摘要:

Abstractβ‐Helical poly(L‐glutamic acid) in a gel state was found to be easily converted to the antiparallel β form by heating. Two β forms were obtained, depending on the temperature of heating. Temperatures between 40° and 85°C produced a β form with a spacing between pleated sheets (d001) of 9.03 Å, termed β1. If the heating was carried out at temperatures higher than 85°C, the β1form underwent another conformational transition reducing the d001value from 9.03 to 7.83 Å (termed β2) without any prominent change in the fiber repeat distance (i.e., the polypeptide backbone conformation). The time course of these two transitions was followed by measuring the infrared spectra of the samples, and it was concluded that the α → β1transition in its initial stage obeys a pseudo‐first order rate process with activation enthalpy and entropy of 54 kcal/mol and 92 eu, respectively. On the other hand, the typical sigmoidal conversion curves observed for the transition between the two types of β forms (β1→ β2) indicate that this transition proceeds via a socalled “nucleation and growth” process. The kinetic theory of phase transitions developed by Avrami can be applied with success to explain this transition. The infrared spectra, in the region from 1800 to 200 cm−1, were measured for these two β forms and the results showed that the conformation of the side chains and the mode of the hydrogen bonding between the side‐chain carboxyl groups undergo appreciable change during the transition.The heat‐induced conformational transition of poly(L‐Glu78L‐Val22) was also studied. The copolymer was transformed from the α‐helical conformation directly to the β2form. The reason for this was thought to be due to the fact that theL‐valine residues and theL‐glutamyl residues near theL‐valine residues hav

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150302

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe molecular theory of the previous paper in this series is extended to determine the effect of divalent metal ions on helix stability relative to coil at fixed ionic strength and nucleotide phosphate concentration. Specification of the state of condensed counterions, as well as their concentration, is essential for the solution of this problem, and it is assumed that they translate freely within a thin cylindrical shell close to the polynucleotide. As a function of divalent counterion concentrationm B 2+the relative stability of the helix is highly nonlinear. Although the overall trend is that the helix stability increases with addition of divalent metal ion, there is a narrow concentration range for which it decreases slightly. The behavior of the relative stability as a function ofm B 2+is determined by the translational degrees of freedom of the counterions, both univalent and divalent, both condensed and uncondensed. Detailed comparison of the theory with data is not given here, but it is pointed out that the calculated values of the relative stability are consistent with the order of magnitude of the observed effect Mg2+on the melting temp

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150303

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

年代:1976

数据来源: WILEY

摘要:

AbstractConnective tissue proteoglycans undergo interaction with poly(L‐arginine) when mixed in dilute neutral aqueous solution. Circular dichroism spectroscopy indicates that the polypeptide adopts the α‐helical conformation rather than the extended coil form normally observed at neutral pH. The interactions of a series of proteoglycans with different protein and glycosaminoglycan contents have been compared. The arginine/disaccharide residue ratio at maximum interaction appears to be constant with varying protein content of the proteoglycans that contain chondroitin 4‐sulfate. The thermal stability of the proteoglycan interaction is the same as for the component polysaccharide. Thus in terms of the strength of interaction with homopolypeptides, the properties of proteoglycan and the component glycosaminoglycans are the same, and this is likely also to be the case for collagen–proteoglycan systems.The interactions of keratan sulfate‐2 have also been investigated. These are similar but have much lower thermal stability than corneal keratan sulfate‐1. The results are consistent with the weak interaction of the keratan sulfate‐2 component of bovine nasal septu

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150304

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe existence and distribution of vertical, interacting edges on cylindrical surfaces, which were derived from the basic structural features of the collagen molecule, have been examined as a function of the angle θ of the superhelix. Over the range θ = 26°–33° and near θ = 36°, the strongest intermolecular association was detected at 29.95°. This model exhibited three similar, self‐interacting edges, separated by approximately 120°. The potential for three similar but nonidentical edges lies in the geometry of the collagen molecule, but the existence of such edges and their ability to self‐associate is dependent upon the unique amino acid sequence. The relative strengths of association of each edge with itself and with the other edges are not identical, but the present analysis does not permit a judgment as to whether this variation could result in functional specificity in such interactions. All three chains participate in each edge though their contribution to the relative interaction strength is not identical.These edges showed distinct maxima when displaced past one another by integral intervals ofD, whereD= 233 residue positions (quarter‐stagger). The strongest relative interaction occurs at a dis

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150305

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

年代:1976

数据来源: WILEY

摘要:

AbstractX‐ray diffraction studies have been made on the polytripeptide poly(L‐prolyl‐L‐α‐phenylglycyl‐L‐proline). Its structure has been found to be helical, with a poly(L‐proline) II conformation, packed in an orthorhombic lattice, space group P21212, witha= 14.3 Å,b= 13

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150306

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

年代:1976

数据来源: WILEY

摘要:

AbstractIt is argued that the decrease of fluorescence depolarization observed when diphenylanthracene is dissolved in poly(γ‐benzyl‐L‐glutamate) or polystyrene solution is due to short‐range interactions, and not to long‐range hydrodynamic interactions. Estimates of the hydrodynamic effect are given. Rough estimates of the effect to be expected on the short‐range hypothesis are in qualitative agreement wit

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150307

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

年代:1976

数据来源: WILEY

摘要:

AbstractCircular dichroism spectra for acid‐soluble calfskin collagen, gelatin, and poly(proline) II in solution have been extended into the vacuum ultraviolet region. The extended spectrum of gelatin reveals that the circular dichroism of this unordered polymer is more closely related to the spectrum of charged polypeptides than might be evident from near ultraviolet work. A short‐wavelength band is found at about 172 nm, which corresponds in position, magnitude, and sign to a band recorded earlier for poly(L‐glutamic acid) at pH 8.0. This band is observed in a helical structure for the first time in the vacuum ultraviolet circular dichroism and absorption spectra of poly(proline) II. Both circular dichroism and absorption spectra point to the assignement of this band as thenσ*. Neither thenσ* nor the expected positive lobe of the ππ* helix band is observed in the extended circular dichroism spectrum of collagen. We postulate that these two bands cancel here in analogy to the case of α‐helical poly(L‐

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150308

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe thermal stability of a new polynucleotide complex has been used to establish the hydrogen‐bonding structure of three‐stranded C‐G·CH+helices. In the Hoogsteen structure, the 8NH2group of 8NH2GMP can form a third hydrogen bond to the CH+strand, but in the alternative structure, the 8NH2group can form no interbase hydrogen bonds. For the new complex, 8NH2GMP·2 poly(C), a transition temperature of 80°C is observed under conditions in which the corresponding complex formed with 5′‐GMP has aTmof 20°C. We conclude from this 60° elevation of transition temperature that a third hydrogen bond is formed by the 8NH2group and that the structure must have Hoogsteen bonding. In order to be compatible with this structure in regular helices formed by U,C copolymers, A·2U bonding would also have to have a Hoog

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150309

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe Watson–Crick imino and amino exchangeable protons, the nonexchangeable base and sugar protons, and the backbone phosphates for d‐CpG(pCpG)n,n= 1 and 2, have been monitored by high‐resolution nmr spectroscopy in aqueous solution over the temperature range 0°–90°C. The temperature dependence of the chemical shifts of the tetramer and hexamer resonances is consistent with the formation of stable duplexes at low temperature in solution. Comparison of the spectral characteristics of the tetranucleotide with those of the hexanucleotide with temperature permits the differentiation and assignment of the cytosine proton resonances on base pairs located at the end of the helix from those in an interior position. There is fraying at the terminal base pairs in the tetranucleotide and hexanucleotide duplexes. The Watson–Crick ring imino protons exchange at a faster rate than the Watson–Crick side‐chain amino protons, with exchange occurring by transient opening of the double helix. The structure of the d‐CpG(pCpG)ndouble helices has been probed by proton relaxation time measurements, sugar proton coupling constants, and the proton chemical shift changes associated with the helix–coil transition. The experimental data support a structural model in solution, which incorporates ananticonformation about the glycosyl bonds, C(3)exosugar ring pucker, and base overlap geometries similar to the B‐DNA helix. Rotational correlation times of 1.7 and 0.9 × 10−9sec have been computed for the hexanucleotide and tetranucleotide duplexes in 0.1Msalt, D2O, pH 6.25 at 27°C. The well‐resolved31P resonances for the internucleotide phosphates of the tetramer and hexamer sequences at superconducting fields shift upfield by 0.2–0.5 ppm on helix formation. These shifts reflect a conformational change about the ω,ω′ phosphodiester bonds fromgauche‐gauchein the duplex structure to a distribution ofgauche‐transstates in the coil structure. Significant differences are observed in the transition width and midpoint of the chemical shift versus temperature profiles plotted in differentiated form for the various base and sugar proton and internucleotide phosphorous resonances monitoring the d‐CpG(pCpG)nhelix–coil transition. The twofold symmetry of the d‐CpGpCpG duplex is removed on complex formation with the antibiotic actinomycin‐D. Two phosphorous resonances are shifted downfield by ∼2.6 ppm and ∼1.6 ppm on formation of the 1:2 Act‐D:d‐CpGpCpG complex in solution. Model studies on binding of the antibiotic to dinucleotides of varying sequence indicate that intercalation of the actinomycin‐D occurs at the GpC site in the d‐CpGpCpG duplex and that the magnitude of the downfield shifts reflects strain at the O‐P‐O backbone angles and hydrogen bonding between the phenoxazone and the phosphate oxygens. Actinomycin‐D is known to bind to nucleic acids that exhibit a B‐DNA conformation; this suggests that

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150310

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

年代:1976

数据来源: WILEY

摘要:

AbstractCircular dichroism spectra have been obtained for tri(L‐lysine), tetra(L‐lysine), and penta(L‐lysine) in aqueous sodium dodecyl sulfate at 25°C. None of the oligomers are affected significantly by sodium dodecyl sulfate at detergent concentrations exceeding 0.01M. Literature results show that the high‐molecular‐weight polymer forms a β strucure under these conditions. At detergent concentrations near 3.5 × 10−4Mthe penta(L‐lysine), but not the smaller oligomers, undergoes a conformational change. Its circular dichroism under these conditions is essentially identical to that observed with poly(L‐lysine) when it forms a β structure in sodium dodecyl sulfate. Solutions of the penta(L‐lysine), which exhibit this modified circular dichroism, are also turbid, leading to the conclusion that the oligomer has formed an intermolecular β structure. When these experiments are conducted in the presence of 0.1Msodium hydroxide, the sodium dodecyl sulfate produces neither turbidity nor a modified circular dichroism spectrum. These observations provide compelling evidence that Coulombic interaction between the anionic detergent head and the cationic lysyl amino groups is essential for the conformational change induced in penta(L‐lysine) b

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150311

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

年代:1976

数据来源: WILEY