摘要:

AbstractThe kinetics of biopolymerization on nucleic acid templates is discussed. The model introduced allows for the simultaneous synthesis of several chains, of a given type, on a common template, e.g., the polyribosome situation. Each growth center [growing chain end plus enzyme(s)] moves one template site at a time, but blocksLadjacent sites. Solutions are found for the probabilitynj(t)that a template has a growing center that occupies the sitesj—L+ 1,…,jat timet. Two special sets of solutions are considered, the uniform‐density solutions, for whichnj(t)=n, and the more general steady‐state solutions, for whichdnj(t)/dt= 0. In the uniform‐density case, there is an upper bound to the range of rates of polymerization that can occur. Corresponding to this maximum rate, there is one uniform solution. For a polymerization rate less than this maximum, there are two uniform solutions that give the same rate. In the steady‐state case, onlyL= 1 is discussed. For a steady‐state polymerization rate less than the maximum uniform‐density rate, the steady‐state solutions consist of either one or two regions of nearly uniform density, with the density value(s) assumed in the uniform region(s) being either or both of the uniform‐density solutions corresponding to that polymerization rate. For a steady‐state polymerization rate equal to or slightly larger than the maximum uniform‐density rate, the steady‐state solutions are nearly uniform to the single uniform‐density solution for the maximum rate. The boundary conditions (rate of initiation and rate, of release of completed chains from the template) govern the choice among the possible solutions, i.e., determine the region(s) of uniformity and the value(s) assum

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060102

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

年代:1968

数据来源: WILEY

摘要:

AbstractIn aqueous solutions of the amylase–iodine complex the concentration of free iodine [If]vafter reaching equilibrium (or closely approximating it) is determined by the following factors: temperature, pH, concentration of iodide ions and amylose, andDPof amylose. In the present paper the role of temperature, amylose concentration, andDPhas been investigated. At half‐saturation of amylose by iodine, the reciprocal value of free iodine defines the equilibrium constant: 1/[If]v=K. The relation between [If]v, in normality and temperature is the following: 5 + log [If]v= −(2.132/T) + 8.52, forDPn= 1290, 0.4 mg. amylose in 100 ml. 0.1NHCl. The value of the energy of activationEabetween 2 and 52°C. is 9.72 kcal./mole. The influence of amylose concentration [Am] on photometrically determined [If]v, at 20°C, in the range of 0.1–1.2 mg./100 ml. 0.1NHCl forDPn= 1290 is: 5 + log [If]v= 0.209 − 0.047 log [Am]. At [Am]= 0.6 mg. amylose/ 100 ml. 0.1NHCl and 20°C, the value of [If]vdepends onDPnas follows: 5 + log [If]v= 0.085 = + 0.222 log (104/DPn). These above equations are summarized by the relation: [If]v= exp {16.865 − (Ea/RT)}[Am]0.047(104/DPn)0.222×10−5Considering that the determination of [If]vby automatic photometric titration can be performed quickly and with appropriate reproducibility, this method is convenient for a rapid empirical and approximate determination ofDPof amylose on a microscale. The iodine‐binding capacity [IBC] as well as the value of λmax, have been also investigated as functions ofDPn, by photometric and by am

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060103

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

年代:1968

数据来源: WILEY

摘要:

AbstractMeasurements of the optical absorption spectra of the sublimed films of adenine, guanine, cytosine, thymine, and uracil were extended down to 120 mμ at room temperature. Several remarkable absorption peaks were found to exist below 190 mμ in addition to the already known ones near 260 mμ and 200 mμ. The intensities of these peaks were comparable to or, in some cases, even larger than those near 260 mμ and 200 mμ. It was found that the relative intensities of the absorption peaks differed considerably from sample to sample for all five bases, probably due to variation in the arrangement of the bases in the sublimed films. It was found also that the absorption spectra of the sublimed films change with aging on standingin vacuoat room temperature. On comparing the spectra of several fresh samples it was found that the intensities of the transitions with wavelength longer than 160 mμ of adenine, guanine, and uracil films are inversely correlated with those of the transitions shorter than

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060104

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe one‐dimensional Ising model, with nearest‐neighbor correlations only, used earlier in equilibrium studies of melting of DNA is extended to study the relaxation kinetics of copolymeric synthetic DNA near the melting temperature. An exponential kinetics, in agreement with the observations, has been fo

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060105

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe d.c. electrical conductivity of solid gels of bovine plasma albumin, under high vacuum, shows a semiconductive behavior which is sensitive to small amounts of complexed carcinogens and related compounds. The effect of these compounds on the electrical properties of the protein provides evidence of an interaction which may be related to the carcinogenic activity.

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060106

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe synthesis of polymers containingO‐tert‐butyl‐L‐serine,O‐tert‐butyl‐DL‐serine,L‐serine, andDL‐serine is reported. TheN‐benzyloxycarbonyl‐(LorDL)‐serine benzyl ester was used to synthesize the correspondingN‐benzyloxycarbonyl‐O‐tert‐butyl‐(LorDL)‐serine benzyl ester. Catalytic hydrogenation of this material gaveO‐tert‐butyl‐(LorDL)‐serine. The reaction ofO‐tert‐butyl‐(LorDL)‐serine with phosgene produced the correspondingN‐carboxyanhydrides. The kinetics of polymerization ofN‐carboxyanhydrides were investigated to facilitate, the preparation of block copolymers. TheO‐tert‐butyl blocking group was removed from polymers by treatment with HCl and HBr in benzene. Both high molecular weight (water‐insoluble) and low molecular weight (water‐soluble) homopolymers have been prepared, as well as water‐soluble

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060107

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe electrophoretic mobilities of adsorbed yeast ribonucleic acid have been measured as functions of pH, ionic strength, and biopolymer concentration and the results so obtained have been critically compared with those for adsorbed DNA. Like DNA, ribonucleic acid has also been found to reverse the positive charge of alumina owing to its adsorption on the solid‐liquid interface. The mobilities of adsorbed RNA have been found to be less than those of adsorbed DNA under identical conditions. The observed mobilities of adsorbed heat‐ and alkali‐denatured RNA are significantly less than those of adsorbed native RNA at a given pH and ionic strength of the medium. The electrophoretic mobilities as observed also show the evidence of RNA adsorption on the negatively charged surface of Dowex‐50 resin, but practically no adsorption of RNA on the negatively charged glass surface has been pr

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060108

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe streaming birefringence and extinction angles of DNA from T2 bacteriophage in neutral aqueous buffers have been determined over a range of concentrations from 5 to 44 μg./ml. and of velocity gradients from 5 to 50 sec.−1. Although the extinction angles are relatively small even at the lowest velocity gradients and concentrations studied, a lower limit estimate of the limiting extinction angle to shear rate ratio can be made, and this value is interpreted in terms of available dynamical theory. The statistical segment length has been estimated from the birefringence data as ∼ 1100 A. This figure is in satisfactory agreement with the results of independent calculations by ot

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060109

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

年代:1968

数据来源: WILEY

摘要:

AbstractA treatment of the Finite one‐dimensional Ising model is given in which four possible nearest‐neighbor interactions are taken into account, as well as the effect of the absence of neighbors at the ends of the chain. This represents the most general situation possible when interactions are limited to nearest neighbors and when the number of accessible states of a single residue is two. Some previous treatments of the Ising model are shown to be special cases of this problem. From the symmetry of the partition function it is found that the equilibrium transition curves for chains of all lengths intersect at their midpoints if and only if the free energy of both residue states is modified to the same extent when located at an end of the chain. The shift in transition midpoints with chain length generally observed for various one‐stranded systems is thus largely a measure of an end effect, and not a junction effect, as might seem to be the case from the theory of helix–coil equilibria. These considerations appear to be important in thecis—transequilibrium in poly‐L‐proline, where the observations of Engel on short‐chain samples suggest that the effects at junctions and at chain ends must differ significantly. It is concluded from his observations that acisunit at the end of a chain has a less favorable free energy than atransunit at the end. This is attributed to the fact that there are no van der Waals contacts between three residues at the end of the relatively compactcishelix and the missing adjacent turn of the helix, while the residues in the relatively opentranshelix are little affected by their location at the e

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060110

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

年代:1968

数据来源: WILEY

摘要:

AbstractCopolymers of ribocytidylic acid (C) and ribouridylic acid (U) with C contents of 66.5and 43 mole‐% have been prepared. Ultraviolet, absorption measurements were made of aqueous solutions of the mixtures of these copolymers (poly CU) and polyriboinosinic acid (poly I). In every set of examinations, a maximum hypochromicity (at 230, 248, or 260 mμ) was observed when the solution contained equal moles of C residue in the copolymer and I residue in the homopolymer. This fact was interpreted as indicating that a helix‐with‐loops structure, similar to that proposed by Fresco and Alberts7, is formed. It was shown that this structure is formed more rapidly and melts more sharply than that observed by Fresco and Alberts. An infrared examination was also made of this “helix‐with‐loops” structure. It was found that a few absorption bands are assignable to the helix part and a few other bands to the loop part of

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060111

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

年代:1968

数据来源: WILEY