Radioprotective effect of polyethylene glycol

Polyethylene glycol of molecular weight 400 (PEG-400) had a radioprotective effect of about 20% against lethality when given ip 20 min prior to single or fractionated X-ray doses to the head and neck. Dose modification factors (DMF) based on LD50/15 values ranged from 1.14 to 1.24. A similar DMF of 1.12 based on LD50/30 values was obtained using single doses of whole-body X irradiation. Mice given head and neck irradiation had significantly reduced rectal temperatures (31.3 +/- 3.0 degrees C) 9 days post irradiation compared with unirradiated controls (35.4 +/- 0.6 degrees C). No such reduction was observed when PEG-400 was given with radiation (36.3 +/- 0.9 degrees C). PEG-400 also lessened, but not significantly, the frequency of shivering in irradiated animals. Histopathologic examination of the oral structures demonstrated only marginal protection by PEG-400. Estimation of the alpha/beta ratio from LD50 data on head and neck-irradiated mice yielded values of 4.4 +/- 1.9 (95% confidence limits) Gy without PEG-400 and 7.9 +/- 1.4 Gy with PEG-400. Since it is a non-thiol radioprotector, PEG-400 may be more useful when combined with more conventional thiol-containing radioprotectors.     

Effects of polyethylene glycol on stability of alpha-chymotrypsin in aqueous ethanol solvent

The effects of polyethylene glycol (PEG) of different molecular weights (400, 2000, 6000, 12,000, 20,000, and 35,000) on the conformational stability and catalytic activity of alpha-chymotrypsin in 60% ethanol were studied. The inactivation caused by the organic solvent was not influenced by PEG 400. However, the PEGs with higher molecular weights up to 35,000 increased the stability of the enzyme, but this alpha-chymotrypsin stabilizing effect was molecular weight-independent. With increase of the molecular weight of PEG, a more stable tertiary structure of the enzyme was observed.     

Molecular mechanism of polyethylene glycol mediated stabilization of protein

The effect of different molar ratios of polyethylene glycol (PEG) on the conformational stability of protein, bovine serum albumin (BSA), was studied. The binding of PEG with BSA was observed by fluorescence spectroscopy by measuring the fluorescence intensity after displacement of PEG with chromophore ANS and had further been confirmed by measuring the intrinsic fluorescence of tryptophan residues of BSA. Co-lyophilization of BSA with PEG at optimum BSA:PEG molar ratio led to the formation of the stable protein particles. Circular dichroism (CD) spectroscopy study suggested that a conformational change had occurred in the protein after PEG interaction and demonstrated the highest stability of protein at the optimum BSA:PEG molar ratio of 1:0.75. Additional differential scanning calorimetry (DSC) study suggested strong binding of PEG to protein leading to thermal stability at optimum molar ratio. Molecular mechanism operating behind the polyethylene glycol (PEG) mediated stabilization of the protein suggested that strong physical adsorption of PEG on the hydrophobic core of the protein (BSA) along with surface adsorption led to the stability of protein.     

Universal polyethylene glycol linkers for attaching receptor ligands to quantum dots

Biologically active small molecule derivatives that can be conjugated to quantum dots have the promise of revolutionizing fluorescent imaging in biology. In order to achieve this several technical hurdles have to be surmounted, one of which is non-specific adsorption of quantum dots to cell membranes. Pegylating quantum dots has been shown to eliminate non-specific binding. Consequently it is necessary to develop a universal synthetic methodology to attach small molecule ligands to polyethylene glycol. These pegylated small molecules may then be conjugated to the surfaces of quantum dots. Ideally this universal strategy should be adaptable and be applicable to PEG chains of varying lengths. This paper describes the development of one such methodology and the synthesis of a pegylated derivative of the known 5HT₂ agonist 1-(2-aminopropyl)-2,5-dimethoxy benzene. This compound was tested and found to be an agonist for the 5HT_2A and 5HT_2C receptor having EC₅₀ values of 250 and 50 nM, respectively.     

Enhancement effect of polyethylene glycol on enzymatic synthesis of cephalexin

In an enzymatic synthesis of cephalexin (CEX) using an acylase from Xanthomonas citri, the effect of polyethylene glycol (PEG) on the synthetic reaction of 7-amino-3-deacetoxycephalosporanic acid (7-ADCA) and D-alpha-phenyl-glycine methyl ester (PGM) to CEX was investigated. The addition of PEG (MW 300-20,000) increased the yield significantly. This yield enhancement effect tended to increase with the increasing molecular weight of PEG. Addition of PEG to the reaction system did not affect both the CEX and PGM hydrolytic reactions. The PEG added to the reaction medium used in these experiments did not depress the water activity significantly, and the product yield improvement could not be explained by the activity alone. The PEG stabilized the enzyme activity to some extent, but this stabilizing effect was only partially attributable to the yield enhancement of CEX. The enhancing effect of PEG on the synthetic yield increased with the increasing PEG molecular weight or the length of the poly(oxy-1,2-ethanediyl) chain, which increases the hydrophobicity of PEG. This finding consequently has led to the conclusion that the PEG structure renders the affinity between enzyme and 7-ADCA, which is a hydrophobic substrate. The microenvironmental hydrophobicity of PEG and its interaction with the hydrophobic substrate was found to be the main reason for the improvement of the CEX yield. In fact, the Michaelis-Menten kinetic constant for 7-ADCA, K(7-ADCA) in the presence of PEG was smaller than that in the control system (without PEG addition). (c) 1993 John Wiley & Sons, Inc.     

重组L-门冬酰胺酶工程菌的表达和PEG的化学修饰

目的提高重组L-门冬酰胺酶(rL-ASP)工程菌的表达量,分离纯化rL-ASP并对之进行PEG化学修饰。方法将带有编码rL-ASP的基因的质粒(pKA)导入不同的宿主菌中,挑出高表达菌株,同时优化发酵培养基,分离纯化获得的高纯度rL-ASP再用PEG进行化学修饰,SDS-PAGE检测修饰效果。结果在pH7.0的条件下,宿主菌为JMl09的工程菌pKA/JMl09酶活力最高,三角瓶振摇培养的酶活力可达216×103IU/L;发酵罐发酵培养,酶活力达312×103IU/L。纯化后的rL-ASP比活力为220IU/mg,rL-ASP经过PEG化学修饰生成rL-ASP-PEG,分子量发生改变。结论改变目标蛋白表达的宿主菌和优化发酵工艺,提高了rL-ASP的表达量,纯化的rL-ASP经过PEG化学修饰后分子量增大。     

Molecular dynamics studies of polyethylene oxide and polyethylene glycol: hydrodynamic radius and shape anisotropy

A revision (C35r) to the CHARMM ether force field is shown to reproduce experimentally observed conformational populations of dimethoxyethane. Molecular dynamics simulations of 9, 18, 27, and 36-mers of polyethylene oxide (PEO) and 27-mers of polyethylene glycol (PEG) in water based on C35r yield a persistence length λ = 3.7 Å, in quantitative agreement with experimentally obtained values of 3.7 Å for PEO and 3.8 Å for PEG; agreement with experimental values for hydrodynamic radii of comparably sized PEG is also excellent. The exponent υ relating the radius of gyration and molecular weight of PEO from the simulations equals 0.515 ± 0.023, consistent with experimental observations that low molecular weight PEG behaves as an ideal chain. The shape anisotropy of hydrated PEO is 2.59:1.44:1.00. The dimension of the middle length for each of the polymers nearly equals the hydrodynamic radius R_h obtained from diffusion measurements in solution. This explains the correspondence of R_h and R_p, the pore radius of membrane channels: a polymer such as PEG diffuses with its long axis parallel to the membrane channel, and passes through the channel without substantial distortion.     

Molecular dynamics of anthraquinone DNA intercalators with polyethylene glycol side chains

The interactions of a homologous series of four anthraquinone (AQ) intercalators with increasing lengths of polyethylene glycol (PEG) side chains with DNA have been studied via molecular dynamics (MD) simulations. The geometry, conformation, interactions, and hydration of the complexes were examined. The geometries of the four ligands were similar with parallel stacking to the long axis of the adjacent DNA base pairs. Hydrogen bonding between the AQ amide and DNA led to a preference for the trans-syn conformer. As the side chain lengthened, binding to DNA reduced the conformational space, resulting in an increase in unfavorable entropy. Increased localization of the PEG side chain in the DNA groove, indicating some interaction of the side chain with DNA, also contributed unfavorably to the entropy. The changes in free energy of binding due to entropic considerations (-3.9 to -6.3 kcal/mol) of AQ I-IV were significant. The hydration of the PEG side chain decreased upon binding to DNA. Understanding of side chain conformations, interactions, and hydration changes that accompany the formation of a ligand-DNA complex may be important in the development of new applications of pegylated small molecules that target biological macromolecules.     

New hydrogel based on polyethylene glycol cross-linked with bovine serum albumin

Summary A new and rapid method for preparing a protaneous-polymeric hydrogel is described. The gel matrix is obtained by covalent cross-linking between preactivated polyethylene glycol of 3350 molecular mass and bovine serum albumin in aqueous solution at basic pH. The polyethylene glycol-albumin hydrogel showed high protein retention and a very good swelling capacity.     

Molecular assembly of CuBrSe3 in ethylene glycol solvent

CuBrSe₃ has been synthesized by the reaction between CuBr₂ and Se in ethylene glycol (EG) solvent at 100 °C. In the process, CuBr₂ was reduced to brom-complexes of Cu(I), such as , the complexes participated in the reaction as intermediates. Based on experimental results and the structure characterization of CuBrSe₃ crystal, a possible mechanism for CuBrSe₃ formation was proposed. The mechanism suggests that Se chains assembly with the brom-complexes of Cu(I) to form CuBr helical chains, and then CuBrSe₃ crystal.     

Stabilization of a supplemental digestive enzyme by post-translational engineering using chemically-activated polyethylene glycol

Many enzymes used as digestive aids exhibit, at best, moderate stability when incubated under gastrointestinal conditions. A supplemental β-galactosidase administered orally to treat lactose intolerance was conjugated to 40 kDa, branched polyethylene glycol (PEG). PEGylation increased the enzyme's relative activity at lower pH values (2.5-4.5) and doubled enzyme stability at pH 2.5. The PEGylated enzyme retained significantly more residual activity after exposure to simulated gastric conditions (52% versus 31%), a consequence of protection from both pepsin and low pH mediated inactivation. Conjugation also provided significant protection against the proteolytic component of pancreatin. Overall, the PEGylated enzyme retained over twice the levels of residual activity recorded for non-PEGylated enzyme after exposure to complete simulated gastrointestinal conditions. PEGylation also marginally improved the enzyme's kinetic characteristics. When using its physiological substrate (lactose), K(m) values recorded were slightly decreased (from 83 to 60 μM) and k(cat)/K(m) values (M(-1) s(-1)) were increased from 100 to 147. This appears to be the first report of the use of a conjugated PEG to stabilize a digestive enzyme and the first report of the ability of conjugated PEG to stabilize a protein at low pH.     

聚乙二醇对东北红豆杉培养细胞的

在改良的B     

Differential effect of sorbitol and polyethylene glycol on antioxidant enzymes in rice leaves

Polyethylene glycol (PEG) and sorbitol (ST) have each been used inosmotically induced water stress studies in plants, however, these osmotica maynot have equivalent effects in plants. The present study was designed to examinewhether antioxidant enzyme responses in rice leaves are different for PEG and STof osmotic potential –1.5 MPa. As judged by relative watercontent, PEG treatment resulted in a higher degree of water stress in riceleaves than ST treatment. PEG treatment markedly increased lipid peroxidation,judged by malondialdehyde content, in rice leaves. However, ST treatment had noeffect on lipid peroxidation. An increase in peroxidase (POX), ascorbateperoxidase (APX) and glutathione reductase (GR) activities was observed in riceleaves treated with ST. PEG treatment had no effect on POX and APX activitiesand decreased GR activity in rice leaves. The decrease in superoxide dismutaseactivity induced by PEG was more pronounced than by ST. Cycloheximide blockedthe enhanced activities of POX, APX and GR by ST, indicating de novo synthesisof the enzymes. Results suggest that ST but not PEG treatment can up-regulateantioxidant system in rice leaves.     

Inducible or constitutive polyethylene glycol dehydrogenase involved in the aerobic metabolism of polyethylene glycol

2, 6-Dichlorophenolindophenol (DCIP)-dependent polyethylene glycol (PEG) dehydrogenase activity was found in the particulate fractions of cell-free extracts prepared from PEG-utilizing bacteria (Pseudomonas and Flavobacterium species). This result suggested that PEG dehydrogenase is linked to the respiratory chain of each bacterium and that the enzyme plays a major role in the aerobic metabolism of PEG. Enzyme activities were strongly inhibited by 1, 4-benzoquinone. No metal ion was indispensable for the enzyme activities. Enzyme activities of PEG-utilizing bacteria were induced by PEG except for the activity of PEG 4000-utilizing Flavobacterium sp. no. 203 which had a constitutive enzyme. Although PEG-utilizing bacteria had different growth substrate specificities toward PEGs 200–20,000, their PEG dehydrogenases oxidized the same molecular wt. range of PEGs (dimer-20,000). Cell-free extracts of PEG 400-, 1000- or 4000-utilizing bacteria oxidized PEG 6000 and 20,000 though these bigger PEGs could not be utilized as the sole carbon and energy sources by the bacteria. Methanol, ethylene glycol and glycerol were not or only barely dehydrogenated by all the enzyme preparations.     

聚乙二醇对PEG化重组人促红细胞生成素热稳定性和生物学活性的影响

为了研究聚乙二醇对PEG化rhEPO热稳定性和生物学活性的影响,用酶学方法切除rhEPO和PEGrhEPO分子中的N连接糖基,研究酶切产物在37℃时287nm和350nm吸光度随时间的变化;用MTT比色法,网织红细胞法和HCT法比较体内和体外生物学活性的改变。结果显示聚乙二醇修饰能显著减少无N连接糖基的rhEPO分子间的聚集,降低rhEPO体外生物学活性,但增高体内生物学活性;无N连接糖基的PEG化rhEPO具有与rhEPO相当的体内生物学活性。因此聚乙二醇能提高rhEPO热稳定性;聚乙二醇可替代糖基,维持rhEPO的体内生物学活性。用PEG修饰原核细胞表达的rhEPO是开发rhEPO制品的新思路。     

Purification and characterization of polyethylene glycol dehydrogenase involved in the bacterial metabolism of polyethylene glycol

Polyethylene glycol (PEG) dehydrogenase in crude extracts of a PEG 20,000-utilizing mixed culture was purified 24 times by precipitation with ammonium sulfate, solubilization with laurylbetaine, and chromatography with diethylamino-ethyl-cellulose, hydroxylapatite, and Sephadex G-200. The purified enzyme was confirmed to be homogeneous by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular weight of the enzyme, which appeared to consist of four identical subunits, was 2.4 X 10(5). The enzyme was stable below 35 degrees C and in the pH range of 7.5 to 9.0. The optimum pH and temperature of the activity were around 8.0 and 60 degrees C, respectively. The enzyme did not require any metal ions for activity and oxidized various kinds of PEGs, among which PEG 6,000 was the most active substrate. The apparent Km values for tetraethylene glycol and PEG 6,000 were about 10.0 and 3.0 mM, respectively.     

Chemically defined polyethylene glycol siRNA conjugates with enhanced gene silencing effect

The therapeutic application of siRNA suffers from poor bioavailability caused by rapid degradation and elimination. The covalent attachment of PEG is a universal concept to increase molecular size and enhance the pharmacokinetic properties of biomacromolecules. We devised a facile approach for attachment of PEG molecules with a defined molecular weight, and successful purification of the resulting conjugates. We directly conjugated structurally defined PEG chains with twelve ethylene glycol units to the 3′-terminal hydroxyl group of both sense and antisense strands via an aminoalkyl linker. The conjugates were easily purified by HPLC and successful PEGylation and molecule integrity were confirmed by ESI-MS. The evaluation of in vitro gene knockdown of two different targets in MCF-7 breast cancer cells showed stable pharmacologic activity when combined with a standard transfection reagent. Sense strand PEGylation even increased the silencing potency of a CRCX4-siRNA which had modest activity in its wild-type form. The results indicate that PEG chains at the 3′-terminus of both strands of siRNA are well tolerated by the RNAi effector. The attachment of short, chemically defined PEG chains is a feasible approach to improve the pharmacokinetic properties of siRNA, and can be combined with other targeted and untargeted delivery vehicles.     

Protein precipitation by polyethylene glycol: a generalized model based on hydrodynamic radius

PEGs for protein precipitation are usually classified by molecular weight. The higher molecular weight precipitants are more efficient but result in higher viscosity. Following empirical evidence that the precipitation efficiency is more comprehensively characterized by PEG hydrodynamic radius (r_h,PEG) than molecular weight, this paper proposes a model to explicate the significance of r_h,PEG. A general expression was formulated to characterize the PEG effect exclusively by r_h,PEG. The coefficients of a linearized form were then fitted using empirical solubility data. The result is a simple numerical relation that models the efficiency of general-shaped PEG precipitants as a function of r_h,PEG and protein hydrodynamic radius (r_h,prot). This equation also explains the effects of environmental conditions and PEG branching. While predictions by the proposed correlation agree reasonably well with independent solubility data, its simplicity gives rise to potential quantitative deviations when involving small proteins, large proteins and protein mixtures. Nonetheless, the model offers a new insight into the precipitation mechanism by clarifying the significance of r_h,PEG. This in turn helps to refine the selection criterion for PEG precipitants.     

Effect of ethylene glycol and polyethylene glycol on the acid-unfolded state of trypsinogen

Effect of increasing concentrations of two of the polyols, ethylene glycol (EG) and polyethylene glycol (PEG), was studied by near and far circular dichroism (CD), fluorescence emission spectroscopy, and binding of hydrophobic dye, 1-anilino-8-naphthalene sulfonic acid (ANS). Far-UV CD spectra show the transition of acid-unfolded trypsinogen from an unordered state to an intermediate state having ordered secondary structure. Interestingly, near-UV CD spectra show some amounts of stabilizing effect on the tertiary structure of the protein also. Tryptophan fluorescence studies indicate the change in the environment of the tryptophan residues on addition of EG and PEG. Maximum ANS binding occurs in presence of 80% EG and 90% PEG (v/v), suggesting the presence of an intermediate or molten globule-like state at high concentrations of the two polyols.