摘要:

AbstractCrustacean and yeast cell wall chitin were analyzed by means of transmission electron microscopy and selected‐area diffraction. Single fibrils 8–25 nm wide have been observed in the micrographs of crustacean chitin. Analysis of a series of diffraction patterns obtained from thin crustacean chitin platelets yielded results which were in a better agreement with the theoretical structural model than those measured earlier. In this respect electron diffraction is shown to be superior to the more commonly used x‐ray diffraction. Yeast cell wall chitin had a less perfect structure than the crustacean chitin. Single fibrils were not observed on the micrographs and electron diffraction patterns did not show any preferred fiber orientation. The evaluation of electron‐diffraction patterns of both the primary septum and the adjacent circular zone of scar ring led to the conclusion that α‐chitin is present in both these parts of the mothe

ISSN:0006-3525    

DOI:10.1002/bip.360210102

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

年代:1982

数据来源: WILEY

摘要:

AbstractComputer simulation shows that the time required to attain near sedimentation equilbrium is dramatically reduced by a two‐step initial loading in which a macromolecular solution at low or zero concentration is layered above one at a higher concentration. To achieve the minimum time requires a good estimate of the molecular weight, but at least a 50% reduction in time can be achieved if the molecular weight of the macromolecule is known only within a factor of 2. Numerical solutions to the differential equation of the ultracentrifuge are calculated using the finite element method. An efficient Gaussian elimination algorithm can be used to minimize calculation time and computer storage requirement

ISSN:0006-3525    

DOI:10.1002/bip.360210103

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

年代:1982

数据来源: WILEY

摘要:

Abstract(L‐Cys)n+N‐base systems and (L‐Cys)n+ (L‐Lys)nsystems were studied by ir spectroscopy. It is shown that in the water‐free systems, SH ⃛N ⇌ S−⃛H+N hydrogen bonds are formed. With the (L‐Cys)n+N‐base systems, both proton‐limiting structures in the SH ⃛N ⇌ S−⃛H+N bonds have equal weight when the pKaof the protonatedN‐base is 2 pKaunits larger than that of (L‐Cys)n. The same is true with the water‐free (L‐Cys)n+ (L‐Lys)nsystem. Thus, with regard to the type of proton potentials present, these hydrogen bonds are proton‐transfer hydrogen bonds showing very large proton polarizabilities. This is confirmed by the occurrence of continua in the ir spectra. Small amounts of water open these hydrogen bonds and increase the transfer of the proton to (L‐Lys)n. In the (L‐Lys)n+N‐base systems, with increasing proton transfer the backbone of (L‐Cys)nchanges from antiparallel β‐structure to coil. In (L‐Cys)n+ (L‐Lys)n, the conformation is determined by the (L‐Lys)nconformation and changes depending on the chain length of (L‐Lys)n. Finally, the reactivity increase in the active center of fatty acid synthetase, which should be caused by the shift of a proton, is discussed on the basis of the gre

ISSN:0006-3525    

DOI:10.1002/bip.360210104

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

年代:1982

数据来源: WILEY

摘要:

AbstractHigh‐resolution neutron time‐of‐flight (TOF) spectra were measured for partly deuterated hen egg‐white lysozyme in solution with and withoutN‐acetyl‐glucosamine inhibitor bound to the cleft, and in polycrystalline form. Weak but reproducible bands occur at frequencies between 25 and 375 cm−1. The bands were tentatively assigned on the basis of previous results for homopolypeptides. At very small energy transfers (between about 1 cm−1and 40 cm−1), the TOF spectra show a dependence both on inhibitor binding and crystalline environment. This is interpreted in terms of conformat

ISSN:0006-3525    

DOI:10.1002/bip.360210105

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

年代:1982

数据来源: WILEY

摘要:

AbstractWater‐soluble, random copolymers containingL‐glutamine and eitherN5‐(3‐hydroxypropyl)‐L‐glutamine orN5‐(4‐hydroxybutyl)‐L‐glutamine were synthesized, fractionated, and characterized. The thermally induced helix–coil transitions of these copolymers were studied in water. A short‐range interaction theory was used to deduce the Zimm‐Bragg parameters σ andsfor the helix–coil transition in poly(L‐glutamine) in water from an analysis of the melting curves of the copolymers in the manner described in earlier papers. The computed values ofsindicate thatL‐glutamine is helix‐indifferent at low temperature and a helix‐destabilizing residue at high temperature in water. At all temperatures in the range of 0–70°C, the glutamine residue promotes helix–coil boundari

ISSN:0006-3525    

DOI:10.1002/bip.360210106

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe aldehydes present in acid‐soluble type I collagen react with pyrenebutyrylhydrazine to form various types of complexes under different reaction conditions. These complexes exhibit one or more of three different pyrene fluorescence bands: monomer, excimer, and aggregate fluorescence. Collagen, whose aldehydes have been reduced with NaBH4, does not react with this fluorescent hydrazine, confirming that the hydrazine reacts specifically with aldehyde groups to form hydrazones. The absence of a reaction with pepsin‐treated collagen also shows that the fluorescent labels are primarily in the nonhelical terminal telopeptides. Upon dialysis, the pyrene label bound to a saturated aldehyde in an α‐chain is lost; whereas that bound to an unsaturated aldehyde remains on the protein. The pyrene monomer fluorescence in the β‐chain of old collagen is stronger than that of young collagen. The formation of the pyrene excimer fluorescence implies the proximity of two pyrene molecules, probably attached to two adjacent aldehydes. Upon changing from acidic to neutral pH, both excimer and aggregate fluorescence bands disappear within a few seconds, revealing a very rapid alteration at the tel

ISSN:0006-3525    

DOI:10.1002/bip.360210107

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

年代:1982

数据来源: WILEY

摘要:

AbstractTransient electric dichroism has been measured for the ferriheme–poly(L‐lysine)[(Lys)n], ferroheme–(Lys)n, and ferroheme–(Lys)n–carbon monoxide (CO) solutions at pH 9–12. The Soret absorption maximum in electronic spectrum (λ), the reduced linear dichroism (ρ∞) at complete orientation and the calculated angle (ϕ) between the porphyrin plane of a bound heme and the oriented polymer axis are determined for the following complexes: a ferriheme–(Lys)ncomplex at pH 9.5–10.5 (λ = 420 nm, ρ∞= 0.50, and ϕ = 19°), a ferroheme–(Lys)ncomplex at pH 9.5–10.2 (λ = 432 nm, ρ∞= 0.77, and ϕ = 0°), and a ferroheme–(Lys)n–CO complex at pH 9.25 (λ = 430 nm, ρ∞= 0.38, and ϕ = 24°). Based on the above data, the validity of the structures of heme–(Lys)ncomple

ISSN:0006-3525    

DOI:10.1002/bip.360210108

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

年代:1982

数据来源: WILEY

摘要:

AbstractWe report electric‐dichroism and electron‐microscopic studies of chromatin fibers fixed by protein–protein crosslinking at salt concentrations ranging from 10 to 100 mM. The results confirm a progressive disorganization of the fiber as the salt concentration is lowered. The positive dichroism and large polarizability anisotropy characteristic of the 300‐Å diameter fiber found in 100 mMsalt are replaced by negative dichroism and smaller effective polarizability anisotropy or dipole moment for samples fixed at lower salt concentration. We interpret the results in terms of segmental, field‐induced orientation of the disorganized structure which is present in low salt concentrations. We also observed a field‐induced absorbance decrease in chromatin fibers fixed at salt concentration at and below 100 mM. All three optical effects, namely overall orientation of the high‐salt fixed fiber, segmental orientation of the low‐salt fixed fiber, and field‐induced absorbance decrease, occur on roughly the same time scale, 20–100 μs for 50 nucleosome polynucleosomes. The polarizability anisotropy of fibers fixed in 100 mMsalt was found to be proportional to the length of the fragment and to the reciprocal square root of the conductivity of the solution used for electric‐dichroism measurements. Addition of Mg2+to the measurement buffer affected the dichroism amplitude of samples fixed below 100 mMsalt but not those fixed at 100 mMsalt. The results reinforce the need for caution in interpreting electric‐dichroism measurements on chromatin fibers because of possible field

ISSN:0006-3525    

DOI:10.1002/bip.360210109

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

年代:1982

数据来源: WILEY

摘要:

AbstractA melting experiment was performed on the whole set of populations of the replicative form of ϕX174 DNA, which can be obtained treating this DNA with rat liver nicking‐closing enzyme in the presence of ethidium bromide. Gel electrophoresis performed by loading the DNA samples at neutral and alkaline pH allows separation of these populations in discrete sets of bands, which can then be compared. The outcome of the experiments indicates that in the range of electrophoretic mobilities which can be explored, no band is formed exclusively by circular complementary strands which can be separated by alkaline denaturation. These results are compared with what would be expected if double‐stranded closed circular DNA had structures other than the canonical double helix. Under nonrestrictive hypotheses, the experiments reported allow one to obtain a minimum estimate of the absolute value of the linking number of a closed circular double‐stranded DNA: for native ϕX174 RF DNA, the linking number appears to be greater than 12 (in absolute value). Some data on the electrophoretic mobility of denatured closed circular duplexes are reported, which still wait for a physicochemical interpr

ISSN:0006-3525    

DOI:10.1002/bip.360210110

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe stability of the α‐helices of isomeric block copolypeptides is nonequivalent, as reported previously. In order to explore the origin of the nonequivalence, the stability of α‐helix of two block copolypeptides, (L‐Ala)20‐(L‐Glu)20‐(L‐Phe) (designated as AEF) and (L‐Glu)20‐(L‐Ala)20‐(L‐Phe) (EAF), in aqueous solution was investigated as a function of pH, temperature, and salt concentration by the measurement of the α‐helical content using CD at 223 nm. The transition temperature,Tm, as a measure of the stability of the α‐helix, decreased with increasing the salt concentration for EAF, whileTmincreased for AEF. The results indicate that electrostatic interactions affect the nonequivalence of such helical stability. Thermodynamic quantities, ΔG, ΔH, and ΔS, of the thermal transition from random coil to α‐helix were obtained by applying the curve‐fitting method to the data. The major contribution to the effects of salts seems to be the entropic term, not the enthalpy term. This is unexpected, since the salt ions would weaken electrostatic interactions between ionized groups and the dipole along the helical axis, which affect the enthalpy term. In addition, the dependence of the electrostatic effect on the salt concentration is different for EAF and AEF. There fore, the nonequivalence cannot be accounted for by only the electrostatic effect, suggesting that it originates from

ISSN:0006-3525    

DOI:10.1002/bip.360210111

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

年代:1982

数据来源: WILEY