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M Renner

Publications and source records attributed to M Renner.

At least 37 records · Page 2Linked to original sources
PubMed1992

Thermodynamics of unfolding of the alpha-amylase inhibitor tendamistat. Correlations between accessible surface area and heat capacity.

Unfolding of the small alpha-amylase inhibitor tendamistat (74 residues, 2 disulfide bridges) has been characterized thermodynamically by high sensitivity scanning microcalorimetry. To link the stability parameters with structural information we use heat capacity group parameters and water accessible surface areas to calculate the change in heat capacity on unfolding of tendamistat. Our results show that both the group parameter and surface area approaches provide a reasonable, though not perfect, basis for delta Cp calculations. When using the experimentally determined temperature-independent heat capacity increase of 2.89 kJ mol-1 K-1 tendamistat exhibits convergence of thermodynamic parameters at about 140 degrees C, in agreement with recent predictions of the temperature at which the hydrophobic hydration is supposed to disappear. Despite the apparent support of this new view of the hydrophobic effect, there are inconsistencies in the interpretation of the thermodynamic parameters and these are addressed in the Discussion. The specific stability of tendamistat is similar to that of modified bovine pancreatic trypsin inhibitor, with only two of the native three disulfide bridges intact. This observation confirms our previous conclusion that disulfide bridges affect significantly the enthalpy and entropy of unfolding. The recent study by Doig & Williams provides additional convincing support for this conclusion. The predictive scheme proposed by these authors permits a fair estimate of the Gibbs free energy and enthalpy changes of these two proteins.

Amino Acid Sequence↗
PubMed1992

Activation of beta-adrenergic receptors inhibits Ca2+ entry-mediated generation of inositol phosphates in the guinea pig myometrium, a cyclic AMP-independent event.

In the guinea pig myometrium, carbachol, oxytocin, and fluoroaluminates stimulated the breakdown of phosphatidylinositol 4,5-bisphosphate, which was insensitive to pertussis toxin [Biochem. J. 255:705-713 (1988)]. We now demonstrate that an increased accumulation of inositol phosphates, with an early production of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], could also be obtained with K+ (30 mM) and the Ca2+ ionophore ionomycin. Removal of extracellular Ca2+ or addition of the Ca2+ channel antagonists nifedipine and verapamil almost totally abolished stimulations elicited by high K+ and partially attenuated receptor- and fluoroaluminate-mediated increases in inositol phosphates. Isoproterenol similarly attenuated the accumulation of inositol phosphates elicited by carbachol, oxytocin, and fluoroaluminates (maximal inhibition, 35%; EC50, 0.5 nM), with no change in the rate of Ins(1,4,5)P3, inositol bisphosphate, and inositol monophosphate generation. The beta-adrenergic receptor-induced inhibition was prevented by pertussis toxin and could not be reproduced by forskolin, indicating that cAMP was not involved. Experimental findings were, rather, consistent with a predominant role for Ca2+. Thus, inhibition due to isoproterenol was lost in a Ca(2+)-depleted medium and was not additive with that caused by nifedipine. Accumulation of inositol phosphates triggered by high K+ was insensitive to the beta-adrenergic receptor inhibition. The inhibitory effect of isoproterenol, similar to that of nifedipine, was counteracted by ionomycin and also by the Ca2+ channel agonist Bay K 8644. These data indicate that in the myometrium 1) phospholipase C can be activated through a voltage-gated Ca2+ entry-dependent process that contributes at least partially to the stimulations triggered by receptor- and/or guanine nucleotide-binding protein-mediated activation and 2) beta-adrenergic receptor activation is linked via a cAMP-independent, pertussis toxin-sensitive pathway to an inhibition of voltage-gated Ca2+ channels, resulting in an attenuation of the Ca(2+)-associated generation of inositol phosphates.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Alternatively folded states of an immunoglobulin.

Well-defined, non-native protein structures of low stability have been increasingly observed as intermediates in protein folding or as equilibrium structures populated under specific solvent conditions. These intermediate structures, frequently referred to as molten globule states, are characterized by the presence of secondary structure, a lack of significant tertiary contacts, increased hydrophobicity and partial specific volume as compared to native structures, and low cooperativity in thermal unfolding. The present study demonstrates that under acidic conditions (pH less than 3) the antibody MAK33 can assume a folded stable conformation. This A-state is characterized by a high degree of secondary structure, increased hydrophobicity, a native-like maximum wavelength of fluorescence emission, and a tendency toward slow aggregation. A prominent feature of this low-pH conformation is the stability against denaturant and thermal unfolding that is manifested in highly cooperative reversible phase transitions indicative of the existence of well-defined tertiary contacts. These thermodynamic results are corroborated by the kinetics of folding from the completely unfolded chain to the alternatively folded state at pH 2. The given data suggest that MAK33 at pH 2 adopts a cooperative structure that differs from the native immunoglobulin fold at pH 7. This alternatively folded state exhibits certain characteristics of the molten globule but differs distinctly from it by its extraordinary structural stability that is characteristic for native protein structures.

Amino Acids↗
PubMed1991

Stereochemistry and size of sugar head groups determine structure and phase behavior of glycolipid membranes: densitometric, calorimetric, and X-ray studies.

The role carbohydrate moieties play in determining the structure and energetics of glycolipid model membranes has been investigated by small- and wide-angle X-ray scattering, differential scanning densitometry (DSD), and differential scanning microcalorimetry (DSC). The dependence of a variety of thermodynamic and structural parameters on the stereochemistry of the OH groups in the pyranose ring and on the size of the sugar head group has been studied by using an homologous series of synthetic stereochemically uniform glyceroglycolipids having glucose, galactose, mannose, maltose, or trimaltose head groups and saturated ether-linked alkyl chains with 10, 12, 14, 16, or 18 carbon atoms per chain. The combined structural and thermodynamic data indicate that stereochemical changes of a single OH group in the pyranose ring can cause dramatic alterations in the stability and in the nature of the phase transitions of the membranes. The second equally important determinant of lipid interactions in the membrane is the size of the head group. A comparison of lipids with glucose, maltose, or trimaltose head groups and identical hydrophobic moieties has shown that increasing the size of the neutral carbohydrate head group strongly favors the bilayer-forming tendency of the glycolipids. These experimental results provide a verification of the geometric model advanced by Israelachvili et al. (1980) [Israelachvili, J. N., Marcelja, S., & Horn, R. G. (1980) Q. Rev. Biophys. 13, 121-200] to explain the preferences lipids exhibit for certain structures. Generally galactose head groups confer highest stability on the multilamellar model membranes as judged on the basis of the chain-melting transition. This is an interesting aspect in view of the fact that galactose moieties are frequently observed in membranes of thermophilic organisms. Glucose head groups provide lower stability but increase the number of stable intermediate structures that the corresponding lipids can adopt. Galactolipids do not even assume a stable intermediate L alpha phase for lipids with short chain length but perform only Lc----HII transitions in the first heating. The C2 isomer, mannose, modifies the phase preference in such a manner that only L beta----HII changes can occur. Maltose and trimaltose head groups prevent the adoption of the HII phase and permit only L beta----L alpha phase changes. The DSD studies resulted in a quantitative estimate for the volume change associated with the L alpha----HII transition of 14-Glc. The value of delta v = 0.005 mL/g supports the view that the volume difference between L alpha and HII is minute.(ABSTRACT TRUNCATED AT 400 WORDS)

Calorimetry, Differential Scanning↗
PubMed1990

Stability of recombinant Lys25-ribonuclease T1.

The conformational stability of recombinant Lys25-ribonuclease T1 has been determined by differential scanning microcalorimetry (DSC), UV-monitored thermal denaturation measurements, and isothermal Gdn.HCl unfolding studies. Although rather different extrapolation procedures are involved in calculating the Gibbs free energy of stabilization, there is fair agreement between the delta G degrees values derived from the three different experimental techniques at pH 5, theta = 25 degrees C: DSC, 46.6 +/- 2.1 kJ/mol; UV melting curves, 48.7 +/- 5 kJ/mol; Gdn.HCl transition curves, 40.8 +/- 1.5 kJ/mol. Thermal unfolding of the enzyme is a reversible process, and the ratio of the van't Hoff and calorimetric enthalpy, delta HvH/delta Hcal, is 0.97 +/- 0.06. This result strongly suggests that the unfolding equilibrium of Lys25-ribonuclease T1 is adequately described by a simple two-state model. Upon unfolding the heat capacity increases by delta Cp degrees = 5.1 +/- 0.5 kJ/(mol.K). Similar values have been found for the unfolding of other small proteins. Surprisingly, this denaturational heat capacity change practically vanishes in the presence of moderate NaCl concentrations. The molecular origin of this effect is not clear; it is not observed to the same extent in the unfolding of bovine pancreatic ribonuclease A, which was employed in control experiments. NaCl stabilizes Lys25-ribonuclease T1. The transition temperature varies with NaCl activity in a manner that suggests two limiting binding equilibria to be operative. Below approximately 0.2 M NaCl activity unfolding is associated with dissociation of about one ion, whereas above that concentration about four ions are released in the unfolding reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Calorimetry, Differential Scanning↗
PubMed1988

Chloride mediated inhibition of the phosphate and the sulfate transport by dipyridamole in human erythrocyte ghosts.

The inhibition of the unidirectional phosphate and sulfate flux in human erythrocyte ghosts by dipyridamole has been investigated. The inhibition of the phosphate and the sulfate flux is mediated by chloride. At zero chloride, dipyridamole was found to be completely ineffective. At 10 mM chloride, dipyridamole acts as a noncompetitive inhibitor of the phosphate and the sulfate flux and elicits an up to 95% inhibition of the phosphate and the sulfate transport. The results of our studies provide strong evidence for a cooperative binding of chloride and of dipyridamole to the non-protonated form of the band 3 membrane domain.

Biological Transport↗
PubMed1988

Isolation of a 50 kDa polypeptide from the detergent-resistant unfertilized sea urchin egg cytomatrix and evidence for its change in organization during mitosis.

In this report, we describe the isolation of a 50 kDa polypeptide from the detergent-resistant cytomatrix of unfertilized sea urchin egg. This polypeptide shares with the intermediate filaments the property of insolubility in high ionic strength buffer solution. However, it does not cross-react with anti-vimentin and anti-cytokeratin antibodies. Studies performed by indirect immunofluorescence microscopy with an immunospecific serum raised against this polypeptide show that during the first cell cycle the polypeptide exhibits similar configuration changes as those described for tubulin. Using immunocytochemical light and electron microscopy, we present evidence indicating that this 50 kDa polypeptide is a constituent of the isolated mitotic apparatus; it is mainly located on patches of microfibrillar material found close to the microtubules. The 50 kDa polypeptide is not extracted from taxol-assembled microtubules by the 0.6 M NaCl treatment. However, the difference in solubility between this protein and the previously studied microtubule-associated proteins does not preclude the possibility of the 50 kDa polypeptide on being a "microtubule-associated protein". The possible significance of this novel cytoskeletal component is discussed.

Animals↗
PubMed1983

X-ray absorption spectroscopic studies of high valent iron porphyrins. Horseradish peroxidase compounds I and II and synthetic models.

X-ray absorption edge and extended x-ray absorption fine structure studies have been undertaken on resting (ferric) horseradish peroxidase, HRP compound I (HRP-I), HRP compound II (HRP-II), and several highly oxidized synthetic iron porphyrins that may have relevance as models for the iron site in horseradish peroxidase. The energies of the absorption edges are consistent with an Fe(IV) formulation for the highly oxidized species. The shapes of the absorption edges further support the assignment of HRP-I and one of the model compounds as Fe(IV)-porphyrin pi-cations. The edge shapes also demonstrate that the iron sites in the model porphyrins are not identical to the iron sites in the enzyme. Preliminary curve fitting analysis of the extended x-ray absorption fine structure clearly indicates the presence of two different nearest neighbor distances for the iron, both in HRP-I and HRP-II, as well as in two of the highly oxidized model porphyrins. These distances are interpreted as an iron-porphyrin nitrogen distance and as a short (approximately 1.6 A) iron-oxygen distance.

Electron Probe Microanalysis↗