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H Sund

Publications and source records attributed to H Sund.

At least 19 recordsLinked to original sources
PubMed1986

Demonstration of glutamate dehydrogenase isozymes in beef heart mitochondria.

Glutamate dehydrogenase (GDH) has been purified from beef heart mitochondria and compared with crystalline beef liver GDH. The specific activity of heart GDH was 127 units and of liver GDH 80 units. Heart GDH subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis had a protein corresponding to liver GDH and a smaller molecular weight protein. On agarose gel electrophoresis heart GDH activity was resolved into two fractions (with or without protease inhibitors) while liver had only one fraction. One of the heart fractions moved with liver GDH on electrophoresis. Thermal stability studies showed heart and liver GDH activity differed. Mouse antibodies to liver GDH precipitated both liver and heart GDH on double immunodiffusion. Mouse antibodies to liver GDH identified on nitrocellulose paper the polypeptide band of liver and heart GDH that were the same molecular weight but did not cross-react with the smaller molecular weight polypeptide present in heart GDH. Trypsin digestion of the two major protein bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified GDH from beef heart mitochondria did not show any overlapping peptides. We conclude beef heart GDH activity is composed of two isozymes. One is the same as beef liver GDH, and the other is a smaller molecular weight protein. We propose the terms GDH-LM for the liver GDH isozyme and GDH-HM for the smaller molecular weight isozyme present in heart mitochondria but not liver.

Animals↗
PubMed1985

Optical properties and structure of tetrapyrroles. A report of a symposium held at the University of Konstanz, FRG, August 12-17, 1984.

Many basic life processes such as oxygen transport, electron transport, photosynthesis and plant development, are mediated by tetrapyrroles. It has long been recognized that optical and other physicochemical properties of tetrapyrroles are highly important not only for characterization of the various relevant systems but also to provide a key role in the understanding of their structural and functional aspects. The symposium described below was devoted mainly to recent advances in the optical and molecular properties of biologically important systems, involving both cyclic and open-chain tetrapyrroles. The topics presented and discussed ranged from physics and chemistry to plant biology and medicine. This interdisciplinary character of the meeting conforms with previous symposia also held in Konstanz: Protein-Ligand Interactions (1974) and Transport by Proteins (1978) [see FEBS Lett. (1975) 54, 1-4, and FEBS Lett. (1979) 103, 1-4]. In order to stimulate exchange of ideas, new experimental approaches and techniques, emphasis was placed on the discussions following each presentation, reports of which are also included in the book published. Preprints of the papers presented were distributed some time prior to the symposium. The symposium was mainly supported by the Stiftung Volkswagenwerk and the University of Konstanz. The meeting was based on 29 invited lectures which were divided into four sections.

Animals↗
PubMed1982

Membrane-associated nucleotide pyrophosphatase activity on leucocytes from different compartments.

The distribution of membrane-associated nucleotide pyrophosphatase activity has been investigated on mouse leucocytes of different origin. It is shown that enzyme-specific activity is higher on bone-marrow cells than on cells derived from peripheral organs. Since thymus lymphocytes show the lowest activity, it is obvious that the thymus environment can influence the enzyme activity on bone-marrow stem cells which have entered this organ. Spleen cells from thymus-deficient nude mice displayed more enzyme activity than spleen cells from normal mice, although the percentage of lymphocytes was similar in both donor-cell populations.

Animals↗
PubMed1977

Studies of glutamate dehydrogenase. Analysis of quaternary structure and contact areas between the polypeptide chains.

Cross-linking of the unimer of glutamate dehydrogenase from beef liver (consisting of six polypeptide chains each having a molecular weight of 56000) with dimethyladipimidate and subsequent analysis by sodium dodecylsulfate electrophoresis shows predominantly the trimeric species (molecular weight 168000). Treatment with dimethylimidates of other chain length yields significantly less trimeric species indicating that the amino groups being cross-linked are within a distance of about 0.85 nm. Comparison of the molar amount of incorporated [14C]dimethyladipimidate with the number of modified amino groups (determined with trinitrobenzenesulfonic acid) shows that although 8-9 of the 34 amino groups have reacted, only 2-3 of them are involved in cross-links. Reaction with dimethylimidates inactivates the enzyme. The loss of the activity is partly concomitant to cross-linking to the trimeric species and not simply due to the modification of essential lysine residues. This is supported by the fact that, although more lysine residues react with mono-functional methylimidates, the loss of activity is reduced. Purified chymotryptic and tryptic peptides of the radioactive-labeled trimeric species were subjected to sequence analysis. Six peptides containing 75% of the total label were identified: one involves the amino-terminal residue alanine-1 and the others involve lysine-105, lysine-154, lysine-269, lysine-358 and lysine-399. Quantitative analysis of the specific radioactivity of each peptide/mol lysine leads to the conclusion that only lysine-105, lysine-154, lysine-269 and lysine-358 participate in cross-links, lysine-269 and lysine-358, respectively, being at isologous and lysine-105 cross-linked with lysine-154 at heterologous contact domains of the enzyme. A model for the planar arrangement of the trimeric species in the quaternary structure of glutamate dehydrogenase is discussed. It includes both isologous and heterologous contact areas between the polypeptide chains.

Amino Acid Sequence↗
PubMed1977

Studies of glutamate dehydrogenase. Methionine-169: the preferentially carboxymethylated residue.

In phosphate buffer at pH 7.0, 5,5'-dithio-bis(2-nitrobenzoic acid), N-ethylmaleimide or iodoacetamide do not alter the activity of beef liver glutamate dehydrogenase. Iodoacetate, however, inactivities the enzyme irreversibility by alkylation. Combined addition of the coenzyme NADH and the substrate 2-oxoglutarate or the effector GTP protects against this inactivation. The alkylation reaction is independent of pH between pH 6-9 indicating that amino, imidazole or phenolic groups are probably not involved in this reaction. Titration of the thiol groups, after denaturation of the enzyme, revealed the loss of approximately one group per polypeptide chain. However, this is not due to the exclusive alkylation of a cysteine residue, since alkylation with iodo-[2-14C]acetic acid also labels a methionine residue. 50% of the label is incorporated into methionine-169 and only 7% into cysteine-115, the remaining radioactivity is distributed in minor quantities (4%) in several unidentified residues. A probable cause of the erroneous thiol groups titration is discussed.

Amino Acid Sequence↗
PubMed1976

Studies of glutamate dehydrogenase. Regulation of glutamate dehydrogenase from Candida utilis by a pH and temperature-dependent conformational transition.

Glutamate dehydrogenase from Candida utilis undergoes a reversible conformational transition between an active and an inactive state at low pH AND low temperature. This conformational transition can also be followed by fluorescence measurements. The temperature-dependent equilibrium between the active and the inactive state is characterized by a transition temperature of 10.7 degrees C and a delta H value of 148 kcal/mol (620 kJ/mol). The temperature dependence of the enzymic activity above 15 degrees C yields an activation energy of 15 kcal/mol (63 kJ/mol), a larger value than that for the beef liver enzyme (9 kcal/mol; 38 kJ/mol). In contrast to the yeast enzyme the Arrhenius plot is linear and, therefore, the beef liver enzyme is not transformed into an inactive conformation at low temperatures. Sedimentation analysis shows that the inactivation of the Candida utilis enzyme is not caused by change in the quaternary structure. The pH dependence of the conformational transition at low pH measured by fluorescence change is characterized by a pK value of 7.01 for the enzyme in the absence and of 6.89 for the enzyme in the presence of 2-oxoglutarate with a Hill coefficient of 3.4 in both cases. Similar results are found when the pH dependence of the enzymic activity is analyzed. With the beef liver enzyme the same pK value is obtained but with a Hill coefficient of 1 indicating cooperativity only in the case of the Candida utilis enzyme. The best fit of the pH dependence of the rate constants of the fluorescence changes was obtained with pK values of 7.45 and 6.45 for the active and the inactive state respectively. In this model the lowest time constant which is obtained at the pH of the equilibrium was found to be 0.05 s-1. Preincubation experiments with the substrate 2-oxoglutarate but not with the coenzyme shift the equilibrium to the active conformation. The coenzyme obviously reduces the rate constant of the conformational transition. The sedimentation coefficient (SO20, w) and the molecular weight were found to be 11.0 S and 276 000, respectively. The enzyme molecule is built up by six polypeptide chains each having a molecular weight of 47 000.

Binding Sites↗
PubMed1975

Investigation of the symmetry of oligomeric enzymes with bifunctional reagents.

The symmetry of proteins composed of identical polypeptide chains has been investigated by means of cross-linking with bifunctional reagents and subsequent sodium dodecylsulfate-polyacrylamide gel electrophoresis. The majority of the investigations were performed with diimidates of different chain lengths (C3-C12), which react exclusively with amino groups. Aldolase, catalase, fumarase, pyruvate kinase, tetrameric proteins with identical polypeptide chains, reveal a D2 symmetry, i.e. they appear to be composed of two pairs of polypeptide chains. The validity of this conclusion is demonstrated with lactate dehydrogenase. This enzyme, shown by X-ray analysis to have a D2 symmetry, yields after cross-linking and subsequent polyacrylamide electrophoresis the band pattern expected for a protein with this quaternary structure and similar to the pattern obtained with the above enzymes. 2. The influence of the experimental conditions on the cross-linking reaction has been investigated. The selectivity of the bifunctional reagent for the different contact domains within the quaternary structure of a protein depends on the reaction time, the chain length and on the concentration of the reagent. In general the D2 symmetry becomes more obvious with increasing chain length and with increasing concentration of the diimidate. Diethylpyrocarbonate showed very little selectivity.

Binding Sites↗
PubMed1975

Quantitative analysis of mixed association between different protein molecules. Physico-chemical and enzymatic properties of rat-liver glutamate dehydrogenase.

The theoretical and experimental analysis of a reversible association-dissociation equilibrium between different proteins (mixed association) is described. The experiments were performed with glutamate dehydrogenases from beef and rat liver. These enzymes are different, especially with respect to their association behavior. The association constant of rat liver glutamate dehydrogenase has been determined by light-scattering measurements. Its value (1.3 x 10(-4) M(-1)) is much lower than that of the beef liver enzyme, but the difference in the free association energy is only 30%. Association between these two enzymes is observed, also employing light-scattering experiments. Theoretical curves for mixed associating systems have been calculated and by comparison with these curves the mixed association constant could be determined. Since the free association energy of the mixed association is very near to the arithmetic mean between the values for the pure enzymes, the association interactions appear to be additive. The model of an open association with a virial coefficient is also true for the rat enzyme and the mixed association. The ultracentrifuge data are also explained by the same model and yield a similar value for the mixed association constant. Differences in the enzyme kinetics are small, but a somewhat reduced lifetime of the ternary complexes with the coenzymes and with subs-rates or GTP can be concluded for the rat liver enzyme. The circular dichroism measurements indicate no significant difference in the dissociation constants of the nucleotides, but the different amplitudes of the ellipticity indicate small differences in the electrical environment of the active center.

Animals↗
PubMed1975

Studies of glutamate dehydrogenase: analysis of functional areas and functional groups.

1. It is shown by limited tryptic digestion of beef liver glutamate dehydrogenase under native conditions that the amino terminus of the polypeptide chain is located at the surface of the molecule. End-group analysis after trypsin treatment yields aspartic acid as the new N-terminal amino acid while the C-terminal threonine remains unchanged. 2. NADH, especially in the presence of 2-oxoglutarate, protects the enzyme against tryptic degradation. In the absence of the coenzyme, glutamate dehydrogenase is rapidly inactivated. 3. The regulatory effects of ADP and GTP are only slightly altered by trypsin. A small shift of the pH dependence of the activation by ADP is observed. 4. The quaternary structure of the unimer of the enzyme is not affected by limited tryptic digestion indicating that the N-terminal part of the polypeptide chain is not located in the contact domains between the polypeptide chains. The association of the hexamer to large associated particles is reduced but not abolished. 5. It is shown by treatment of the enzyme with iodo[2(-14)C]acetic acid as well as with Ellman's reagent that the six - SH groups of the polypeptide chain are buried and not accessible to these reagents in phosphate buffer. In Tris buffer they become exposed and react in the order 89, 55, 197, 115, 270, 319. This together with the result that in Tris buffer the rat of inactivation caused by trypsin is higher than in phosphate buffer indicates that Tris buffer changes drastically the properties of the enzyme. 6. Cross-linking of the enzyme molecule with bifunctional reagents and subsequent dodecylsulfate-polyacrylamide electrophoresis shows that the six identical polypeptide chains are arranged in two groups of three. 7. The implications of these results for the tertiary and quaternary structure of beef liver glutamate dehydrogenase are discussed.

Animals↗