ISSN:0006-3525    

DOI:10.1002/bip.360230102

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe specific secondary structure of a number of polypeptide hormones of the pituitary gland anterior lobe and their fragments were studied by CD in the peptide bond absorption region and by ir spectroscopy. The state of objects was examined in solvents of different polarity over a wide temperature range as well as in the solid state at different relative humidities. The predominant conformational state of a number of hormones in aqueous solution is shown to represent a left‐handed helix of the poly(L‐proline) II type. The reversible melting process of the left‐handed helical conformation when heated in an aqueous solution appears to be noncooperative. Lowering the temperature stabilizes the left‐handed structure. The transition mode of the left‐handed form to the α‐, and the β‐forms on changing the solvent conditions was also studied. Contributions of peptide chromophores and of the aromatic amino acid side‐group chromophores with CD bands in the region under study were determined by analysis of CD spectra. The data obtained allow correlating the conformation of separate fragments in the hormone chain with fu

ISSN:0006-3525    

DOI:10.1002/bip.360230103

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

年代:1984

数据来源: WILEY

摘要:

AbstractA general method is presented for computing the atomic coordinates of helices in which a dipeptide is the repeating unit. The method will generate both single‐ and double‐stranded model helices having idealized bond lengths and angles, and any arbitrary, user‐specified, pitch and number of residues per turn. The variation of inter‐ and intrastrand hydrogen bonds with pitch and number of residues per turn can thus be examined. An application of the method is the construction of a β‐helix having pitch of 6.3 Å per turn and 4.85 residues per turn, a model which can pack nicely into the unit cell of crystals of cation‐bound

ISSN:0006-3525    

DOI:10.1002/bip.360230104

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

年代:1984

数据来源: WILEY

摘要:

AbstractWe treat the problem of the mean time of complete separation of complementary chains of a duplex containingNbase pairs. A combination of analytical and computer methods is used to obtain the exact solution in the form of a compact expression. This expression is used to analyze the limits of application of the equilibrium theory of helix–coil transition in oligo‐ and polynucleotides. It also allows the melting behavior of a biopolymer to be predicted when its melting is nonequilibrium. In the case of oligonucleotides for which the equilibrium melting takes place at a high value of the stability constants, the general expression turns into the equation of Craig, Crothers, and Doty, used by them to determine the rate constantkfof the growth of a helical region from temperature‐jump experiments. For the case of fragmented DNA withN∼ 102, the melting process is shown to be completely nonequilibrium, and as a result, the observed melting temperature should be higher than that for the equilibrium. A simple equation is obtained that makes possible calculation of the real, “kinetic” melting temperatureTk. AsNincreases, the observed melting temperature should approach the equilibrium value,Tm. This analysis has explained quantitatively the peculiar chain‐length dependence of the experimentally observed shift in the DNA melting temperature during fragmentation. A thorough analysis is given of the nonequilibrium effects in the melting process of long DNA molecules (N≳ 103). The main conclusion is that even in the presence of profound hysteresis phenomena, the melting profile observed on heating may differ only slightly from the equi

ISSN:0006-3525    

DOI:10.1002/bip.360230105

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe dielectric properties, DC electrical conductivity, andI‐Vcharacteristics of thin films of polyelectrolyte complexes formed by glycol chitosan (GlChi) with mucopolysaccharides chondroitin sulfate A (CSA), chondroitin sulfate C (CSC), and hyaluronic acid (HA) have been studied at different temperatures. The dielectric constant and the loss factor were measured at frequencies ranging from 1 to 100 kHz at all temperatures. The behavior of GlChi–CSA and GlChi–CSC complexes resembles that of the GlChi–dextran sulfate complex reported earlier. The GlChi–HA complex behaves differently and is similar to the GlChi–alginic acid complex reported [Srinivasan, R.&Kamalam, R. (1982)Biopolymers21, 251–

ISSN:0006-3525    

DOI:10.1002/bip.360230106

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe structure of yeast tRNAAspin aqueous solutions has been analyzed in the light of results obtained from Raman spectra recorded at from 5 to 82°C and compared to those of tRNAPhe. Firm evidence is given of a reversible conformation transition for tRNAAspat 20°C. This transition is observed for the first time in the tRNA series. The low‐temperature conformation appears to have a more regular ribose–phosphate backbone and a more effective G base‐stacking. This conformational change, which occurs essentially in the D loop, could be connected to the existence of two (A and B) crystal forms obtained depending on crystallization conditions. The melting temperatures, which are different for each base stacking in tRNAAsp, lie in a range of about 70°C, much higher than for tRNAPhe. This fact is interpreted by a higher ratio of G‐C base pairs

ISSN:0006-3525    

DOI:10.1002/bip.360230107

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe DNA–ligand interactions of a series of phenanthridinium compounds with various combinations of amino, azido, and hydrogen functions at R3and R8were examined to determine the contribution of these particular substituents to ligand binding. Spectrophometric titrations using calf‐thymus DNA emphasized the importance of amino substituents in conferring a strong interaction and also stabilizing the interaction against reversal by high ionic strength. Although azido groups were not as effective as amino groups, they were more effective than hydrogen functions in enhancing the interaction. Furthermore, an amino substitution at R8was consistently, though only slightly, more effective than an amino substituent at R3. The results from superhelical titrations using plasmid pBR322 DNA demonstrated that analogs with amino and/or azido functions at both R3and R8produced the greatest unwinding, and compounds with an amino or an azido function at R8proved more effective than those with the corresponding amino or azido substituent at

ISSN:0006-3525    

DOI:10.1002/bip.360230108

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe structure of a crystalline cellulose I–ethylenediamine complex has been determined by x‐ray diffraction methods as part of an investigation of cellulose–solvent interaction. The complex studied is that formed when native ramie fibers are swollen in ethylenediamine and then vacuum‐dried. The unit cell is monoclinic with dimensionsa= 12.87 Å,b= 9.52 Å,c= 10.35 Å, and γ = 118.8°, and it contains disaccharide segments of two chains, with one ethylenediamine per glucose residue. The refined model contains parallel cellulose chains that are linked by hydrogen‐bonded ethylenediamine molecules. The chains along theb‐axis are packed in register, leading to stacks of chains analogous to those in chitin. All the hydroxyl groups are satisfactorily hydrogen‐bonded and each ethylenediamine forms four donor and two acceptor hydrogen bonds. From this work it can be seen that the interaction of cellulose I with ethylenediamine involves scission of the intermolecular hydrogen bonds followed by disruption of the stacks of quarte

ISSN:0006-3525    

DOI:10.1002/bip.360230109

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

年代:1984

数据来源: WILEY

摘要:

AbstractHuman fibrinogen was treated with thrombin in the presence of fibrinoligase (Factor XIIIa) and calcium ion at pH 8.5, ionic strength 0.45, and the ensuing polymerization was interrupted at various time intervals (t) both before and after the clotting time (tc) by solubilization with a solution of sodium dodecyl sulfate and urea. Aliquots of the solubilized protein were subjected to gel electrophoresis on polyacrylamide gels after disulfide reduction by dithiothreitol and on agarose gels without reduction. The degree of γ‐γ ligation was determined from the former. The latter provided the size distribution of ligated end‐to‐end sequences produced by splitting the ligated staggered overlapped oligomers down the middle, for degrees of polymerization,x, from 1 to 10. Addition of fibrinoligase (in which the activating thrombin had been inhibited byp‐nitrophenyl‐p′‐guanidinobenzoate, NPGB) to Kabi fibrinogen showed the presence of small amounts of ligatable oligomers. Addition of fibrinoligase to a polymerizing mixture in which the action of thrombin had been stopped before clotting by NPGB produced the same distribution of ligated end‐to‐end sequences that was obtained when fibrinoligase was originally present, at least for reaction times up to 0.7 of the clotting time. The kinetics of γ‐γ ligation by fibrinoligase acting on a polymerized mixture stabilized by NPGB were followed. The reaction was first order in the concentration of ligatable γ‐γ junctions and the initial velocity was proportional to the enzyme concentration. The time evolution of size distribution of ligated end‐to‐end sequences agreed with a theory based on random

ISSN:0006-3525    

DOI:10.1002/bip.360230110

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

年代:1984

数据来源: WILEY

摘要:

AbstractIntercalation complexes of daunomicin(+1) with tetramer duplexes in DNA are studied with the theoretically determined intercalation sites (I, −0.4), (II, −0.4), and (III, −1.4). These sites occur with base pairs separated by 6.76 Å for helical angles of 26°, 22°, and 8° about the intercalation site. Site I is preferred, and this is in agreement with experimental unwinding angles. Optimum binding positions and conformations are established, and these are in agreement with experimental results from crystal structures. A systematic procedure is devised to study base‐pair and base‐sequence specificity, which results in the demonstration that the most stable sequences are mainly ↑BP1, T·A, DAUN, A·T, BP4↓ and ↑BP1, T·A, DAUN, G·C, BP4↓, i.e., with the TpA and CpG (pyrimidine)p(purine) sequences about the intercalation site. These 32 possible sequences are found among the 40 most stable complexes. These theoretical calculations of intercalation complexes with daunomicin(+1) provide the first example in which a drug specifically selects the base pair T·A and prefers it in a particular sequence about the intercalation site. This specificity is in agreement with some experimental results. Problems associated with the interpretation of specificity are discussed in terms of the base, base‐pair, and base‐sequence resulting from the DNA site and the DNA–drug interactions. T·A specificity is rationalized by noting that the 2′deoxyribo‐5′‐monophosphate backbone attached to A is slightly more negative than that on the other nucleotides. Hence, a preference exists for binding to the protonated daunosamine (+1) groups. Stereographic projections of daunomycinone and daunomycin(+1) in a bond model and in a space‐filling model

ISSN:0006-3525    

DOI:10.1002/bip.360230111

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

年代:1984

数据来源: WILEY