摘要:

AbstractThe13C off‐resonance rotating frame spin‐lattice relaxation technique is applicable to the study of protien rotational diffusion behaviour in a variety of experimental situations. The original formalism of James and co‐workers (1978) (J. Amer. Chem. Soc.100, 3590–3594) was constrained by the assumption of random isotropic reorientational motion. Here we include in the formalism anisotropic tumbling, and present the results of computer simulations illustrating the differences between anisotropic and isotropic reorientational motion for the off‐resonance rotating frame spin–lattice relaxation experiment. In addition, We have included chemical shift anisotropy of the peptide carbonyl carbon as an additional relaxation mechanism contribution, to permit high field nmr protein rotational diffusion m

ISSN:0006-3525    

DOI:10.1002/bip.360290302

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

年代:1990

数据来源: WILEY

摘要:

AbstractBinding of chromomycin A3(CRA) to calf thymas DNA was investigated in the presence of divalent cations using visible absorption and1H‐nmr spectroscopies. An apparent equilibrium binding constant (∼ 1011M−1) was obtained from metal competition experiments using EDTA to remove the metal cation from the DNA–M–CRA (M: metal) complex. The large binding constant of the drug to DNA enabled us to obtain essentially complete complexation of CRA to the short homogeneous d(ATGCAT)2duplex using stoichiometric amounts of the metal cation. Large induced chemical shifts were observed in the1H‐nmr spectrum of the above complex using the paramagnetic Co2+cation indicating that the metal occupies a unique binding site. Since no induced1H‐nmr chemical shifts were observed for the drug–Co2+mixture, it was concluded that no metal–drug complex is formed. In addition, it was found that bound CRA is negatively charged at physiological pH and binding to the DNA could be affected only by using metal cations whose ionic radius size (<0.85 Å) and charge (2+) were simultaneously satisfied. Stringent metal cation selectivity for the DNA–M–CRA complex may be intimately connected with the antitumor selectivity of CRA, since different types of cells generally possess widely differing molar concentra

ISSN:0006-3525    

DOI:10.1002/bip.360290303

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

年代:1990

数据来源: WILEY

摘要:

AbstractBy combining electrophoresis with movements of fluorescence pattern after photobleaching (MOFPAP), which is abbreviated as EMOFPAP, we are able to measure electrophoretic mobilities of large DNA fragments in an agarose gel within a fairly short time scale (about 10 min or even down to 1 min). The new method represents a significant improvement in experiment time when compared with the time (typically on the order of hours) required to determine the average electrophoretic mobility of large DNA fragments in agarose gels by means of either conventional gel electrophoresis or pulsed‐field gel electrophoresis. In this article, we present the EMOFPAP experimental setup and consider optical conditions, including beam profile geometry and fluorescence pattern formation. A realistic formula that can explain the parameters governing the EMOFPAP method using our present optical setup has been derived. A comparison of results between experimental and computer simulation data is made, and an optimization of the EMOFPAP method is propose

ISSN:0006-3525    

DOI:10.1002/bip.360290304

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe13C off‐resonance rotating frame spin‐lattice relaxation technique is applicable to the study of protein rotational diffusion behavior in both model in vitro and in vivo systems. The original formalism of James and co‐workers [(1978)J. Am. Chem. Soc.100, 3590–3594] was constrained by the assumption of random isotropic reorientational motion of a monodisperse protein population. Here we extend the formalism to include polydispersity. Application is made to the alkaline pH induced association of lysozyme, lysozyme–bovine serum albumin mixtures, and to the phase separation of lysozyme salt–water mixtures induced by low

ISSN:0006-3525    

DOI:10.1002/bip.360290305

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe peptide N‐Boc‐L‐Pro‐dehydro‐Phe‐L‐Gly‐OH was synthesized by the usual workup procedure and finally coupling the N‐Boc‐L‐Pro‐dehydro‐Phe to glycine. The peptide crystallizes in monoclinic space group P21witha= 8.951(4) Å,b= 5.677 (6) Å,c= 21.192(11) Å, β = 96.97(4)°,V= 1069(1) Å3,Z= 2, dm= 1.295(5) Mgm−3, and dc= 1.297(4) Mgm−3. The structure was determined by direct methods using SHELXS86. The structure was refined by the block‐diagonal least‐squares procedure to anRvalue of 0.074 for 1002 observed reflections. The C 2α–C 2βdistance of 1.33(2) Å is an appropriate double bond length. The angle C 2α–C 2β–C 2γis 133(1)°. The peptide backbone torsion angles are θ1= −167(1)°, ω0= 179(1)°, ϕ1= −48(1)°, ψ1= 137(1)°, ω1= 175(1)°, ϕ2= 65(2)°, ψ2= 15(2)°, ω2= −179(1)°, and ϕ3= −166(1)°. These values show that the Boc group has atrans–transconformation while the peptide backbone adopts a β‐turn II conformation, which is stablized by an intramolecular hydrogen bond of length of 3.05(1) Å. The structures of dehydro‐Phe containing peptides suggest that the dehydro‐Phe promotes the β‐turn II conformation. The five‐membered pyrrolidine ring of the Pro residue adopts an ideal Cγ‐exoconformation with torsion angles χ 11= −24(1)°, χ 12= 34(1)°, χ 13= −30(1)°, χ 14= 15(1)°, and θ 10= 6(1)°. The side chain torsion angles in dehydro‐Phe are χ 21= −1(2)°, χ 22, 1= −176(1)°, and χ 22, 2= 8(2)°. The Plane of C 2α–C 2β–C 2γis rotated with respect to the plane of the phenyl ring at 7(1)°, which

ISSN:0006-3525    

DOI:10.1002/bip.360290306

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

年代:1990

数据来源: WILEY

摘要:

AbstractMolecular dynamics simulations on the sequence d(CGCGAATTCGCG)2have been carried out using both united atom and all‐atom representations, and starting the simulations both from a regular repeating B‐DNA structure and from the x‐ray single crystal B‐DNA structure. An all‐atom B‐DNA simulation on the sequence d(GCGCGCGCGC)2has also been carried out, in order to compare it with a previous united atom simulation. The helix repeats, H‐bonding, sugar pucker profiles, and average torsional angles are all in the range observed in crystallographic and nmr studies for B‐DNA helices. In some of the sequences, there is a significant bend in the DNA helices. The individual helix repeats, with focus on 3′CpG5′ and 3′GpC5′ units, show the opposite helix repeat to that suggest

ISSN:0006-3525    

DOI:10.1002/bip.360290307

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

年代:1990

数据来源: WILEY

摘要:

AbstractDL‐ArginineDL‐glutamate monohydrate andDL‐arginineDL‐aspartate, the firstDL‐DLamino acid–amino acid complexes to be prepared and x‐ray analyzed, crystallize in the space group P1witha= 5.139(2),b= 10.620(1),c= 14.473(2) Å, α = 101.34(1)°, β = 94.08(2)°, γ = 91.38(2)° anda= 5.402(3),b= 9.933(3),c= 13.881(2) Å, α = 99.24(2)°, β = 99.73(3)°, γ = 97.28(3)°, respectively. The structures were solved using counter data and refined toRvalues of 0.050 and 0.077 for 1827 and 1739 observed reflections, respectively. The basic element of aggregation in both structures is an infinite chain made up of pairs of molecules. Each pair, consisting of aL‐ and aD‐isomer, is stabilized by two centrosymmetrically or nearly centrosymmetrically related hydrogen bonds involving the α‐amino and the α‐carboxylate groups. Adjacent pairs in the chain are then connected by specific guanidyl–carboxylate interactions. The infinite chains are interconnected through hydrogen bonds to form molecular sheets. The sheets are then stacked along the shortest cell translation. The interactions between sheets involve two head‐to‐tail sequences in the glutamate complex and one such sequence in the aspartate complex. However, unlike in the correspondingLLandDLcomplexes, head‐to‐tail sequences are not the central feature of molecular aggregation in theDL‐DLcomplexes. Indeed, fundamental differences exist among the aggregatio

ISSN:0006-3525    

DOI:10.1002/bip.360290308

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

年代:1990

数据来源: WILEY

摘要:

AbstractA fast Monte Carlo integration algorithm with varying time step is described for cooperative binding of ligands of arbitrary length to a one‐dimensional lattice. This algorithm is particularly suitable for strongly cooperative or anticooperative systems, i.e., when the time scales for different kinetic events are very different. As an application, the kinetics of a bimodal two‐ligand system are briefly discus

ISSN:0006-3525    

DOI:10.1002/bip.360290309

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe preparation of copolypeptides consisting ofL‐aspartic acid andL‐glutamic acid was performed to determine the effects of copolymer composition and sequential distributions on the rate of degradation by papain in a PECF (pseudoextracellular fluid) at pH 4.75 and 7.40, at 37.0°C, to simulatein vivopolymer degradation. Random copolymers consisting of β‐benzylL‐aspartate and γ‐benzylL‐glutamate were synthesized by the N‐carboxyanhydride method. Water‐soluble copolymers were obtained by successive reactions of side chains by anhydrous HBr treatment. All the samples were found to be degraded by random chain scission with papain. Further, the degradation data for the samples followed the Michaelis–Menten rate law, being the first order in papain concentration. The nature of side chains are important to the rate of degradation by papain and it was controlled by the comonomer composition as well as the sequential distribution of comonomers in

ISSN:0006-3525    

DOI:10.1002/bip.360290310

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe elastic modulus (G′) of factor XIIIa induced fibrinogen gels was found to be substantially lower than theG′ of fibrin gels that were formed by clotting fibrinogen with thrombin. The addition of fibronectin and/or the reducing reagent dithiothreitol (DTT) to the factor XIIIa coagulation mixture led to the formation of a weaker gel structure, while the rigidity of thrombin induced clots was not appreciably affected by the inclusion of the DTT but increased somewhat in the presence of fibronectin. The reasons for the differing clot rigidities are discussed in terms of biochemical mechani

ISSN:0006-3525    

DOI:10.1002/bip.360290311

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

年代:1990

数据来源: WILEY