Petr Munk

α-Keto acid dehydrogenase complexes: XVI. Studies on the subunit structure of the pyruvate dehydrogenase complexes from bovine kidney and heart☆

Abstract The mammalian pyruvate dehydrogenase complex contains a core, consisting of dihydrolipoyl transacetylase, to which pyruvate dehydrogenase and dihydrolipoyl dehydrogenase (a flavoprotein) are joined. Electron microscopic studies indicated that the design of the transacetylase is based on icosahedral (532) symmetry and, therefore, it would be expected to contain 60 very similar, if not identical, polypeptide chains. Evidence is presented that the bovine kidney and heart dihydrolipoyl transacetylases are very similar and that each enzyme does indeed consist of 60 apparently identical polypeptide chains. Each chain apparently contains 1 molecule of covalently bound lipoic acid. The molecular weight of the transacetylase is about 3.12 ± 0.20 million. The pyruvate dehydrogenase components of the bovine kidney and heart pyruvate dehydrogenase complexes are also very similar. The uncomplexed enzymes have a molecular weight of about 154,000 and possess the subunit structure α2β2. The molecular weights of two subunits are about 41,000 and 36,000, respectively. Only the α-subunit undergoes phosphorylation in the presence of pyruvate dehydrogenase kinase and ATP. Possible functions of the two subunits are discussed. It appears that the bovine kidney and heart pyruvate dehydrogenase complexes contain about 60 pyruvate dehydrogenase units (αβ) but only 10–12 flavoprotein chains.

Solvents and Self-Organization of Polymers

Overview of Polymer Micelles Z. Tuzar. Equilibrium and Nonequilibrium Polymer Micelles P. Munk. Block Copolymers: Syntheses, Colloidal Properties and Application Possibilities of Micellar Systems G. Riess, G. Hurtrez. Micellization of Ionic Block Copolymers in Three Dimensions M. Moffitt, et al. Micellization of Block Copolymers in Two Dimensions C.J. Clarke. Site Specific Drug-Carriers: Polymeric Micelles as High Potential Vehicles for Biologically Active Molecules S. Cammas, K. Kataoka. Experimental Results on Hydrophobe Release E. Arca. Solubilization of Hydrophobic Substances by Block Copolymer Micelles in Aqueous Solutions R. Nagarajan. Monte Carlo Simulations of Self-Assembly in Macromolecular Systems T. Halilogu, W.L. Mattice. Self-Assemblies in Ion-Containing Polymers A.R. Khokhlov, O.E. Philippova. Equilibrium Structure of Ionizable Polymer Brushes E. Zhulina. Structure and Interactions in Tethered Chains A.P. Gast. Block Copolymer Self-Assembly at Surfaces: Structure and Properties M. Tirrell. Copolymer Micelles in Aqueous Media Z. Tuzar. The Structure of Telechelic Associating Polymers in Water A. Yekta, et al. Unimolecular Micelles of Hydrophobically Modified Polyelectrolytes Y. Morishima. Thermally Induced Phase Separation of Poly(Ethoxy-Ethyl- Vinyl Ether) Studied by the Fluorescence Method J. Horinaka, et al. Classical Methods for the Study of Block Copolymer Micelles P. Munk. Development of Synchrotron SAXS/Diffraction Instrumentation B. Chu. Structure and Dynamics of Polymers by Synchrotron SAXS B. Chu. From the Ruler to the Sextant: Dipole-Dipole Electronic Energy Transfer as a Tool for Probing Polymer Conformation and Morphology A. Yekta, M.A. Winnik. Use of Fluorescence Methods to Characterize the Interior of Polymer Micelles S.E. Webber. Fluorescence Depolarization Method to Study Polymer Chain Dynamics M. Yamamoto, et al.

α-Keto acid dehydrogenase complexes: XVIII. Subunit composition of the Escherichia coli pyruvate dehydrogenase complex☆

Abstract The Escherichia coli Crookes pyruvate dehydrogenase complex contains a core, consisting of dihydrolipoyl transacetylase, to which pyruvate dehydrogenase and dihydrolipoyl dehydrogenase (a flavoprotein) are joined by noncovalent bonds. Electron microscopic studies indicated that the design of the transacetylase is based on octahedral (432) symmetry and, therefore, it would be expected to contain 24 very similar, if not identical, polypeptide chains. Evidence is presented that the transacetylase does indeed consist of 24 apparently identical polypeptide chains. Each dehydrogenase (about 112,000). Both the uncomplexed pyruvate dehydrogenase and the flavoprotein contain two apparently identical polypeptide chains. The available data do not permit a decision as to whether each of these enzymes is present in the complex as a monomer or a dimer. It appears that the E. coli Crookes pyruvate dehydrogenase complex contains 24 pyruvate dehydrogenase chains, 24 dihydrolipoyl transacetylase chains, and 12 flavoprotein chains. Possible distributions of the pyruvate dehydrogenase chains and the flavoprotein chains around the transacetylase core are discussed.

Automatic measurement of intereference photographs from the ultracentrifuge

Abstract With a computer-linked densitometer and an algorithm built around the Fourier transform, it is possible to automate the reading of Rayleigh interference patterns such as those obtained from an analytical ultracentrifuge. Measurements of fringe position are at least as precise as data collected manually.

Formation of block copolymer micelles: a sedimentation study

Abstract The formation of block copolymer mixed micelles has been studied in solutions of polystyrene-block-polyisoprene and polystyrene-block-poly(ethylene-co-propylene) in decane, a selectively poor solvent for polystyrene blocks. The rate of mass exchange between two types of micelles, studied by the sedimentation velocity method, depends strongly on the rates of micelle formation and dissociation processes, which can be controlled by temperature.

Release of Hydrophobic Substances from Polystyrene-Methacrylic Acid Block Copolymer Micelles into Aqueous Media

Abstract Block copolymer micelles are potential carriers for controlled-release drug delivery. In this study, the fundamental aspects of the release of a model compound from the micelles into the surrounding media were explored. A fluorescence-based technique was developed for following the release of the model compound from the cores of block copolymer micelles into aqueous media. The experimental release curves were compatible with theoretical dependences for diffusion controlled release from spherical particles. The diffusion coefficients found were of the order of 1018 cm2/s, which was expected for molecules with sizes of our probes and glassy polystyrene. The partition coefficients are also of the expected order of 105 magnitude. The fraction of the probe present outside of the cores at the start of the experiment may serve to characterize the efficiency of various procedures for the loading of various agents into the core.

Equilibrium and Nonequilibrium Polymer Micelles

Block copolymer micelles and detergent micelles have many common features. The detergent micelles are equilibrium systems. If their equilibrium is disturbed by some outside action, they reequilibrate within a very small fraction of a second. Consequently, in many studies of block copolymer micelles, it is tacitly assumed that they are also at equilibrium and that their properties faithfully reflect the underlying equilibrium thermodynamics. It is the purpose of this article to show that truly equilibrium block copolymer micelles are rare and that the equilibrium is difficult to recognize.

Solubilization and release of hydrophobic compounds from block copolymer micelles. II. Release of pyrene from polyelectrolyte micelles under equilibrium conditions

The kinetics of the release of pyrene from poly(tert-butyl acrylate)-block-poly(2-vinylpyridine) polyelectrolyte micelles into aqueous media was studied by two independent experimental fluorometric techniques. Mathematical treatment of the time-dependent fluorescence intensities based on a model of diffusion from a sphere allowed the evaluation of the diffusion coefficient of pyrene in the dense poly(tert-butyl acrylate) micellar core. Assumptions necessary for mathematical treatment of experimental curves were tested and their validity was proved. Fluorometric measurements suggest that a considerable fraction of pyrene is solubilized also in poly(2-vinylpyridine) micellar shells.

Birefringence of Solutions of Rigid Particles in Steady and Oscillatory Flow

Theories of flow birefringence in steady and oscillatory shear flow for spheroidal particles are compared. It is shown, that proper normalization of birefringence functions make them identical for both flows at low gradients and frequencies. The deviations at high gradients and frequencies increase with increasing particle axial ratio. The theory for polydisperse particles is developed. From the limiting behavior at low and high gradients and frequencies it is possible to find various averages of the relaxation times of the particles and hence some description of the polydispersity. The differences between steady and oscillatory flow behavior for a monodisperse system persist even for the polydisperse case thus giving the possibility of indirectly checking some aspects of the monodisperse theory. Experiments on microcrystalline alumina (Baymal), tobacco mosaic virus, and bentonite are in essential agreement with theoretical predictions.

Intermolecular contact interactions and their temperature dependence

A model, based on inverse gas chromatography experiments, has been developed for intermolecular interaction and its temperature dependence. The model ascribes to each substance a four-component solubility parameter; the four components reflect the van der Waals, polar, electron donor, and electron acceptor interactive properties. Their values depend on temperature in the same manner as does the cohesive energy. The latter was found to depend only on the critical temperature, the acentric factor, and the reduced temperature. The model was used for evaluation of the solubility parameters from polymer-solvent interaction coefficients and their temperature dependence with high accuracy. For binary solventsolvent mixtures, the free energy of mixing and its temperature dependence, as well as enthalpy of mixing can be derived from this model with a good accuracy.