| 1. |
- Dahlqvist-Edberg, Ulla, et al.
(författare)
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The demonstration in rat liver cell sap of protein kinase and phosphoprotein phosphatase active on fructose-bisphosphatase
- 1982
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - : Elsevier BV. - 0167-4838 .- 1879-2588. ; 706:2, s. 239-244
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Tidskriftsartikel (refereegranskat)abstract
- A protein kinase active on fructose-bisphosphatase (D-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11) was demonstrated in rat liver cell sap. The protein kinase activity was stimulated by cyclic AMP and coincided with the activity of cyclic AMP-dependent protein kinase type I. In addition, three different peaks of phosphoprotein phosphatase active on [32P] phosphofructose-bisphosphatase were found on chromatography of rat liver cell sap on a DEAE-cellulose column. These phosphatases needed divalent cations for full activity. 5'-AMP, a negative modulator of fructose-bisphosphatase, had no effect on the phosphorylation-de-phosphorylation reactions of the enzyme. ATP and Ca2+ did not influence the dephosphorylation reaction of fructose-bisphosphatase.
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| 2. |
- Henriksson, Gunnar, et al.
(författare)
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Is cellobiose dehydrogenase from Phanerochaete chrysosporium a lignin degrading enzyme?
- 2000
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - 0167-4838 .- 1879-2588. ; 1480:02-jan, s. 83-91
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Tidskriftsartikel (refereegranskat)abstract
- Cellobiose dehydrogenase (CDH) is an extracellular redox enzyme of ping-pong type, i.e. it has separate oxidative and reductive half reactions. Several wood degrading fungi produce CDH, but the biological function of the enzyme is not known with certainty. It can, however, indirectly generate hydroxyl radicals by reducing Fe3+ to Fe2+ and O-2 to H2O2. Hydroxyl radicals are then generated by a Fenton type reaction and they can react with various wood compounds, including lignin. In this work we study the effect of CDH on a non-phenolic lignin model compound (3,4-dimethoxyphenyl glycol). The results indicate that CDH can affect lignins in three important ways. (1) It breaks beta-ethers; (2) it demethoxylates aromatic structures in lignins; (3) it introduces hydroxyl groups in non-phenolic lignins. The gamma-irradiated model compound gave a similar pattern of products as the CDH treated model compound? when the samples were analyzed by HPLC, suggesting that hydroxyl radicals are the active component of the CDH system.
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| 3. |
- MARTINELLE, M, et al.
(författare)
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KINETICS OF ACYL TRANSFER-REACTIONS IN ORGANIC MEDIA CATALYZED BY CANDIDA-ANTARCTICA LIPASE-B
- 1995
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - ROYAL INST TECHNOL,DEPT BIOCHEM & BIOTECHNOL,S-10044 STOCKHOLM,SWEDEN. : ELSEVIER SCIENCE BV. - 0167-4838 .- 1879-2588. ; 1251:2, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- The acyl transfer reactions catalysed by Candida antarctica lipase B in organic media followed a bi-bi ping-pong mechanism, with competitive substrate inhibition by the alcohols used as acyl accepters. The effect of organic solvents on V-m and K-m was investigated. The V-m values in acetonitrile was 40-50% of those in heptane. High K-m values in acetonitrile compared to those in heptane could partly be explained by an increased solvation of the substrates in acetonitrile. Substrate solvation caused a 10-fold change in substrate going from heptane to acetonitrile. Deacylation was the rate determining specificity, defined as (V-m/K-m)(ethyl) (octanoate)/(V-m/K-m)(octanoic) (acid), step for the acyl transfer in heptane with vinyl- and ethyl octanoate as acyl donors and (R)-2-octanol as acyl acceptor. With I-octanol, a rate determining deacylation step in heptane was indicated using the same acyl donors. Using I-octanol as acceptor in heptane, S-ethyl thiooctanoate had a 25- to 30-fold lower V-m/K-m value and vinyl octanoate a 4-fold higher V-m/K-m value than that for ethyl octanoate. The difference showed to be a K-m effect for vinyl octanoate and mainly a K-m effect for S-ethyl thiooctanoate. The V-m values of the esterification of octanoic acid with different alcohols was 10-30-times lower than those for the corresponding transesterification of ethyl octanoate. The low activity could be explained by a low pH around the enzyme caused by the acid or a withdrawing of active enzyme by nonproductive binding by the acid.
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| 4. |
- Ottosson, Jenny, et al.
(författare)
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Size as a parameter for solvent effects on Candida antarctica lipase B enantioselectivity
- 2002
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - 0167-4838 .- 1879-2588. ; 1594:2, s. 325-334
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Tidskriftsartikel (refereegranskat)abstract
- Changes in solvent type were shown to yield significant improvement of enzyme enantioselectivity. The resolution of 3-methyl-2-butanol catalyzed by Candida antarctica lipase B, CALB, was studied in eight liquid organic solvents and supercritical carbon dioxide, SCCO2. Studies of the temperature dependence of the enantiomeric ratio allowed determination of the enthalpic (Delta(R-S)Delta H-double dagger) as well as the entropic (Delta(R-S)Delta S-double dagger) contribution to the overall enantioselectivity (Delta(R-S)Delta G(double dagger) = -RTlnE). A correlation of the enantiomeric ratio, E. to the van der Waals volume of the solvent molecules was observed and suggested as one of the parameters that govern solvent effects on enzyme catalysis. An enthalpy-entropy compensation relationship was indicated between the studied liquid solvents. The enzymatic mechanism must be of a somewhat different nature in SCCO2, as this reaction in this medium did not follow the enthalpy-entropy compensation relation.
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| 5. |
- Paul, Jan, et al.
(författare)
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Fast heme release from inactive proteins
- 1991
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - 0167-4838 .- 1879-2588. ; 1079:3, s. 330-334
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Tidskriftsartikel (refereegranskat)abstract
- Kinetics for the release of the prosthetic group from hemoproteins is presented. Heme-protein separation is a biphasic reaction, where an initial phase is significantly faster than the dominant, slow phase. A previous communication concluded that the slow phase represents the active protein. This communication presents data for porphyrin release which shows that the initial fast phase represents an inactive form of the protein. Moreover, we suggest that the fast to slow phase ratio is a sensitive monitor of sample quality for many hemoproteins and that an extrapolation of the slow phase absorbance leads to new estimates for the true physical parameters of unperturbed proteins.
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| 6. |
- Paul, Jan, et al.
(författare)
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Spin and electron distributions in heme-cyanide models and hemeproteins
- 1985
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - : Elsevier BV. - 0167-4838 .- 1879-2588. ; 832:3, s. 265-273
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Tidskriftsartikel (refereegranskat)abstract
- Proton NMR spectra of low-spin Fe(III) cyanoprotoheme as prosthetic group in a number of proteins are presented. The diagonally positioned 1-, 5- and 3-, 8-methyl groups obey shifts proportional to the Fe(III)/(II) reduction potential Em7, which indicates a pseudo-contact interaction. The correlation with Em7 is understandable if one postulates an enhanced rhombic distortion, dominating the Fe-methyl dipolar interactions. Hatree-Fock-Slater quantum chemical calculations show no significant changes of spin density as a function of the Fe-L5 distance, except at the iron atom and predominantly in the 3dxz and 3dyz orbitals. 4p orbitals, on the other hand, uphold most of the changes of electron density. We also observe a principal difference in the amino acid sequences in the heme-accommodating pocket of oxygen carriers and two-electron transmitters.
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| 7. |
- Paul, Jan, et al.
(författare)
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The vibrational bands of carbon monoxide bound to hemes or metal surfaces
- 1985
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - : Elsevier BV. - 0167-4838 .- 1879-2588. ; 832:3, s. 257-264
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Tidskriftsartikel (refereegranskat)abstract
- Infrared spectra of imidazole carbonyl complexes of 2,4-substituted hemes are presented. An increased CO stretch frequency is accompanied by a lowered FeC vibrational energy. Hartree-Fock-Slater electron structure calculations discern π and σ contributions to the observed shifts of vibrational energies. We conclude that an enhanced electron availability manifests itself as (i) a lowered ferric/ferrous reduction potential, (ii) increased filling of the 2π orbital of liganded CO which in turn reduces νCO and increases νFec, and (iii) increased basicity of the liganded CO. Analogies between CO liganded to heme and CO adsorbed onto metal surfaces are discussed.
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| 8. |
- Persson, Bengt L., et al.
(författare)
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NBD-Cl modification of essential residues in mitochondrial nicotinamide nucleotide transhydrogenase from beef heart
- 1988
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - : Elsevier BV. - 0167-4838 .- 1879-2588. ; 953, s. 241-248
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Tidskriftsartikel (refereegranskat)abstract
- Modification of mitochondrial nicotinamide nucleotide transhydrogenase (NADPH:NAD+ oxidoreductase, EC 1.6.1.1) with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl), followed by measurement of the absorption or fluorescence of the transhydrogenase-NBD adducts, resulted in a biphasic labelling of approx. 4–6 sulfhydryls, presumably cysteine residues. Of these 1–2 (27%) were fast-reacting and 3–4 (73%) slow-reacting sulfhydryls. In the presence of substrates, e.g., NADPH, the labelling was monophasic and all sulfhydryls were fast-reacting, suggesting that the modified sulfhydryls are predominantly localized peripheral to the NAD(P)(H)-binding sites. The rates of modification allowed the calculation of the rate constants for each phase of the labelling. Both in the absence and in the presence of a substrate, e.g., NADPH, the extent of labelling essentially parallelled the inhibition of transhydrogenase activity. Attempts to reactivate transhydrogenase by reduction of labelled sulfhydryls were not successful. Photo-induced transfer of the NBD adduct in partially inhibited transhydrogenase, from the sulfhydryls to reactive NH2 groups of amino-acid residue(s), identified as lysine residue(s), was parallelled by an inhibition of the residual transhydrogenase activity. It is suggested that a lysine localized close to the fast-reacting NBD-Cl-reactive sulfhydryl groups is essential for activity.
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| 9. |
- Kleczkowski, Leszek A, 1954-
(författare)
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Is leaf ADP-glucose pyrophosphorylase an allosteric enzyme?
- 2000
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - 0167-4838 .- 1879-2588. ; 1476:1, s. 103-108
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Tidskriftsartikel (refereegranskat)abstract
- Barley leaf ADP-glucose pyrophosphorylase (AGPase), a key enzyme of starch synthesis in the chloroplast stroma, was analysed, in both directions of the reaction, with respect to details of its regulation by 3-phosphoglycerate (PGA) and inorganic phosphate (Pi) which serve as activator and inhibitor, respectively. AGPase was found to catalyse a close-to-equilibrium reaction, with the K-eq value of approximately 0.5, i.e. slightly favouring the pyrophosphorolytic direction. When the enzyme was analysed by substrate kinetics, PGA acted either as a linear (hyperbolic response) 'non-competitive' activator (forward reaction) or a linear near-'competitive' activator (reverse reaction). When the activation and inhibition patterns with PGA and Pi, respectively, were studied in detail by Dixon plots, the response curves to effecters also followed hyperbolic kinetics, with the experimentally determined K-a and K-i values on the order of micromolar. The results suggest that the regulation of AGPase proceeds via a non-cooperative mechanism, where neither of the effecters, when considered separately, induces any allosteric response. The evidence, discussed in terms of an overall kinetic mechanism/regulation of leaf AGPase, prompts caution in classifying the protein as an 'allosteric enzyme'. (C) 2000 Elsevier Science B.V. All rights reserved.
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| 10. |
- Adlercreutz, Patrick
(författare)
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Activation of enzymes in organic media at low water activity by polyols and saccharides
- 1993
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Ingår i: BBA - Protein Structure and Molecular Enzymology. - 0167-4838. ; 1163:2, s. 144-148
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Tidskriftsartikel (refereegranskat)abstract
- Horse liver alcohol dehydrogenase and α-chymotrypsin were deposited on a porous support material, Celite. After equilibration at a well-defined water activity, the catalytic activity was measured with diisopropyl ether as reaction medium. The effects of the presence of polyols and simple saccharides in the preparations were investigated. The additives caused a considerable increase in the amount of water bound to the preparation at a fixed water activity. At low water activities the catalytic activity was increased and at high water activity it was decreased by the additives. The presence of additives increased the ratio of alcoholysis-to-hydrolysis activity of chymotrypsin.
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