摘要:

AbstractApple fruit pectin was visualized in the electron microscope by the Kleinschmidt technique with Pt/Pd rotary shadowing, and also on benzalkonium‐treated, especially thin carbon films using ruthenium red stain. Apple pectin molecules formed reticulate associations, which were partly dispersed after increasing the charge density of the molecules by enzymatic demethylation. Sycamore callus pectin molecules were visualized by the benzalkonium‐ruthenium red technique as short rows of intensely electrondense dots, 3 nm across. Using the same technique, short sections of the ϕX174 RF DNA double helix were visualized and the existence of the B conformation in solution directly confirmed. These observations confirm the nature of chromotropism as indicated by physical studies and provide new evidence on the staining reactions of ruthenium

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140102

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe hypothesis is made that cooperative (homotropic) effects in aspartate transcarbamylase (ATCase) and closely related hybrid molecules can be treated on the same basis, by expressing the effects in terms of cooperative interactions between catalytic sites. Then, provided the hybridCnnnCsss[R] exhibits cooperativity experimentally, it is deduced that at least two parameters are required for a consistent description of cooperative effects in ATCase.On this basis, a quantitative model is proposed that has cooperative interactions of two types: (1) a cooperative interaction of strengthUbetween a pair of native catalytic sites situated in different catalytic trimers, and joined by a regulatory dimer; (2) an indirect cooperative interactionŪ, between any pair of native catalytic sites in the same catalytic trimer, which is transmitted via two regulatory dimers. The model is consistent with the observation that the isolated catalytic trimer does not exhibit cooperativity, and that cooperative effects require the integrity of the regulatory dimers.In this model, the hybrid moleculeCnnnCsss[R] becomes simply a one‐dimensional Ising model for three sites with pair interactionsŪ, and the hybridCnssCnss[R] becomes an Ising model for two sites with interactionU/3. The model of native ATCase is essentially two Ising systems (the catalytic subunits), each with three sites having intrasubunit pair interactionsŪ, coupled together with three intersubunit pair interactionsU.The parametersŪandUcan be determined by comparing the exact solutions for the saturation curves of the two Ising models with the curves obtained from cooperativity measurements on the corresponding hybrid molecules. The theory can be readily tested, when accurate experimental data become available, by substituting the values ofŪandUdetermined from the hybrids into the model of native ATCase, or into models of other h

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140103

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

年代:1975

数据来源: WILEY

摘要:

AbstractCharacterization of polyU immobilized chromatography was performed in order to use this technique as an analytical device. A method of analysis of the elution profile related to thermodynamic parameters was also developed.Sites of attachment of polyU to agarose gel activated by cyanogen bromide were studied using uridine diphosphate and adenine. Independent equilibrium dialysis of ApA for different states of polyU, in solution and immobilized in gel, were carried out. These results show that the immobilized polyU is attached to agarose only at the 5′‐terminal phosphate groups and behaves as it does in solution.Column chromatography of ApA with the immobilized polyU was performed at several temperatures and concentrations. To analyze the elution profile, the theory of cooperative binding of oligonucleotides to polynucleotides was extended to the frame‐work of plate theory. A computer simulation for the elution profiles was performed using thermodynamic parameters obtained by equilibrium dialysis. This simulation duplicated the experimental results. This fact shows that the peculiar leading form of elution profile is due to the cooperative binding. The thermodynamic parameters of the polyU–ApA system were obtained from the “peak tr

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140104

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe synthesis of uridylyl‐3′‐5′‐nucleosides containing ribose, deoxyribose, or 2′‐fluoro‐2′‐deoxyribose in the uridine‐3′‐bound moiety and adenosine, guanosine, cytidine or uridine in the 5′‐nucleoside is reported. The temperature dependence of the circular dichroism of these dinucleoside phosphates in 0.06Mphosphate buffer at pH 7 was analyzed by the two‐state model and the oscillating dimer model. From the former, apparent thermodynamic parameters were determined by means of an iterative computer method. The comparison between the three different dinucleoside phosphates in each series indicated that the fluororiboside and the riboside resembled each other and were more stacked than the analogue containing deoxyribose. It further appeared that the similarity between the fluororiboside and the riboside is influenced by the nature of the neighboring 5′‐bound base. The interaction between the 3′‐bound sugar moiety and the 5′‐bound base is e

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140105

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

年代:1975

数据来源: WILEY

摘要:

AbstractPoly(Nε‐stearyl‐L‐lysine) and poly(Nε‐pelargonyl‐L‐lysine) were synthesized both by polymerization ofNε‐pelargonyl andNε‐stearyl‐L‐lysine NCA and by acylation of poly(L‐lysine) with pelargonyl and stearyl chloride. This second route has proven to be very useful, since completely acylated polymers are obtained in almost quantitative yield, whereas the usual scheme of preparation of ε protected poly(L‐lysine) cannot easily be applied due to solubility problems.Poly(Nεpelargonyl and stearyl‐L‐lysine) are soluble in alcohols containing linear aliphatic chains such asn‐butanol andn‐octanol and in mixtures of these alcohols with hydrocarbons such asn‐hexane andn‐heptane. Both polymers show an α‐helical conformation in the above solvents, which can be disrupted upon addition of sulfuric acid. Also in the solid state, poly(Nε‐stearyl‐L‐lysine) and poly(Nε‐pelargonyl‐L‐lysine)

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140106

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

年代:1975

数据来源: WILEY

摘要:

AbstractExperimental data are summarized on decay kinetics of uv‐induced paramagnetic centers in globular proteins. The PC decay rate in the absence of oxygen in α helical regions is shown to differ always by about two orders from that in nonhelical regions of the polypeptide chain. This effect can be utilized to estimate the degree of α helicity in the dry state, in solution, and in the frozen solution of prote

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140107

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

年代:1975

数据来源: WILEY

摘要:

AbstractWe report measurements of the diffusion coefficient of β‐lactoglobulin A (βLG‐A) at pH = 5.60 and 4.58 in 0.10 ionic strength acetate buffer by the techniques of analog photocurrent signal correlation and digital single‐clipped photon correlation. At a concentration of 21 mg/ml and a pH of 4.58, the self‐association of β‐lactoglobulin can be represented by a simple dimer–octamer equilibrium model. We determined the translational diffusion coefficient of the dimer and that of the octamer using the scattering results of Kumosinski and Timasheff in a dimer–octamer mixture. Our analysis shows that the dimer βLG‐A does not change its size if the pH is varied from 5.60 to 4.58 and both species remain constant in size for temperature changes from 3.5° to 25°C Hydrodynamically, the octamers behave like closed‐packed spheres with an effective radius of about 45 Å according to the

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140108

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

年代:1975

数据来源: WILEY

摘要:

AbstractQuasi‐elastic light scattering as measured by intensity fluctuation (self‐beat) spectroscopy in the time domain can be profitably used to follow both the translational diffusionDand the dominant internal flexing mode τintof DNA and its complexes with various histones in aqueous salt solutions. Without histones, DNA is found to haveD= 1.6 × 10−8cm2/sec and τint≅ 5 × 10−4sec in 0.8MNaCl, 2Murea at 20°C. Total histone as well as fraction F2A induce supercoiling (D= 2.6 × 10−8cm2/sec, τint≅ 2.8 × 10−4sec) whereas fraction F1 induces uncoiling (D= 1.0 × 10−8cm2/sec, τint≅ 9.4 × 10−4sec). Upon increasing the salt concentration to 1.5Mthe DNA–histone complex dissociates (D= 1.8 × 10−8cm2/sec). Upon decreasing the salt concentration to far below 0.8M, the DNA–histone complex eve

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140109

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

年代:1975

数据来源: WILEY

摘要:

AbstractA theroy relating rotational Brownian motion to the time autocorrelation function of the intensity of radiation from a fluorescent system composed of spherical rotors is presented. The calculation shows three relaxation times, two associated with the rotational diffusion, and the third associated with the natural decay of the fluorescence. The correlation function contains terms that relax independently of the fluorescence decay time, thus arbitrarily extending the time range over which rotational diffusion can be studied by fluorescence.

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140110

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

年代:1975

数据来源: WILEY

摘要:

AbstractMeasurements of electric birefringence, sedimentation velocity, and biological adsorption rate are used to study the properties of bacteriophage T4B in the presence of excess tryptophan. The adsorption rate determined in borate buffer pH 9 (at 25°C) increases from 0.003 × 10−8ml min−1(0.025M) to 0.130 × 10−8ml min−1(0.150M). The Kerr coefficient, rotational diffusion coefficient, and the sedimentation coefficient of the phage are also dependent on buffer concentration and reach plateau values above 0.12Mgiven byKsp= −(275 ± 18) × 10−9OD−1cm2statvolt−2,D25,w= 133 ± 4 sec−1, ands20,w= 818 ± 11S. From a comparison of electric birefringence measurements of T4B and T4D it is concluded that T4D and T4B (in the presence of excess tryptophan) exhibit a similar hydrodynamic behavior. The change in physical parameters is solely due to a shift in fiber configuration. At high buffer concentrations the fibers make an angle of approximately 3π/4 with the sheath and the permanent dipole moment is about 200,000 D. This dipole moment is roughly ten times as large as that of a phage particle with nonextended fibers. This difference may be due to a change in hydrodynamic center upon fiber extension or to the presence of positive charges on the fiber tips, or both. At intermediate buffer concentrations the phage population behaves as if it were monodisperse. Probably not all six fibers are exten

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140111

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

年代:1975

数据来源: WILEY