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We have investigated the interaction between calcium ions and erythrocyte transglutaminase and the enzyme activation. The binding involves both high and low affinity sites, but only the former ones are relevant for activation. The binding of calcium and the activation are modified by treatment with NBD-Cl and with PLP suggesting the presence of cysteine and lysine residues at the high affinity binding sites. The interaction of the enzyme with calcium is not calmodulin dependent and is easily detected as a shift in electrophoretic mobility in the presence of SDS. 相似文献
4.
Addition of low concentrations of acrylamide to the assay mixture of erythrocyte transglutaminase leads to a strong inhibition of the enzyme with a mechanism consistent with a non-competitive inhibition against both substrates. For the quenching of the intrinsic fluorescence of the protein, much higher concentrations of acrylamide are required so that both phenomena appear independent of each other. In this particular case, therefore, acrylamide can be employed to obtain information on ligand-triggered conformational changes. 相似文献
5.
Glycogen synthetase from skeletal muscle is rapidly inactivated by DEPC. In the presence of the substrate UDPG only 50% of the enzyme activity is lost. The concomitant addition of both UDPG and the allosteric activator glucose-6-phosphate almost completely prevents the inactivation by DEPC. Since glucose-6-phosphate alone does not prevent the inactivation by DEPC, it is concluded that it is effective through a potentiation of the effects of UDPG, possibly through a conformational change of the enzyme. 相似文献
6.
C M Bergamini M Signorini C Ferrari F Dallocchio 《Archives of biochemistry and biophysics》1983,227(2):397-405
The kinetic properties of rabbit muscle uridine diphosphoglucose (UDP-Glc) pyrophosphorylase have been studied, in both directions, with respect to substrate saturation, product inhibition, and cation requirement for activity. The results demonstrate that UDP-Glc pyrophosphorylase is a non-Michaelian enzyme: the synthetic reaction is characterized by a marked inhibition by glucose-1-phosphate (at concentrations higher than 0.3 mM) and by an hyperbolic saturation for UTP. In the reverse reaction, instead, the saturation function for UDP-Glc is hyperbolic and that for inorganic pyrophosphate is sigmoid, with a high Hill coefficient of (nH) 2.5. The study of the metal requirement indicates a distinctive ability of cations to stimulate the reactions of synthesis and degradation of the sugar nucleotide and a different stoichiometry of the metal chelates involved. The reaction mechanism is of the ordered-sequential type and the data of product inhibition allowed the identification of glucose-1-phosphate as the first substrate bound and UDP-Glc as the last product released. The inhibition pattern by UDP-Glc gives evidence for cooperativity also in the binding of this molecule. 相似文献
7.
Pollination Ecophysiology of Mercurialis annua L. (Euphorbiaceae), an Anemophilous Species Flowering all Year Round 总被引:1,自引:0,他引:1
Mercurialis annua L. is a dioecious anemophilous species thatflowers all year round in central and southern Italy. The flowersof both sexes are dimorphic: the female flower has a vestigialcalyx; the male flower consists only of a calyx that opens atanthesis. The anthers always dehisce after anthesis. The anthesisof male flowers seems to be temperature dependent, whereas antherdehiscence is related to relative humidity. The pollen grainsvary in volume according to the season: they are smaller whenrelative humidity is low and vice versa. They always decreasein volume after anther dehiscence and have the capacity to varyin volume and reach equilibrium with a changing environment.Viability is high, but may drop suddenly during heavy rain orhail that damage the exposed male flowers. The number of pollengrains per stigma varies from 0 to 300. The data is discussedin relation to the type of pollination and environmental characteristics.Copyright1994, 1999 Academic Press Mercurialis annua, dioecism, anthesis, anther dehiscence, pollen volume, pollen viability, anemophilous pollination, pollination ecology 相似文献
8.
Vittorio Moretto Fernando Formaggio Marco Crisma Gian Maria Bonora Claudio Toniolo Ettore Benedetti Antonello Santini Michele Saviano Benedetto Di Blasio Carlo Pedone 《Journal of peptide science》1996,2(1):14-27
A complete series of terminally blocked, monodispersed homo-oligopeptides (to the pentamer level) from the sterically demanding, medium-ring alicyclic Cα,α-disubstituted glycine 1-aminocyclooctane-1-carb oxylic acid (Ac8c), and two Ala/Ac8c tripeptides, were synthesized by solution methods and fully characterized. The preferred conformation of all the oligopeptides was determined in deuterochloroform solution by IR absorption and 1H-NMR. The molecular structures of the amino acid derivative Z-Ac8c-OH, the dipeptide pBrBz- (Ac8c)2-OH and the tripeptide pBrBz-(Ac8c)3-OtBu were assessed in the crystal state by X-ray diffraction. Conformational energy computations were performed on the monopeptide Ac-Ac8c-NHMe. Taken together, the results obtained strongly support the view that the Ac8c residue is an effective β-turn and helix former. A comparison is also made with the conformational preferences of α-aminoisobutyric acid, the prototype of Cα, α-disubstituted glycines, and of the other members of the family of 1-aminocycloalkane-1-carboxylic acids (Acnc, with n=3, 5–7) investigated so far. The implications for the use of the Ac8c residue in peptide conformational design are considered. 相似文献
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Ettore Benedetti Benedetto Di Blasio Vincenzo Pavone Carlo Pedone Claudio Toniolo Gian Maria Bonora 《International journal of biological macromolecules》1980,2(4):217-224
The X-ray diffraction and i.r. absorption conformational analysis of has showed the absence of intramolecularly hydrogen-bonded peptide conformations in the solid state. The molecules are held together in rows of ‘cyclic dimer’ motifs through intermolecular NH … OC (acid) and OH … OC {urethane} hydrogen bonds, the secondary amide-like group of the urethane moiety being in the unusual cis conformation, whereas the carboxylic acid group in the common syn conformation. The two molecules in the unit cell present a centrosymmetric set of ?, ψ1, and ψ2 values. In polar solvents solvated species largely predominate. In saturated hydrocarbon solution non-associated and associated (mostly involving the carboxylic acid CO as the proton acceptor) species simultaneously occur. The extent of association decreases with dilution. The amount of intramolecularly hydrogen-bonded oxy-C7 and C5 forms if any, should be extremely small. The type of association at saturation seems to differ from that found in the crystalline compound obtained by precipitation with saturated aliphatic hydrocarbons (from a diethyl ether solution). 相似文献