摘要:

AbstractThe arginine and lysine residues of calf thymus histone H1 were modified with large molar excesses of 2,3‐butanedione andO‐methylisourea, respectively. Kinetic study of the modification reaction of the arginine residue revealed that the reaction is divided into the two pseudo‐first‐order processes. About a third (1 Arg) of the total arginine residues of the H1 molecule was rapidly modified without causing any detectable structural change of the molecule, and the slow modification of the remaining arginine residues (2 Arg) led to a loss of the folded structure of H1. In the case of lysine residue modification, 93% (56 Lys) of the total lysine residues of the H1 was modified with the same rate constant, while 7% (4 Lys) of lysine residue remained unmodified. When the reaction was performed in the presence of 6Mguanidine‐HCl, all of lysine residues were modified. It is concluded that the 2 arginine and 4 lysine residues resistant to modification are buried in interior regions of the H1 molecule and play an important role in the formation of the H1 globular structure, while the other 1 arginine and 56 lysine residues are exposed t

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200602

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe gel filtration method was applied to the study of the interaction of the metachromatic cationic dye methylene blue (MB) with heparin in aqueous solution. This method requires the determination of the total MB concentration in the effluent. It was found that (i) MB in aqueous solution can be extracted quantitatively with benzyl alcohol (BzlOH), (ii) the metachromatic effect of MB is not observed in BzlOH, and (iii) the presence of heparin in aqueous solution does not interfere in the BzlOH extraction of MB. Accurate determination of MB concentration in the effluent can be made by extraction of MB with BzlOH, followed by the usual absorption spectroscopy. In addition, the use of the spectrophotometric method with this procedure entailed no serious problem relating to adsorption of MB on the glass walls. Gel filtration binding experiments were successfully carried out on a Sephadex LH‐20 column using 0.005Macetate buffer as effluent. The binding data obtained were analyzed in terms of the cooperativity parameter according to the method of Schwarz. The thermodynamic parameters for the binding process of MB were also evaluated. It is shown that the binding of MB to heparin is highly cooperative, exothermic, and stabilized by entropic factor

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200603

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe synthesis of the tetrapeptide benzyloxycarbonyl(α‐aminoisobutyryl‐L‐prolyl)2‐methyl ester (Z‐(Aib‐Pro)2‐OMe) and an analysis of its conformation in solution and the solid state are reported. Stepwise synthesis using dicyclohexylcarbodiimide leads to racemization at Pro(2). Evidence for the presence of diastereomeric tetrapeptides is obtained from 270‐MHz1H‐nmr and 67.89‐MHz13C‐nmr. The all‐Ltetrapeptide is obtained by fractional crystallization from ethyl acetate. The NH of Aib(3) is shown to be involved in an intramo‐lecular hydrogen bond by variable‐temperature1H‐nmr and the solvent dependence of NH chemical shifts. The results are consistent with a β‐turn conformation with Aib(1) and Pro(2) at the corners stabilized by a 4 → 1 hydrogen bond. The molecule crystallizes in the space groupP212121, witha= 8.839,b= 14.938, andc= 22.015 Å. The structure has been refined to anRvalue of 0.051. The peptide backbone is all‐trans, and a 4 → 1 hydrogen bond, between the CO group of the urethane moiety and Aib(3) NH, is observed. Aib(1) and Pro(2) occupy the corner positions of a type I β‐turn with ϕ = −55.4°, Ψ = −31.3° for Aib(1) and ϕ = −71.6°, Ψ = −38° for Pro(2). The tertiary amide unit linking Pro(2) and Ai

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200604

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe synthesis of the octapeptide, benzyloxycarbonyl‐(α‐aminoisobutyryl‐L‐prolyl)4‐methyl ester [Z‐(Aib‐Pro)4‐OMe] and an analysis of its solution conformation is reported. The octapeptide is shown to possess three strong intramolecular hydrogen bonds on the basis of studies of the solvent and temperature dependence of NH chemical shifts and rates of hydrogen–deuterium exchange.13C studies are consistent with a structure involving onlytransAib‐Pro bonds, while ir experiments support a hydrogen‐bonded conformation. The Aib 3, 5, and 7 NH groups are shown to participate in hydrogen bonding. A 310helical conformation compatible with the spectroscopic data is suggested. The proposed conformation consists of three type III β‐turns with Aib and Pro at the corners and stabilized by 4 → 1 in

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200605

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

年代:1981

数据来源: WILEY

摘要:

AbstractQuasielastic and static light‐scattering measurements were made on DNA isolated from chicken erythrocyte mononucleosomes as a function of ionic strength between 6 × 10−4and 1.0M. A transition from single‐exponential autocorrelation functions to markedly non‐single‐exponential decays was observed around 10−2Mionic strength and was accompanied by a large decrease in the excess light‐scattering intensity. Autocorrelation functions recorded below 10−2Msalt were well fit by the sum of two exponential relaxation which differed by as much as 100‐fold in time constants. Apparent diffusion coefficients for the fast and slow processes plateaued around 10−3Mwith numerical values approximately 10‐fold and 1/10, respectively, of the translational diffusion coefficient for mononucleosome DNA at high ionic strength. This behavior is similar to that observed with poly(L‐lysine), for which the slow decay has been associated with a transition to an extraordinary phase. The strong and complex salt dependence observed here illustrates potential difficulties in deriving structural information from scattering by polyio

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200606

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe thermal dissociation of DNA by five distinct local processes as outlined by Azbel [(1980)Biopolymers19, 61–80] is treated as a collection of two‐state substransitions. With the traditional expression for loop entropy and the assumption of a small, positive loop‐initiation enthalpy, explicit relationships between thermodynamic parameters are derived for all five processes. The effect of each process on subtransitional width, unit enthalpy, and melting temperature is estimated; the latter being in excellent agreement with that predicted by Azbel. Criteria proposed for the deconvolution of the oscillatory high‐resolution melting profiles exhibited by short, homogeneous DNAs [Yen&Blake (1980)Biopolymers19, 681–700] have been applied to profiles of SV40 fragment [Gabbarro‐Arpa et al. (1979)Nature280, 515–517] and ϕx174‐RF DNA at two ionic strengths [Vizard et al. (1978)275, 250–251] and indicate that dissociation of the strands proceeds as a series of local two‐state subtransitions of domains 200–300 base pairs in length. Although the obvious overlap of some subtransitions raises questions about resolution, most sections are very well resolved with the minimum number of subtransitions and yield values for the apparent van't Hoff enthalpy in excellent agreement with those expected by calorimetric measurements. The flexibility of such an approach, where the enthalpy is recognized explicitly as an adjustable parameter, is especially suited for the analysis of profiles from unkown DNA sequences, and for the evaluation of extraordinary variations in free energy, such as that associated with loop formation or that resulting from variations in the linear charge density

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200607

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

年代:1981

数据来源: WILEY

摘要:

AbstractWe have measured the solution and film vacuum ultraviolet circular dichroism of a series of acetylated glucans containing α‐ and β‐(1→3), (1→4), and (1→6) linkages. In addition to the 210‐nm band studied previously, we observe the entire π‐π* band near 190 nm; these bands are negative for all triacetates regardless of configuration and conformation. A band near 170 nm shows configurational sensitivity for (1→3)‐ and (1→6)‐linked polysaccharides. The band is positive for both (1→4)‐linked triacetates, but when cellulose triacetate is partially deacetylated, the 170‐nm band becomes negative, thus making the correlation complete. The positive 170‐nm band in cellulose triacetate films is more than an order of magnitude more intense than in any other case and, further, is accompanied by an equally large negative band near 153 nm, raising the possibility that the dichroism in the triacetate arises from strong excitonic interactions which are dis

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200608

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe molar Kerr constantsmK, molar refractionsmR, and dipole moments μ are reported for theN‐methylacetamides CX3CONHCH3(X = H, CH3, F. CI, Br) and acetamides CX3CONH2(X = H, F, Cl, Br). The components of the polarizability tensor α are deduced forN‐methylacetamide and acetamide on the basis of the bond additivity approximation. This α is found to be considerably more anisotropic than was indicated in previous determinations by other methods. The data forN‐methylacetamide were used to calculatemK, μ, and γ2(anisotropy squared) ofN‐acetyl‐N′‐methylglycine amide andN‐acetyl‐N′‐methyl‐alanine amide as functions of the torsional angles (ϕ,Ψ). The statistical mechanical averages ofmK, μ, and γ2were calculated from conformational energies obt

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200609

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe relationship between published vicinal proton–proton coupling constants and the pseudorotation properties of the pyrrolidine ring inL‐proline, 4‐hydroxy‐L‐proline, 4‐fluoro‐L‐proline, and several linear and cyclic model proline peptides is investigated. Compared to earlier studies, several important improvements are incorporated: (1) a new empirical generalization of the classical Karplus equation is utilized, which allows a valid correction for the effects of electronegativity and orientation of substitutents on3JHH; (2) an empirical correlation between proton–proton torsion angles and the pseudorotational parametersPand τmis derived; and (3) the best fit of the conformational parameters to the experimental coupling constants is obtained by means of a computerized iterative least‐squares procedure. Two pseudorotation ranges were considered, classified as type N (χ2positive sign) and type S (χ2negative sign). The conformational equilibrium is fully described in terms of four geometrical parameters (PN, τN,PS, τS) and the equilibrium constantK. The present results indicate that, in general, the geometrical properties found in x‐ray studies of proline and hydroxyproline residues are well preserved in solution. Several novel features are encountered, however. It is demonstrated that the proline ring occurs in a practically 1:1 conformational equilibrium between well‐defined N‐ and S‐type forms. Introduction of an amide group at the C‐terminal end has no observable effect on this equilibrium, but the formation of a peptide bond at the imino nitrogen site results in a pronounced, but not exclusive, preference for an S‐type form which is roughly 1.1 kcal/mol more stable than its N‐type counterpart. The hydroxyproline ring system in neutral or acidic medium displays a pure N‐type state, but N‐acetylation results in the appearance of a minor (S‐type) conformation. Cyclic proline dipeptides similarly exist in a biased conformational equilibrium. The major form (77–88%) corresponds to the N‐type conformer observed in the solid state; the minor S‐form has not been observed before. In contrast, cyclic hydroxyproline dipeptides display complete conformational purity. Ranges of endocyclic torsion angles deduced for the various classes of pyrrolidine derivatives in solution are presented. Each torsion appears confined to a surprisingly narrow range, comprising about 4°–8° in most cases. In all, the p

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200610

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe physical properties of single, 5–8‐μm diameter, water‐swollen elastin fibers have been investigated on a microtest apparatus attached to a polarizing microscope. Analysis of the mechanical and optical properties at extensions below 100% indicate that the elastic modulus (G) has a value of 4.1 × 105N m−2, the average molecular weight of chains between crosslinks is in the range of 6000–7100, and the stress optical coefficient (C′) is 1 × 10−9m2N−1at 24°C. Analysis of the temperature dependence of the stress optical coefficient indicates that the polarizability of the random link decreases with increasing temperature, with an apparent activation energy for this process of the order of 1.6 kcal/mol. Analysis of the non‐Gaussian mechanical and optical properties at extensions above about 100% suggest that the chains between crosslinks contain approximately 10 “effective” random links, with each link consisting of 7–8 amino acid residues. These parameters for the random chains in the elastin network have been used to predict the dimensions of other random proteins. The close correlation of these predictions with published values for the dimensions of a series of proteins in solution in 6Mguanidinium hydrochloride provides an independent test of the appr

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200611

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

年代:1981

数据来源: WILEY