摘要:

AbstractThe first observation of ir vibrational CD (VCD) in small model DNA molecules is reported. The VCD signals in the 1550–1750‐cm−1spectral region, which originate from coupling of carbonyl stretching modes of the nucleic acid bases, are found to be sensitive to the handedness of the polymer helix.The formalism to calculate VCD intensities of polymers is developed from the exciton model derived earlier by Tinoco [(1963)Radiation Res.20, 133; (1960)J. Chem. Phys.33, 1332; (1964)J. Am. Chem. Soc.86, 297] and Schellman and co‐workers [(1975)Biopolymers14, 173; (1969)J. Phys. Chem.73, 28]. The resulting equations, which are a direct extension of the dimeric case known as the “coupled oscillator,” are used in model calculations of the helic

ISSN:0006-3525    

DOI:10.1002/bip.360281202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractIn Monte Carlo simulations of polymeric chains, the chains, the chains are most often represented as spheres, or cylinders with flat ends. In this methodological paper, we adopt a representation of the chains as spherocylinders (continuous cylinders ending in semispheres). With such a representation the testing for chain overlap, which is the crucial step for the incluson of the excluded volume effect in the simulations, can be defined in a rigorous geometrical framework. The treatment we then derive fulfills the following features:—it allows a very simple, automatic, and exhaustive calsificatim of all the possible configurations;—it provides a physical representation for steric hindrance effects more natural than the flat‐ended cylinders. Notably, this representation avoids the introduction of artificial anisotropies in the treatments.This spherocylindrical representation is also well suited for several types of calculations that can be involved in elaborate Monte Carlo simula

ISSN:0006-3525    

DOI:10.1002/bip.360281203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractPyridoxylated normal adult human hemoglobin (HbAo) has been prepared using both oxygenated and deoxygenated HbAo at pH 6.8 and room temperature without the addition of Tris to produce a mixture with P50of 30 ± 2 torr and a Hill coefficient of 2.3 ± 0.1 similar to that of the isolated adult human hemoglobin from the red blood cell. Reduction of the pyridoxylated HbAo in the oxygen‐ligated form by sodium borohydride gives unacceptable levels of methemoglobin (i.e.,>10%). Exessive foaming and methemoglobin formation can be partially avoided using deoxyHbAo. Reduction with sodium cyanoborohydride is much gentler and gives solutions with<5% methemoglobin. Both reducing agents give products with multiple components as shown by analytical chromatography. Radioautography on the isoelectric focusing gels of HbAo treated with14C pyridoxal 5‐phosphate (PLP) shows three major bands for the cyanoborohydride‐reduced derivatives and a much more complex mixture of labeled molecules after the sodium borohydride reduction. When pyridoxylated hemoglobin is prepared without reduction, the preparation, after passage through a mixed‐bed resin, contains 0.4 equivalents of PLP per heme, and has a P50of 30 ± 2 torr and annvalue of 2.3 similar to the values found after reduction. Upon anion exchange resin chromatography, the PLP is removed, indicating that the reaction forms a reversible Schiff base. On standing at 4°C for one month, this preparation produces a mixture of HbAo and pyridoxylated HbAo with the original P50. Methemoglobin increased to 3% during this incubation. After four months in the cold, the yield of a single chromatographic species is 70% with 20% methemoglobin. This fraction appears to be stable and can be passed through an anion exchange column without release of the PLP. Separation of the individual chains by reverse‐phase chromatography indicates that the addition of PLP to HbAo is directed solely to the β‐chains. This is also the case for the cyanoborohydride reduced derivatives. When NaBH4is used for the reduction, radioactively labeled PLP is found on both the

ISSN:0006-3525    

DOI:10.1002/bip.360281204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe molecular dynamics (MD) simulation of superoxide dismutase (SOD) in water is carried out for a total of 23 ps. The simulation system is a 26 Å sphere centered at the active site of SOD, including 1602 atoms from SOD and 1761 water molecules. There is no gross deviation from the x‐ray structure for the average MD structure. The structure and potential fluctuations around the active site are examined. The results provide new insight to the interactions between SOD and its substrate superoxi

ISSN:0006-3525    

DOI:10.1002/bip.360281205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe structure of the complex formed between the 7H‐pyridocarbazole monomer [{(2‐piperidyl)‐2,1‐ethane‐y1} {10‐methoxy‐7H‐pyrido[4,3‐c]carbazolium} dimethane sulfonate]and the autocomplementary hexanucleotide d(CpGpApTpCpG)2in aqueous solution is analyzed by 270‐ and 400‐MHz1H‐nmr. The large upfield shifts observed for both the drug and the self‐complementary hexanucleotide protons provide evidence for intercalated complexes. The observation of intermolecular nuclear Overhauser effects between drug and the hexanucleotide protons gives a privileged orientation of the durg in the intercalation site with the quaternarizing ethyl piperidine chain protruding in the major groove. Moreover, the data suggest an intercalation based on the neighbor exclusion site principle in the th

ISSN:0006-3525    

DOI:10.1002/bip.360281206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe structure of the complex formed in aqueous solution between ditercalinium, a bisintercalating drug, and the self‐complementary hexanucleotide d(CpGpApTpCpG)2is investigated by 400‐MHz1H‐nmr and 162‐MHz31P‐nmr. Whatever the drug to thlix ratio, ditercaliniun occurred in the bound form, whereas free and complexed hexanucleotide and are in slow exchange. This allows unambiguous resonance assignm, ent through two‐dimensional chemical exvhange experiments. The strong upfield shifts measured on most aromatic protons on both drug and bases as well as on DNA imino protons are consistent with bisintercalation of the dimer. Nuclear Overhauser effects observed between drug and nucleeotide protons give a defined geometry for complexation, and suggest a DNA conformational change upon d

ISSN:0006-3525    

DOI:10.1002/bip.360281207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe thermal unfolding of myosin rod, light meromyosin (LMM), and myosin subfragment 2 (S‐2) was studied by differential scanning calorimetry (DSC) over the pH range of 6.5–9.0 in 0.5MKCl and either 0.20Msodium phosphate or 0.15Msodium pyrophosphate. Two rod samples were examined: one was purified by Sephadex G‐200 without prior denaturation (native rod), and the other was purified by a cycle of denaturation‐renaturation followed by Sephacryl S‐200 chromatography (renatured rod). There were clearly distinguishable differences in the calorimetric behavior of these two samples. At pH 7.0 in phosphate the DSC curves of native rod were deconvoluted into six endothermic two‐state transitions with melting temperatures in the range of 46–67°C and a total enthalpy of 4346 kJ/mol. Under identical conditions the melting profile of LMM was resolved into five endothermic peaks with transition temperatures in the range of 45–66°C, and the thermal profile of long S‐2 was resolved into two endotherms, 46 and 57°C. Transition 4 observed with native rod was present in the deconvoluted DSC curve for long S‐2, but absent in the DSC curve for LMM. This transition was identified with the high‐temperature transition detected with long S‐2 and attributed to the melting of the coiled‐coil α‐helical segment of subfragment 2 (short S‐2). The low‐temperature transition of long S‐2 was attributed to the unfolding of the hinge region. The smallest transition temperatures observed for all three fragments were 45–46°C. It is suggested that the most unstable domain in rod (domain 1) responsible for the 46°C transition includes both the hinge region, which is the C‐terminal segment of long S‐2, and a short N‐terminal segment of LMM. This domain, accounting for 21% of the rod structure, contains the S‐2/LMM junction, and upon proteolytic cleavage yields the C‐terminal and N‐terminal ends of long S‐2 and LMM, respectively. Over the pH range of 6.5–7.5, the observed specific heat of denaturation of rod was approximately equal to the sum of the specific heats of LMM and S‐2. This finding provides an additional argu

ISSN:0006-3525    

DOI:10.1002/bip.360281208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractA study of the monomeric chromophore of the oligopeptides netropsin (1), distamycin III (2), and distamycin V (3) by polarization spectroscopy techniques1and molecular orbital calculations is reported. Linear dichroism spectra of the monomeric model compounds 1‐methyl‐2(ethylcarbamoyl)‐4‐acetamido‐pyrrole (4) and 1‐methyl‐2(ethylcarbamoyl)‐pyrrole (5) dissolved and oriented in lyotropic and thermotropic liquid crystals provide, together with the magnetic CD spectra, experimental checks of the theoretical calculations. The polarization directions of the investigated transition obtained by these means in this study allow us to build up in the following paper2the exciton states of (1)‐(3) and these provide a stereochemical interpretation of the flow linear dichroism spectra of the complexes of DNA

ISSN:0006-3525    

DOI:10.1002/bip.360281209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe study of the monomeric chromophore of the distamycins reported in Ref. 1 was used here to build up a description of the electronic states of the whole oligopeptide by the exciton theory. Liquid crystal–linear dichroism (LC–LD) spectra of the distamycins were recorded by using as orienting solvents both thermotropic and lyotropic mesomorphic media. The agreement between the LD spectra and the polarization assignments by the exciton treatment is satisfactory. On this basis the flow‐LD spectra of the complex between distamycin V and DNA was interpreted in terms of the preferred relative orientations of the guest and host molecules. A single site location of the distamycin within the minor groove does not perfectly match the experimental order parameters. This orientational distribution function could be too simple to explain the experimental data. It may therefore be assumed that a small fraction of the guest molecules are preferentially aligned more parallel to the host chain axis than the minor groove. Alternatively, and probably more likely, the partial mismatch of the experimental data with the minor groove location may be seen as a manifestation of the well‐known stiffening and bending effects at the binding sites, which have already been observed by other tec

ISSN:0006-3525    

DOI:10.1002/bip.360281210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractA number of chemically modified hemoglobin preparations have been proposed for use as an emergency resuscitation fluid. The purpose for forming these hemoglobin derivatives is to decrease the oxygen binding (i.e., to increase the P50) and to increase the intravascular retention time. These goals have been met with various degrees of success by using the reaction with pyridoxyl 5‐phosphate to raise the P50, followed by the addition of glutaraldehyde to increase circulating half‐life by polymerization.1,2Other derivatives have been formed with polyethylene glycol,3,4bis‐(3,5‐dibromosalicyl) fumarate,5,6glycolaldehyde,7and 2‐nor‐2‐formylpyridoxal 5‐phosphate,8,9as well as with other compounds. All these derivatives introduce a foreign molecule into the hemoglobin, which may not always be desirable. Recently Tharp and Day10used cyanogen to form intersubunit amide cross‐links in hemoglobin without the incorporation of cyanogen. This approach is attractive if the appropriate functional properties can be attained. Takeda et al.11showed that equimolar concentrations of amino acids and disuccinimidyloxalate could form peptide bonds in high yield. We report the characteristics of the hemoglobin molecule modified by internal covalent amide bonds, which may be a suitable candidate for a re

ISSN:0006-3525    

DOI:10.1002/bip.360281211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY