Apolar Interactions Research Articles

Influence of the pyruvate content of xanthan on macromolecular association in solution

The unusual increase in viscosity and pseudoplasticity often observed when salts are added to moderately concentrated aqueous solutions of xanthan gum is shown to arise from an increase in the extent of macromolecular association. The fractional change in viscosity on addition of KCl to salt-free 1% (w/v) solutions of purified polysaccharide in the K + salt form is found to be positive only when the degree of pyruvate substitution (fraction of side chains which carry pyruvate ketal substituents) exceeds ≈0.31. Above this value, the fractional change in viscosity increases with further increase in the degree of pyruvate substitution. These differences cannot arise from different degrees of conformational ordering, since the magnitude of the thermally induced order disorder transition (monitored by optical rotation at low ionic strength) is independent of pyruvate content. The temperature at the transition midpoint, however, falls with increasing degree of pyruvate substitution. This is attributed to destabilization of the ordered structure by intramolecular electrostatic repulsion between pyruvate groups, and stabilization through apolar interactions of acetate methyl groups. Viscosity-concentration relationships show changes of slope which mark the onset of macromolecular association. Association commences at lower concentrations when ionic strength and degree of pyruvate substitution are high. It is suggested that once electrostatic repulsions have been diminished at high ionic strength, association is promoted by intermolecular apolar interactions of pyruvate methyl groups, which are suitably near the periphery of the helical conformation.

Alkylated poly(amino acids). I. Conformational properties of poly(Nε‐trimethyl‐L‐lysine) and poly(Nδ‐trimethyl‐L‐ornithine)

AbstractPoly(Nε‐trimethyl‐L‐lysine), [Lys(Me3)]n, and poly(Nδ‐trimethyl‐L‐ornithine), [Orn(Me3)]n, in sodium dodecylsulfate do not assume the β‐structure or α‐helix, respectively, of their parent polymers. In 0.5M Ca(ClO4)2 both [Lys(Me3)]n and [Orn(Me3)]n are aggregated and display CD spectra indicative of a regular, perhaps helical, structure. For [Lys]n and [Lys(Me3)]n, the T1 of the α‐hydrogens are 0.379 and 0.230 sec, respectively, indicating greater rigidity for [Lys(Me3)]n. The CD spectrum of [Lys(Me3)]n at pH 8 is more heat resistant than that of [Lys]n. It is suggested that apolar interactions are more important in the methylated polymers than in the parent polymers.

The conformation and aggregation of bovine β‐casein A. II. Thermodynamics of thermal association and the effects of changes in polar and apolar interactions on micellization

AbstractA sedimentation analysis has been used to determine the proportion of protein present as monomer and aggregate in 0.5 and 1.0 g/dl solutions of β‐casein A in pH 7 phosphate buffer over the temperature range 10–40°C. The amount and molecular weight of the aggregate increase with temperature; under the conditions used, the aggregation number (n) of β‐casein is given approximately by n = 0.6t + 2 with t in degrees centigrade. The concentration of β‐casein in monomeric and aggregated states at different temperatures is used to calculate the standard enthalpy of aggregation ΔH° (Van't Hoff) by assuming that β‐casein undergoes a cooperative, two‐state, micellization process; aggregation is an endothermic process and ΔH° = 66.0 ± 2.6 kJ mol−1. Combination of this ΔH° with the amount of protein calculated to dissociate when 1 g/dl solutions are diluted isothermally to 0.5 g/dl gives the heat of dilution at various temperatures. These calculated heats of dilution are compared with the experimental values obtained by carrying out the same dilutions in a microcalorimeter. The heat of dilution decreases linearly with β‐casein concentration, but the extrapolated zero‐concentration values of 65.8 ± 1.6 kJ mol−1 is the same as the Van't Hoff enthalpy. This agreement in the enthalpy values indicates that the micellization of β‐casein occurs cooperatively. The effect of modifying the hydrophobic/hydrophilic balance of the system on the micellization of β‐casein A has been investigated. The hydrophobic interaction between the protein molecules is decreased by removing the three C‐terminal residues (Ileu Ileu Val) with carboxypeptidase‐A. This modification drastically reduces the ability of the β‐casein molecule to form micelles. Substitution of 2H2O for H2O at constant temperature perturbs the monomer–micelle equilibrium in favor of micelles because of enhanced hydrophobic interactions in the former solvent. The results are consistent with β‐casein micellization involving a delicate balance of the hydrophobic forces favoring aggregation and electrostatic forces opposing it.

Substrate specificity and other properties of DOPA decarboxylase from guinea pig kidneys

DOPA decarboxylase (aromatic- l-amino-acid carboxy-lyase, EC 4.1.1.28) from guinea pig kidneys has been purified to a specific activity of 9370 or 330-fold. Efficient purification was possible by employing apolar interaction chromatography. The purified enzyme gives a single component on polyacrylamide gel electrophoresis and the absorption spectrum of the enzyme reveals two froms of binding of pyridoxal 5-phosphate. The pure enzyme decarboxylates l-DOPA, 5-hydroxytryptophan, o- tyrosine and m- tyrosine but it is inactive towards phenylalanine, tyrosine, tryptophan, histidine and 3-methoxyphenylalanine. The enzyme behaves as an undissociated enzyme but only towards 5-hydroxytryptophan. It behaves as an enzyme from which the coenzyme is partially dissociated when it attacks l-DOPA, o- tyrosine and m- tyrosne .

Axial arrangement of α-chains in the collagen molecule: intramolecular polar and apolar interactions

Polar and apolar intramolecular interactions have been calculated for the type I collagen molecule. These interactions were determined as a function of the relative axial stagger between the three α-chains (two α 1 and one α 2). The results clearly show that a relative stagger of only one residue translation (2.86 Å) between adjacent chains is optimal. The criteria chosen to define the polar and apolar interactions do not distinguish between the three possible ways in which three α-chains in the collagen molecule can be linearly arranged i.e. α 1 α 1 α 2, α 1 α 2 α 1 and α 2 α 1 α 1. It appears probable that this information lies mainly in the non-helical portions of the procollagen molecule.

Analysis of biomaterials deposited on soft contact lenses.

Formation of opaque deposits on the anterior (air) surface of hydrophilic soft contact lenses is a problem worthy of investigation by all concerned. These deposits have been analyzed for biomaterials by chemical, biochemical, electrophoretic, and immunological techniques. Qualitative and quantitative chemical colorimetric tests revealed the presence of variable amounts of protein (5-10 microgram/lens), carbohydrate (1.0-1.2 microgram/lens), and phospholipids (0.01-0.05 micronmole/lens). Cholesterol and glucose were not present at detectable levels. Fluorescent antibody tests with appropriate controls gave positive tests for albumin, lysozyme, gamma-G-globulin, and alpha1-lipoprotein in the deposits, all proteins present in tear fluid. Deposits were most effectively removed from the lenses by the combination of heat, sodium dodecyl sulfate (SDS) detergent, and the thiol reagent dithiothreitol (DTT). SDS-denatured protein migrated on polyacrylamide gels with electrophoretic patterns corresponding to molecular weights for those proteins detected by the above antibody tests. The nature of the bonding interactions of biomaterials to the lenses was probed by chemical reagents used to remove them, employed singly and in all possible combinations. Urea, guanidine hydrochloride, potassium thiocyanate, potassium perchlorate, hydroxylamine, and EDTA were much less effective than SDS and DTT. These data suggest that apolar interactions plus disulfide bonds may be important in stabilizing the deposit structure, and point to improved cleaning procedures.

Purification and molecular properties of bovine heart pyruvate kinase

A rapid method is presented for the purification of pyruvate kinase (ATP: pyruvate 2-O- phosphotransferase , EC 2.7.1.40) from bovine heart. The enzyme obtained is homogeneous by criteria of sodium dodecyl sulphate polyacrylamide electrophoresis and ultracentrifugation and has a specific activity of 260 units/mg. It is a tetramer of 220 000 daltons and S 20, w 0 = 10.0 S and possesses no free amino-terminal residue. The amino acid composition is similar to that of the M 1 isozyme of rabbit and bovine skeletal muscle. The enzyme is subject to polymerisation to a hexamer of the basic tetramer. The polymeric species has a molecular weight of 1320 000, is promoted at low ionic strength and is undetectable at ionic strength greater than 0.2 by either sedimentation equilibrium or sedimentation velocity measurements. The polymerisation is independent of temperature in the range 5–20°C implying that charge interactions rather than apolar interactions are responsible for the process.

Stimulation of transcription on chromatin by polar organic compounds.

Polar organic compounds, including DMSO, increase RNA synthesis on isolated chromatin by E. coli RNA polymerase and RNA polymerase II from calf thymus. Transcription is stimulated on chromatin from Friend-virus-infected erythroleukemia cells and from various other sources. Using procedures which inhibit specifically the formation of a stable initiation complex, it is shown that the stimulation does not result from an increase in initiation of both E. coli and the eukaryotic RNA polymerase. After separation of chromatin into template active and inactive fractions, DMSO increases RNA synthesis by a factor of about 1.5 using the template inactive fraction, while stimulation of transcription on the template active portion is lower (factor of 1.2). It is suggested that the effect on RNA synthesis is mediated by a weakening of the apolar interactions between histones in chromatin subunits, releasing transcription partially from the constraints imposed by histones.

Immunochemical analyses of membrane-bound complement: Detection of the terminal complement complex and its similarity to “intrinsic” erythrocyte membrane proteins

1. (1) Membranes of sheep erythrocytes lysed with antibody and human or rabbit complement were solubilized in non-ionic detergents (Triton X-100 or Berol EMU-043) and analysed immunochemically using antisera directed against individual complement components. The precipitation behaviour of membrane-bound C3, C5, C6 and C9 components of complement was examined by immuno-double diffusion, rocket- and crossed immunoelectrophoresis performed in agarose gels containing 1% non-ionic detergent. 2. (2) Membrane-bound C5, C6 and C9 are antigenically altered compared with the native (serum) components. 3. (3) Immuno-double diffusion in the presence of non-ionic detergent reveals formation of C5-C6-C9 complexes on the membranes; these complexes are stable in non-ionic detergent. No complex formation was detected in serum between native C5, C6 and C9 components. There was also no evidence for complexing between membrane-bound C3, C4 or membrane proteins and the “late-reacting” complement components. 4. (4) The extractability of complement components by various manipulations has been studied by use of quantitative rocket immunoelectrophoresis. Up to 65% of membrane-bound C3 is readily extracted by dialysis of membranes against 1 mM EDTA, pH 8.0, 100 mM EDTA, pH 8.0, 1.2 NaCl plus or minus EDTA, by extraction in isotonic buffers at 37 °C, by heating at 45 °C over several hours, or by treating membranes with 1 mM p- chloromercuribenzoate sulfonate. In contrast, less than 6% of the terminal complement complex can be eluted by any of the described methods or combination of methods. 5. (5) Our data suggest that the terminal complement complex associates with membrane “core” components through apolar interactions.

Conformational states of chymotrypsin at high pH: Temperature effects on catalysis and binding

Studies on the effects of temperature on the chymotrypsin-catalyzed hydrolysis of specific and nonspecific substrates reveal markedly nonlinear Arrhenius and van't Hoff plots. The investigations include the δ- and α-forms of the enzyme at pH 7.8–9.6 and 0–40 °C. Rigorous error-analysis of the data by computer indicates that these nonlinear responses are not artifactual. By determining the effects of temperature and pH on the relative rates of the acylation and deacylation processes, little or no evidence is found for the nonlinear plots being caused by a change in rate-limiting step as these parameters vary. Model calculations also show that van't Hoff plots that are concave downward, as frequently observed here, cannot be produced by a mechanism involving a change in rate-limiting step. A variety of extra-kinetic data support the view that conformation changes in the enzyme are the most likely explanation. Detailed comparisons of activation parameters calculated for each enzyme-substrate interaction show clearly that changes in enthalpy values are compensated for by changes in entropy. Relative to the α-enzyme, δ-chymotrypsin maintains an active-site conformation more favorable for catalysis over a wider temperature range. Different activation parameters dominate the catalytic process with specific substrates, as compared to nonspecific ones. At high pH the binding process is no longer dominated by apolar interactions even with specific substrates, and the enzyme tends to lose its specificity. Overall, the data indicate that the selectivity and, by inference, the structural integrity of the active site decrease as one proceeds from low to high temperature, from neutral to alkaline pH, from δ- to α-chymotrypsin, or from specific to nonspecific amino acid sidechain groups. These studies also have implications for conclusions drawn from data collected at temperatures other than 37 °C.

Cooperative effects involved in esterolytic reactions of cationic long chain esters catalyzed by benzimidazole-containing polymers

The solvolyses of positively charged esters with varying chain length catalyzed by benzimidazole, poly[5(6)-vinylbenzimidazole] and copolymers of 5(6)-vinylbenz-imidazole with acrylic acid were studied. Poly[5(6)-vinylbenzimidazole] showed a marked selectivity for the positively charged esters with varying aliphatic chain length but the catalytic activity was suppressed. In order to investigate the more detailed characteristics of the 5(6)-vinylbenzimidazole-acrylic acid copolymers in the solvolyses of these esters, the effects of copolymer composition on their catalytic activities were studied. In the solvolyses of every ester employed, the copolymer compositions affected their catalytic activities. In 40% 1-propanol-water the activities of the copolymers indicated a strong dependence on the carboxylatebenzimidazole-carboxylate triad. These effects were due to strong electrostatic interactions between these sequences and the substrates. The effects of solvent composition on the catalytic activities of the copolymer-catalyzed solvolyses were also investigated. The copolymers of 5(6)-vinylbenzimidazole with acrylic acid were found to have entirely different characteristics in methanol-water than in 1-propanol-water systems. The catalytic ability was found to be a function of the benzimidazole content and on the size of the substrate. Apolar interactions became a dominant force in the methanol-water system.

Spectral studies of interactions of detergents with tryptophyl compounds.

The interactions of sodium dodecylsulfate and hexadecyltrimethylammonium chloride with typtophyl model compounds were investigated by fluorescence, classical difference spectra and thermal perturbation spectra. Oppositely charged models and detergents interact to produce marked spectral changes. Apolar interactions also contribute. The ease of interaction with sodium dodecylsulfate decreases in the order: tryptamine, Lys‐Trp‐Lys, Leu‐Trp‐Leu, Gly‐Trp‐Gly, Glu‐Trp‐Glu shows little or no interaction. Lys‐Trp‐Lys forms both soluble and insoluble complexes with sodium dodecylsulfate.

The interaction of glutamate dehydrogenase and malate dehydrogenase with phospholipid membranes.

The interaction between sonicated dispersions of purified phospholipids, corresponding to those found in the inner mitochondrial membrane, and the enzymes was studied by kinetic and spectroscopic methods.With glutamate dehydrogenase the charge type of the lipid head group determines the extent of lipid‐protein complexing. Phosphatidylcholine did not significantly alter the activity of the enzyme at lipid concentrations up to 1 mM, and the nuclear magnetic resonance (NMR) spectrum of the lipid (1%, w/v) was not altered in the presence of enzyme (up to 20% w/v). Phosphatidylethanolamine did not affect the activity in the oxidation of glutamate, but interfered with the assay in the reverse direction, possibly owing to Schiff‐base formation with 2‐oxoglutarate. The negatively charged cardiolipin, which is found uniquely in the inner mitochondrial membrane, strongly and reversibly inhibited the enzyme (50% inhibition with 0.1–20 μM lipid, depending on conditions). Another anionic phospholipid, phosphatidylserine (which does not occur in mitochondria), also inhibited the enzyme, but less effectively (50% inhibition at about 8 μM). The lipid‐enzyme interaction decreases with increasing ionic strength, indicating an electrostatic contribution to the binding. NMR studies suggest that there is also an apolar interaction involving the lipid chains.The studies with malate dehydrogenase concentrated on detecting possible stabilization of this enzyme through interaction with lipids. A clear‐cut stabilization was found with lysophosphatidylcholine. Under conditions such that the enzyme alone lost 50% on the initial activity in about 2 h, lysophosphatidylcholine gave a slight (20%) activation and this activity remained constant for several hours. NMR studies indicated that, as with the related enzyme 3‐hydroxybutyrate dehydrogenase, both the polar choline head group and the hydrocarbon chains are involved in the binding of the lipid to the protein.These specific lipid · protein complexes are probably examples of allotopic interactions. This form of complexing may explain aspects of the behaviour of these enzymes in vivo.

Effect of alcohols and neutral salt on the thermal stability of soluble and precipitated acid-soluble collagen.

The effects of mono- and poly-hydric alcohols in the presence of KCl on the intrinsic stability of collagen molecules in dilute acid solution were compared with corresponding solvent and salt effects on the increased stability of the aggregated molecules in salt-precipitated fibrils. Salt addition decreased solubility and increased the thermal stability of fibrils, but progressively decreased the stability of collagen molecules in solution. In contrast, the alcohols enhanced solubility and decreased fibril stability, the effects increasing with solvent hydrocarbon chain length and with decreasing hydroxyl/methylene-group ratio. Molar destabilization of dissolved collagen by alcohols was lower than for fibrils, and at low salt concentration, both ethylene glycol and glycerol were structural stabilizers. Electron-micrograph studies indicated that salt-precipitated fibrils tended to adopt the native aggregation mode, and qualitatively similar solvent effects were observed in insoluble collagens. Implications of the experimental findings are discussed in terms of a model in which electrostatic and apolar interactions mainly govern the excess of stability in collagen fibrils whereas intrinsic stability of single molecules is a function of polar interactions and polypeptide-chain rigidity.

Nuclear magnetic resonance study of lecithin-cholesterol interactions

The interactions of cholesterol with lecithin in excess water have been examined in sonicated dispersions using high resolution nuclear magnetic resonance spectroscopy, and in unsonicated dispersions using wide line nuclear magnetic resonance. Detailed spectroscopic and molecular interpretations are derived by comparison of the lecithin spectra before and after the addition of cholesterol. When dispersed in excess water, lecithin and cholesterol form an equimolar complex which has a lifetime greater than 30 msec. Apolar interactions between the steroid molecule and the first ten methylene groups of each lecithin chain severely restrict the motions of this region of the chains, leaving their terminal methyl ends relatively free. The lecithin phosphate group and cholesterol hydroxyl appear to be juxtaposed and may be hydrogen bonded. In a codispersion where the cholesterol is present in less than equimolar amounts, the complex is not distributed evenly within the bilayers, but forms clusters. Earlier observations on the chain-melting behaviour of lecithin-cholesterol codispersions are correlated with the existence of the complex and with its temperature dependence. The biological significance of the rigidity profiles across lecithin and mixed lecithin-cholesterol bilayers and of the possibility of heterogeneous distributions of complex within the plane of a bilayer is discussed.

Magnetic resonance studies on the components of human erythrocyte membranes

The apoprotein of human erythrocyte membranes was covalently spin-labelled with nitroxide-maleimide and mixed anhydride labels, before and after removal of sialic acids. The e.s.r. spectra and pH-induced spectral changes were compared with the reported spectra of native membranes. Interactions between the apoprotein and other lipids were examined using lipids containing spin probes. Lysolecithin was shown to bind more strongly than other lipids to membrane apoprotein. This binding was compared with the binding of lysolecithin to bovine serum albumin and acid casein. The formation of a lipoprotein complex between positively charged sialic acid free apoprotein and negatively charged sonicated dispersions of membrane lipid in an aqueous medium was examined using spin labels and spin probes. The data demonstrate that both polar and apolar interactions between the lipid and protein are involved in stabilisation of the complex.

A spin label study of the recombined lipid and apoprotein of human ertthrocyte membranes

Covalent spin labels and spin probes have been used to study the binding between sialic-acid free (s.a.f.) apoprotein and total lipid of human erythrocyte membranes during the formation of a lipoprotein complex. The data confirm that both electrostatic and apolar interactions are involved in the recombination.

Enhanced rates due to apolar interactions between polymer and substrate

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEnhanced rates due to apolar interactions between polymer and substrateGarfield P. Royer and I. M. KlotzCite this: J. Am. Chem. Soc. 1969, 91, 21, 5885–5886Publication Date (Print):October 1, 1969Publication History Published online1 May 2002Published inissue 1 October 1969https://doi.org/10.1021/ja01049a039RIGHTS & PERMISSIONSArticle Views118Altmetric-Citations33LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (274 KB) Get e-Alerts Get e-Alerts

Acceleration of p-nitrophenyl ester cleavage due to apolar bonding. A model for biologically significant apolar interactions.

Acceleration of p-nitrophenyl ester cleavage due to apolar bonding. A model for biologically significant apolar interactions.

Ionic equilibria in protein conjugates: Comparison on proteins

The pKa's of dye conjugates of a series of proteins (gelatin, protamine, insulin, lysozyme, ribonuclease, trypsinogen, β-lactoglobulin, ovalbumin, bovine serum albumin) have been determined. In general the shift in pKa increases with increasing molecular weight. Gelatin, however, behaves in a unique way in that apolar interactions are weak. However, this is not due to its denatured condition, for random-coil polyvinylpyrrolidone conjugates show a large shifts in pKa. In all cases examined, urea abolishes the masking of the conjugated dye by the protein or polymer. The dependence of ΔpKa on molecular weight of the protein as well as the effects of urea have been interpreted in terms of the participation of ordered water (hydrotactoids) in interaction between apolar groups.