Alfred Blume

Publications (186) View all

• Article: NMR probe for pressure-jump experiments up to 250 bars and 3 ms jump time.

  U Heuert, M Krumova, G Hempel, M Schiewek, A Blume
  [show abstract] [hide abstract]
  ABSTRACT: We describe the design and performance of a pressure-jump instrument for time-resolved NMR experiments. Initial pressure of up to 250 bars can be produced by means of a HPLC pump and distilled water as a pressure-transmitting liquid. Fast pressure release at a time resolution of 3 ms is achieved using a fast acting valve driven by a piezostack close to the sample chamber. The pressure-jump cell is placed together with two valves in an especially designed NMR probe, which can be used in standard spectrometers with wide-bore magnets. All functions of the instrument are personal computer controlled. The equipment is designed for investigations on systems of biological interest, especially lipid-water dispersions. A theoretical consideration implies that probably the limited speed of valve opening determines the lower boundary of the jump time. The performance is illustrated by time-resolved NMR spectra across the phase transition of a phospholipid-water dispersion after a pressure jump from 100 bars to atmospheric pressure.
  The Review of scientific instruments 10/2010; 81(10):105102. · 1.52 Impact Factor
• Article: Thermodynamic Characteristics of A Human Insulin-Deae-Dextran Complex Entrapped in Liposomes

  A. Monosrol, A. Blume, J. Manosrol, K. H. Bauer
  [show abstract] [hide abstract]
  ABSTRACT: Abstract Binding parameters were measured for a study of in vitrocomplexation interaction of human insulin with diethylaminoethyl (DEAE) dextran polymer by a diaultrafiltration (rapid dialysis). The complex was found to have appearent affinity constants of 22.9, 3.2 and 1.5 M-1 at 25°C, 37°C and 45°C respectively in 0.067 M phosphate buffer at pH 7.4. The complexation reaction was found to be exothermic with an enthalpy change (AH) of 26 kcalhole. Differential scanning calorimetry (DSC) was used to obtain the temperatures and enthalpies for the insulin denaturation process in the presence of the DEAE-dextran polymer and liposomal membranes. The human insulin-DEAE-dextran complex appears to have a higher denaturation temperature with a higher denaturation enthalpy than the free human insulin in 0.067 M phosphate buffer at pH 7.4 solution. The uncomplexed human insulin entrapped in dimyristoyl phosphatidylcholine (DMPC) liposomes and neutral liposomes (DMPC/cholesterol = 1 : 1) did not differ significantly in temperature and enthalpy of denaturation from the unentrapped protein. Conversely, the complexed insulin entrapped in liposomes indicated an unchanged denaturation temperature but a lower denaturation enthalpy compared to the complexed human insulin not entrapped. The complexed human insulin entrapped in positively charged liposomes prepared from DMPC/cholesterol/stearylamine in the molar ratio of 7:2:1 showed a slight change in denaturation temperatures and lower denaturation enthalpies than the complexed protein not entrapped whereas the uncomplexed human insulin gave three peaks of different denaturation temperatures and enthalpies.
  10/2008; 16(5):837-854.
• Chapter: Application of titration calorimetry to study binding of ions, detergents, and polypeptides to lipid bilayers

  A. Blume, J. Tuchtenhagen, S. Paula
  [show abstract] [hide abstract]
  ABSTRACT: The binding of ions, the incorporation of detergents and polypeptides into lipid bilayers, and the CMC and heat of micellization of detergents were studied by titration calorimetry. The heat of dissociation of dimyridstoylphosphatidic acid (DMPA−+OH−⇌DMPA2−+H2O) was investigated as a function of temperature covering the phase transition of singly and doubly charged DMPA. The intrinsic pK0 for the dissociation was determined from the tiration curves applying the Gouy-Chapman theory. pK0 decreases with temperature from ca.6.2 at 11°C to 5.4 at 54°C. The temperature dependence of the dissociation enthalpy ΔHDiss was combined with DSC data on the transition enthalpies ΔHTrans for DMPA in its two ionization states to construct a complete enthalpy vs. temperature diagram. Titration calorimetry was also used to determine the CMC and the heat of micellization of the detergents SDS, octylglucoside, Na-cholate, and Na-deoxycholate. From the temerature dependence of the CMC and the heat of micellization the thermodynamic functions ΔG and ΔS were determined as a function of temperature. The interaction of Na-deoxycholate with lipid bilayers was studied at a temperature where the heat of mizellization was zero. Complex titration peaks were observed, indicating incorporation reactions on different time scales. The heats of reaction depended on the nature of the phospholipid. Titration calorimetry was also used to study the binding of melitton to lipid vesicles. The sign of the heat of incorporation depended on whether the lipid was in the gel or the liquid-crystalline state and on the chemical nature of the phospholipid.
  03/2008: pages 118-122;
• Article: Mechanism of islet amyloid polypeptide fibrillation at lipid interfaces studied by infrared reflection absorption spectroscopy.

  D H J Lopes, A Meister, A Gohlke, A Hauser, A Blume, R Winter
  [show abstract] [hide abstract]
  ABSTRACT: Islet amyloid polypeptide (IAPP) is a pancreatic hormone and one of a number of proteins that are involved in the formation of amyloid deposits in the islets of Langerhans of type II diabetes mellitus patients. Though IAPP-membrane interactions are known to play a major role in the fibrillation process, the mechanism and the peptide's conformational changes involved are still largely unknown. To obtain new insights into the conformational dynamics of IAPP upon its aggregation at membrane interfaces and to relate these structures to its fibril formation, we studied the association of IAPP at various interfaces including neutral as well as charged phospholipids using infrared reflection absorption spectroscopy. The results obtained reveal that the interaction of human IAPP with the lipid interface is driven by the N-terminal part of the peptide and is largely driven by electrostatic interactions, as the protein is able to associate strongly with negatively charged lipids only. A two-step process is observed upon peptide binding, involving a conformational transition from a largely alpha-helical to a beta-sheet conformation, finally forming ordered fibrillar structures. As revealed by simulations of the infrared reflection absorption spectra and complementary atomic force microscopy studies, the fibrillar structures formed consist of parallel intermolecular beta-sheets lying parallel to the lipid interface but still contain a significant number of turn structures. We may assume that these dynamical conformational changes observed for negatively charged lipid interfaces play an important role as the first steps of IAPP-induced membrane damage in type II diabetes.
  Biophysical Journal 12/2007; 93(9):3132-41. · 3.65 Impact Factor
• Article: Influence of poly(L-lysine) on the structure of dipalmitoylphosphatidylglycerol/water dispersions studied by X-ray scattering.

  G Förster, C Schwieger, F Faber, T Weber, A Blume
  [show abstract] [hide abstract]
  ABSTRACT: The interaction between the negatively charged phospholipid DPPG and positively charged poly(L: -lysine) (PLL) of different lengths was studied by X-ray scattering in the SAXS and WAXS region. As a reference pure DPPG (Na salt) was investigated over a wide temperature range (-30 to 70 degrees C). The phase behavior of DPPG in aqueous and in buffer/salt dispersions showed a metastable subgel phase at low temperatures and a recrystallization upon heating before reaching the liquid-crystalline phase. The presence of additional salt stabilizes the bilayer structure and decreases the recrystallization temperature. Large changes in the SAXS region are not connected with changes in chain packing. In DPPG/PLL samples, the PLL is inserted between adjacent headgroup layers and liberates counterions which give rise to a freezing point depression. In the complex with DPPG PLL form an alpha-helical secondary structure at pH 7 and temperatures below the gel to liquid-crystalline phase transition. This prevents DPPG from recrystallization and strongly increases the stacking order. The lamellar repeat distance is decreased and fixed by the helix conformation of PLL in the gel phase. PLL with n = 14 is too short to form helices and is squeezed out reversibly from the interbilayer space upon cooling by freezing of trapped water. In dispersions with longer PLLs (n > 400) at -20 degrees C a 1D crystallization of PLL alpha-helices in the aqueous layer between the headgroups takes place. A structural model is presented for the lateral periodic complex, which is similar to the known cationic lipid/DNA complex.
  European Biophysics Journal 05/2007; 36(4-5):425-35. · 2.14 Impact Factor