labeled products and to localize amino acid residues involved in the reaction. The established structures of several peptides containing Cys-2,4-dinitrobenzene-Lys and Tyr-2,4-dinitrobenzene-Lys allowed the identification of the amino acid residues involved in the reaction with the bifunctional reagent as Lys 258, Cys 390 and probably Tyr-70. The residues of Cys and Tyr are thus located at a distance of approximately 5 A (the length of the dinitrophenylene bridge) from the lysine residue forming an aldimine bond with pyridoxal 5'-phosphate in the active site.

Animals↗
PubMed1992

In vitro phosphorylation of the erythropoietin receptor and an associated protein, pp130.

The cytoplasmic domain of the cloned erythropoietin (EPO) receptor (EPOR) contains no protein kinase motif, yet addition of EPO to EPO-responsive cells causes an increase in protein-tyrosine phosphorylation. Here we show that addition of EPO or interleukin-3 (IL-3) to an IL-3-dependent cell line expressing the wild-type EPOR causes a small fraction (less than 5%) of total cellular EPOR to shift in gel mobility from 66 to 72 kDa, due at least in part to phosphorylation. Using biotinylated EPO as an affinity reagent, we show that the 72-kDa species is greatly enriched on the cell surface. To demonstrate that a protein kinase activity associates with cell surface EPOR, cells were incubated with biotinylated EPO and then cross-linked with a thiol-cleavable chemical cross-linker. The avidin-agarose-selected complexes were incubated with [gamma-32P]ATP. After in vitro phosphorylation and denaturation without reducing agent, both antiphosphotyrosine and anti-EPOR antibodies immunoprecipitated labeled 72-kDa EPOR and an unidentified 130-kDa phosphoprotein (pp130), indicating that a protein kinase is associated with cell surface EPOR and that a fraction of the EPOR was phosphorylated on tyrosine residues either in the cells or during the cell-free phosphorylation reaction. Under reducing conditions, the 72-kDa phosphorylated EPOR but not pp130 was immunoprecipitated with an anti-EPOR antibody, suggesting that the pp130 is bound to the EPOR by the thiol-cleavable chemical cross-linker. Previously, we showed that deletion of the 42 carboxy-terminal amino acids of the EPOR allows cells to grow in 1/10 the normal EPO concentration, without affecting receptor number or affinity. Two carboxy-terminal truncated EPO receptors that are hyperresponsive to EPO were poorly phosphorylated during the in vitro reaction, suggesting that the carboxy-terminal region of the EPOR contains a site for phosphorylation or a site for interaction with a protein kinase. Our data suggests that phosphorylation or interaction with a protein kinase in the carboxy-terminal region may down-modulate the proliferative action of the EPOR.

Amino Acid Sequence↗
PubMed1977

Nearest neighbor relationships of the polypeptides in ubiquinone cytochrome c reductase (complex III).

Ubiquinone cytochrome c reductase (complex III) in detergent dispersion has been cross-linked with two reversible cross-linking agents dithiobissuccinimidylpropionate and dimethyl-3.3'-dithiobispropionimidate and the cross-linked products formed have been analyzed by two-dimensional gel electrophoresis. Under mild reaction conditions, polypeptides I and II, II and VI, I and V, and VI and VII were the most prominent subunit pairs seen. With higher levels of reagent, larger aggregates were produced until an aggregate of apparent molecular weight 310 000 was the dominant band on gels. This is the complex III monomer.

Cytochrome Reductases↗
PubMed1977

Localization of reducing group activity in the structural protein ribbons of the egg capsule of the gastropod mollusc Buccinum undatum L.

Egg capsules of the gastropod molluse Buccinum undatum L. show a staining reaction with silver-methenamine reagent with prior treatment with periodate. The reactivity is specifically localized on the striated structural protein ribbons which form the capsule walls. The staining is in the region of ribbon most resistant to chemical degradation and where the constituent protein monomers are believed to overlap and be cross-linked. Since the proteins contain little cysteine it is likely that the staining originates in aldehyde groups. Staining is abolished by borohydride reduction. It is suggested that the aldehyde groups are a locus of stabilization and cross-linking since previous work has also shown association of an aldehyde secretion with hardening of the capsules.

Aldehydes↗
PubMed1979

The reactions of Escherichia coli citrate synthase with the sulfhydryl reagents 5,5'-dithiobis-(2-nitrobenzoic acid) and 4,4'-dithiodipyridine.

Citrate synthase of Escherichia coli reacts rapidly with 1 equivalent of Ellman's reagent, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), per subunit, losing completely its sensitivity to the allosteric inhibitor, NADH. When the enzyme is treated instead with 4,4'-dithiodipyridine (4,4'-PDS), all activity is lost. Certain evidence in this paper is consistent with the belief that the sulfhydryl group modified by DTNB, and that whose modification by 4,4'-PDS inactivates the enzyme, are the same. (i) Both reagents abolish NADH fluorescence enhancement by the enzyme. (ii) Saturating levels of NADH and some other adenylic acid derivatives inhibit the reactions with both reagents. (iii) When the enzyme is modified with one equivalent of DTNB or 4,4'-PDS, subsequent reactivity toward the other reagent is greatly decreased. (iv) Following modifications, the DTNB and 4,4'-PDS derivatives spontaneously lose thionitrobenzoate (TNB) or pyridine-4-thione (PT), respectively, in reactions which are thought to involve displacement of TNB or PT by a second enzyme sulfhydryl group, so that an enzyme disulfide is introduced. The introduction of the disulfide bond, if this is what occurs, does not lead to cross-linking of citrate synthase polypeptide chains, as judged by sodium dodecyl sulfate polyacrylamide gel electrophoresis under nonreducing conditions. Certain evidence has also been found, however, that the sites of modification by DTNB and 4,4'-PDS are not the same. (i) DTNB modification desensitizes to NADH but does not inactivate, while 4,4'-PDS inactivates at least 99.9%. (ii) The presumed disulfide from elimination of TNB is also active, while that from PT modification is no more active than the original 4,4'-PDS modified product. (iii) Prior modification of the enzyme with DTNB affords no protection against later inactivation by 4,4'-PDS. The studies therefore indicate a close relationship between the DTNB desensitization and 4,4'-PDS inactivation, but they are unable to identify it exactly. Other properties of the DTNB reaction are also described, and a hypothesis is offered to explain quantitatively the finding that desensitization lags behind modification during the modification of citrate synthase by DTNB.

Binding Sites↗
PubMed1979

Structure of cross-linked rabbit muscle phosphofructokinase in solution.

Cross-linked rabbit muscle phosphofructokinase in the active tetrameric and octameric state was studied in solution by hydrodynamic methods and small angle x-ray scattering techniques. The translational diffusion coefficients were determined by means of inelastic light scattering and were found to be 3.60 (+/- 0.02) x 10(-7) cm2 . s-1 for the tetramer and 2.54 (+/- 0.15) x 10(-7) cm2 . s-1 for the octamer. From small angle x-ray scattering measurements the radius of gyration, the specific inner surface area, and the volume were determined for both enzyme forms, revealing that the octameric cross-linked form is approximately spherical, with a diameter of 120.0 A, whereas the tetrameric form is asymmetric having an axial ratio of 2. By comparison of the scattering curves with triaxial geometric bodies which are equivalent in scattering, the tetrameric enzyme is described as a rectangular prism, with overall dimensions of A = 131.0 A, B = 131.0 A, and C = 65.0 A, and the octameric form as that of a cube with A = B = C = 120.0 A. The shape of the protomer, having a radius of gyration of 24.8 A, in the tetramer and octamer is similar to that for the native tetramer at pH 10 in the presence of 5 mM fructose 6-phosphate or 15 mM fructose 1,6-bis-phosphate. From the different shapes of the scattering curves of the native phosphofructokinase at pH 7.5 in the presence of 15 mM ATP and of the cross-linked tetramer or octamer, it can be inferred that the shapes of the protomers are different: in the presence of ATP the protomers are elongated, having an axial ratio of 1.8 to 2.0; the cross-linked state reveals a spherical protomer of radius 33.0 A, similar to that of the native enzyme at pH 7.5 in the presence of fructose 6-phosphate or fructose 1,6-bisphosphate.

Animals↗
PubMed1978

Functional consequences of tryptophan modification in human fibrinogen.

When human fibrinogen was modified with H2O2, inter- and intra-molecular cross-links of fibrinogen were formed, accompanied with oxidation of tryptophan, methionine and tyrosine residues. These cross-links may be closely associated with oxidation of tryptophan residues. The polymerization activity of fibrinogen with thrombin was decreased markedly by this modification. Modification of tryptophan residues in fibrinogen was also performed with 2-hydroxy-5-nitrobenzyl bromide. Modification of two out of a total 78 tryptophan residues in the molecule with the reagent led to the intensification (1.7 times) of the polymerization activity with thrombin and further modification of the next two residues led to complete loss of the polymerization activity. The first two tryptophan residues to be modified are in Fragment D, and the next two occur in Fragment E.

2-Hydroxy-5-nitrobenzyl Bromide↗
PubMed1977

Synthesis and characterization of new psoralen derivatives with superior photoreactivity with DNA and RNA.

The synthesis of five new psoralen derivatives is described. Three of these, 4'-hydroxymethyl-4,5',8-trimethylpsoralen, 4'-methoxymethyl-4,5',8-trimethylpsoralen, and 4'-aminomethyl-4,5',8-trimethylpsoralen hydrochloride, and characterized with respect to their photoreactivity with DNA and RNA. They are found to be greatly superior to 4,5',8-trimethylpsoralen and 8-methoxypsoralen, the two commonly used psoralens, in their abilities to saturate the photoreactive sites on DNA and RNA without repeated addition of reagent. A simplified mechanism for the photoreaction of psoralens with nucleic acids is presented and provides a basis for understanding the superior properties of these compounds. The compounds have superior reactivity not only with isolated DNA and RNA but also in viruses and in cells. Psoralens are shown for the first time to cross-link RNA double helices.

Binding Sites↗
PubMed1976

The role of 16S rRNA in ribosomal binding of IF-3.

The binding of initiation factor IF-3 to Escherichia coli 30S ribosomal subunits has been found to be inhibited by rRNA ligands such as ethidium bromide, polyamines, and monovalent alkali metals. The order of effectiveness of the polyamines (spermine greater than spermidine greater than putrescine) and alkali metals (Li+ greater than Na+ greater than K+) in inhibiting the ribosomal binding of IF-3 parallels their degree of affinity for the RNA. Furthermore, the binding of IF-3 to 30S subunits chemically modified by photooxidation with rose bengal, nitration with tetranitromethane, and reaction with kethoxal, monoperphthalic acid, and p-chloromercuribenzoic acid was studied. Results obtained after the direct treatment of the 30S subunits with the above chemical reagents or upon reconstitution of 30S particles having a modified rRNA or ribosomal proteins indicate that the IF-3 binding site is preferentially lost when the rRNA becomes modified. It was found that IF-3 could bind normally to 30S subunits lacking protein S1 or proteins S11, S12, S19, and S21 (and perhaps S14) which had been cross-linked to IF-3 in other laboratories.

Bacterial Proteins↗
PubMed1978

The effects of deoxycholate and trypsin on the cross-linking of rabbit skeletal muscle sarcoplasmic reticulum proteins.

Dithiobis (succinimidyl propionate) has been used to cross-link sarcoplasmic reticulum microsome proteins. Although the 100,000 dalton calcium stimulated ATPase and the 60,000 dalton calcium-binding protein calsequestrin were readily cross-linked to form homopolymers, no heteropolymer formation between these two proteins were detected. The 90,000 dalton protein A1 which is always observed in our preparations appeared to preferrentially form dimers on cross-linking. When calsequestrin was solubilized using 0.1 mg deoxycholate/mg protein, this protein was not cross-linked even at dithiobis(succinimidyl propionate) concentrations ten times those used to cross-link this protein in the intact membrane. In a similar manner the deoxycholate-solubilized ATPase (0.5 mg deoxycholate/mg protein) was not cross-linked by dithiobis (succinimidyl propionate). These results suggest that the state of aggregation of the sarcoplasmic reticulum proteins may be modified when solubilized in detergents such as deoxycholate. When the 100,000 dalton ATPase polypeptide was cleaved with trypsin to two fragments with molecular weights of approximately 55,000, these could be readily cross-linked. The fragments were capable of forming polymers with either other 55,000 dalton fragments or with the 100,000 dalton ATPase. The 29,000 and 22,000 dalton fragments, produced by further tryptic cleavage of the 55,000 dalton fragments, were not cross-linked at dithiobis (succinimidyl propionate) concentrations which readily cross-linked the 55,000 dalton fragments. Thus tryptic cleavage of the ATPase to fragments smaller than 55,000 dalton altered associations made by the ATPase in the membrane.

Adenosine Triphosphatases↗
PubMed1977

Investigations on the binding sites of the basement membrane zone for pemphigoid antibodies in vitro. II. Immunohistochemical reactions of the reactive groups.

In continuing our studies on the characteristics of the antigenic structures of the basement membrane, procedures used in histochemistry for the identification and blocking of reactive groups have been adapted in this present work to the pretreatment of cryostat sections of guinea-pig tongue. These sections have then been studied by the indirect immunofluorescence method. By means or reagents, which produce a reversible extinction of the basement membrane fluorescence produced with pemphigoid sera, it proved possible to determine the existence of certain chemical groupings which bind the anti-basement membrane antibodies, namely: free carboxyl groups deriving from amino acids, hydrogen bridges in which the hydroxyl groups from the carbohydrates in the antigen are probably involved, bonds involving the free aldehydes of the antigen (either cross-links from aldehydes, or formation of Schiff's bases with amino groups of the antibodies), and lastly, to a lesser extent, disulphide bonds. The antigen/antibody reaction probably occurs in the neighbourhood of the alpha-glucosido-beta-galactosido-hydroxylysine. A reaction model has been developed from these findings. There were also some indications that the antigenic structures of the intercellular substance are chemically related to those of the basement membrane. The cell nucleus antigens, on the other hand, appear to possess different chemical properties.

Animals↗
PubMed1978

The denaturation of covalently inhibited swine pepsin.

Studies are reported on the denaturation of freshly prepared, intact swine pepsin, which was inactivated by reaction with diazoacetylglycine ethyl ester, to prevent autolysis. Denaturation about pH 6 was found to involve a small expansion of the molecular domain with some loss of organized secondary structure. On the other hand, increasing concentrations of guanidine hydrochloride induced cooperative transitions in both the native and alkali denatured forms to give a cross-linked random coil. No conditions could be found in which these reactions were reversible. Removal of denaturing conditions usually resulted in aggregation and precipitation of protein. From these studies, it would seem that the active conformation is largely predetermined in the zymogen.

Animals↗