摘要:

AbstractSerum albumin undergoes a conformational change at pH 4, known as the N–F transition. In the customary Linderstrøm‐Lang treatment of hydrogen ion titration, the carboxyl groups in serum albumin either have an abnormally low pK, or are buried in charged form, and the Linderstrøm‐Lang charging parameter ω decreases dramatically at the N–F isomerization. In the present paper partition functions are derived and distribution functions are calculated for a model permittingsalt bondingbetween the positively and negatively charged sites on a macromolecule. The N‐form has an abnormally high salt bonding constant whereas that of the F‐form corresponds to that of small ions. The result obtained is consistent with a “normal” intrinsic pK of the carboxyl groups of serum albumin without burying of any charges and with an unchanged ω. The nature of the postulated salt bonding is discussed.Further, it is shown that the “abnormal salt bonding” of serum albumin can explain its unusual ability to bind anions. Theoretical binding curves are calculated and compared with literature data of the Cl−binding of serum albumin. The relation of the present model to other models of hydrogen ion and anion binding to proteins is discussed. Some additional consequences of the present model are pointed out; a transition in the alkaline range, analogous to the acid transition, seems probable. Literature data support the existence of such a transition but do not allow detailed calculations at present.A general, thermodynamic treatment of the interactions between small ligands and macromolecules is outlined. Important points are the choice of the statistical‐me‐ chanical ensemble and considerations of the fluctuations about the mean bonding, if (i) there are not only a ligand‐locus interaction but also interligand interactions (in par‐ ticular intdigand attraction), or (ii) there is a conformational change in themacromole‐ cule depending on the ligand binding. In these cases, the binding isotherms obtained from thermodynamicallyclosedsystems (canonical ensemble) may erroneously indicate a distribution about a single probability maximum, i.e., the statistical mean binding N̄, and fluctuations about this value. The description of a phase change in a bound phase or a change in the “internal” self‐interactions of a macromolecule requires a bind‐ ing equation permitting distributions about two maxima, i.e., (i)N1*N̄ (“condensed” phase) or (ii) two macromolecular conformations P′, and P″, having occupancy numbers N̄, and N̄2, respectively. The N–F transition is an example illustrating the relation between the c

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111102

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe high‐humidity X‐ray pattern of oriented fibers prepared from salmon spermheads strongly resembles that of DNA in the B form. However, the nucleoprotamine pattern has a more intense first layer line and increased lateral unit‐cell dimensions.Complexes of DNA with poly‐L‐lysine and poly‐L‐arginine were prepared and photographed at various relative humidities. The most crystalline patterns were obtained at 92% and also indicate DNA in the B form. However, whereas polylysine–DNA, like the spermheads, has a primitive hexagonal cell, polyarginine–DNA, like NaDNA, has three molecules in the unit cell. Polylysine–DNA, but not polyarginine–DNA, also resembles spermheads in having a strong first layer line.All three complexes show increasing intermolecular distance with increasing humidity, but with sharp maxima when photographed in water, which indicates cross‐linking between the molecules. Lowering the humidity causes the polylysine–DNA, but not polyarginine–DNA, to change conformation from the B to the C form.The structural implications of these results are discussed in the light of model‐building studies and a comparison of calculated a

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111103

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe pH, temperature, and reagent concentration dependences of the cyanuration of tyrosines within proteins are compared with those of the free amino acid. The results indicate that the mechanism of the cyanuration reaction is a nucleophilic aromatic substitution of the SN2 type, where the tyrosine oxygen acts as a nucleophile and the displacement takes places at a carbon atom which is part of the six‐membered ring of thes‐triazene. This reaction must compete with the hydrolysis of cyanuric fluoride in aqueous media. These competing reactions generate curves for the pH dependence of the reactivity of tyrosine with cyanuric fluoride whihc vary in a predictable manner with the extent of ionization of tyrosine and the concentration of cyanuric fluoride. In the case of proteins, the dependence of the degree of tyrosine reactivity on pH and temperature within the pH range of full reactivity of the free amino acid reflects constraints imposed by the microenvironment of these groups within the three‐dimensional structure of the macromol

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111104

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

年代:1972

数据来源: WILEY

摘要:

AbstractAlthough native B‐type starch loses its sharp X‐ray pattern on strong drying, the wet Nägeli amylodextrin prepared from such starch gives a sharp B‐pattern, that is only slightly reduced in sharpness by complete drying. Nägeli amylodextrin dried admixed with a noncrystalline “filler” (e.g., starch sirup) gives an X‐ray pattern essentially identical to that of the wet amylodextrin, except that the 16‐Å (No. 1) ring is greatly reduced in sharpness and intensity. Failure of the B‐structure to collapse during drying indicates that water is not intercalated between turns of a helix or otherwise required to maintain the geometry and packing arrangement of the starch molecular chains. Rather, for native starch granules or amylose fibers, water relieves intercrystallite strains and consequent crystallite distortion induced by strong drying. For Nägeli amylodextrin, the small molecules of starch sirup can penetrate the interstices between crystallites and prevent strain build‐up during drying. For native starch granules, the interstitial regions are gel‐like in character and less permeable to starch sirup molecules. A model for B‐starch is proposed, that employs int

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111105

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

年代:1972

数据来源: WILEY

摘要:

AbstractWe present a detailed theoretical study of nucleic acid distance distribution functions for chain lengths up to thirty‐five nucleotides. The distribution functions were found by the Monte Carlo techniques described previously and, where they are symmetric, by reconstruction from their even moments. A comparison of the two approaches allows an assessment of the utility of expansion procedures for stiff chains (C∞≈ 17), as a function of length and extension. It was found that for chains with fewer than fourteen nucleotides over seventy even moments were required to obtain a reliable function for extensionsR≥ (〈R2〉)1/2. On the other hand at thirty‐five nucleotides the first ten even moments were sufficient to reconstruct the distribution for all but extreme extensions.The other feature of the calculation is the prediction of a loop weighting function. It was found that for a thirty‐five nucleotide chain, the form of the distribution function is very nearly gaussian forR<(〈R2〉)1/2. Consequently a loop weighting function based on detailed crystallographic data is now known for all values ofN. The first derivative of the function is within 8% of the Jacobson‐Stockmayer value at 170 nucleotides, but differs severely from the latter for chains with less th

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111106

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe quasielastic light scattering of poly‐L‐lysine HBr in aqueous solutions has been examined over a variety of pH values where the polymer is in different conformations. Analysis of the spectra demonstrates that as the pH is lowered, the polymer changes from an extended anisotropic from through a collapsed randomized state to a larger isotropic form. These data support the current view that the polymer undergoes a conformational change from an α‐helical form to a “kinked” extended‐coil conformation through an intermediate partially α‐helical state in which internal packing of the helical portions occurs. Finally, a value for the rate of propagation of the unwinding of the α‐helix

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111107

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe degree of binding of acridine orange to DNA, native or denatured, has been determined by equilibrium dialysis in 0.1M and 0.001M NaCl at 20°. The nature of the binding process has been investigated by studying various optical properties of the dye–DNA complexes and by relating them to the binding ratio. All these properties were found to vary quantitatively and qualitatively according to the successive stages of the process. These stages were assumed to be a strong binding of intercalated monomers followed by formation of bound dimers and finally by external binding of aggregates of native DNA.Absorption spectra of the complexes could be interpreted on that basis.Circular dichroism spectra were resolved into components: one band for intercalated monomers without interactions, two excition splittings for interacting monomers and bound dimers, respectively, weak bands and exciton splitting for external aggregates.The fluorescence intensity was greatly enhanced in intercallated monomers; its quenching at higher binding ratio was quantitatively related to dimer fixation. The value of the anisotropy of fluorescence at low binding ratio suggested a limited mobility of intercalated monomers; the decrease of polarization at higher binding was attributed to energy transfer between monomers.Electric dichroism displayed by the complexes in the dye absorption bands indicated an orientation of the bound molecules quite parallel to the base rings at low binding. In the range of fixation of dimers and external molecules, the dichroism was lower but still indicated an important degree of orderi

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111108

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe circular dichroism (CD) spectra of poly‐L‐proline and of poly‐L‐glutamic acid and poly‐L‐lysine in their charged states have been studied as a function of temperature. The variation of CD spectra with temperature is inconsistent with the assignment of the spectrum of such charged polypetides to an unordered chain conformation, but does support our earlier assignment to a locally ordered structure—what we have called the extended helix conformation. These results also strengthen our previous assignment of the CD spectrum of an unordered chain, and indicate that three conformational states (α‐helix, extended helix, and unordered) should be incorporated in our thinking about conformational transitions

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111109

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

年代:1972

数据来源: WILEY

摘要:

AbstractConditions were studied under which aggregated complexes of histone F1 with DNA display a circular dichroic spectrum of nonconservative type characterized by two intense negative maxima at 269 nm and 209 nm. It was found that the intensity of the longwave band depends directly on the content of guanine plus cytosine and inversely on the molecular weight of DNA. The same type of dependence was found for DNA's of eukaryotic and bacterial origin. It appears that the formation of the nonconservative spectrum which can be ascribed to a certain structural form of DNA is caused by orientation of the DNA molecules in the aggregated complex and by specific interactions of the bases of the guanine–cytosine pair. The possible mechanism of formation of nonconservative dichroic spectrum is discussed with respect to special properties of guanin

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111110

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe effect of deuterium on the thermal stability of the polynecleotide double helix formed by the homopolymers polyadenylie acid (poly A)and polyuridylic acid (poly U)has been invertigated by measuring the best capacity as a function of temperature in an automatic scanning adiabatic calorimeter. Hydrogen‐bounded and deuterium‐bonded helical conformations of the polynecleotides used have been melted in H2O and D2O2respectively, as solvent. Within the limits of experimental error, there is no dfference in the measured enthallpy change accompanying the helix‐random coil transition. The enthalpy change ΔH is 6.6 Kcal/MBP ub any case. The half‐conversion temperatures Tmdiffer by two degrees. Tmfor poly (AU) in H2O is 45.8°C, Tmfor poly (AU) in D2i

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111111

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

年代:1972

数据来源: WILEY