bluuebunny/crossref_metadata_2025_split huggingface dataset:
Viscosity study of DNA
Authors: Scruggs Robert L. , Ross Philip D. 
Published: December 2004

AbstractThe intrinsic viscosity of DNA (salmon sperm, calf thymus, T4 phage) in the presence of univalent cations decreases in a continuous manner as the ionic strength is increased and then attains a characteristic limiting value for each cation. Between 0.1 and 0.5M the intrinsic viscosity is independent of cation, while at high salt concentration the order of decreasing limiting viscosity is K+, Na+, Li.+ The intrinsic viscosity of T4 bacteriophage DNA decreases with increasing Mg++ concentration and in 0.1M MgCl2 attains a value one‐half of that found in 0.2M NaCl. Slightly beyond 0.1M MgCl2 spontaneous growth of birefringent fibers takes place, and upon further addition of Mg++ these fibers redissolve to form a transparent gel of higher viscosity. The observed Huggins' constants pass through a maximum with increasing salt concentration for all of the ions studied. It is demonstrated that the concentration dependence of the reduced viscosity may be abolished and regenerated by the introduction and removal of trace amounts of basic proteins, polypeptides and polyamines. The viscosity behavior observed with the deliberately contaminated DNA samples resembles most of that reported in earlier viscosity studies, indicating that a large body of previous work on DNA probably was performed on impure material.
Polymerization of N‐carboxyanhydrides of 1‐aminocycloalkanecarboxylic acids
Authors: Frankel Max , Bachi Mario David 
Published: December 2004

AbstractThe polymerizations of the N‐carboxyanhydrides of 1‐aminocyclopropanecarboxylic acid, 1‐aminocyclobutanecarboxylic acid, 1‐aminocyclopentanecarboxylic acid, and 1‐aminocyclohexanecarboxylic acid were investigated. These N‐carboxyanhydrides did not polymerize in bulk when heated to their melting points under reduced pressure. In solution, they polymerized extremely slowly on initiation with n‐hexylamine and relatively slowly when initiated by sodium methoxide–methanol. The polymerization rates of the above NCAs in dimethyl sulfoxide solution, initiated by sodium methoxide–methanol were found to increase in the following order: NCA of 1‐aminocyclohexanecarboxylic acid, NCA of 1‐aminocyclopropanecarboxylic acid, NCA of 1‐aminocyclopentanecarboxylic acid and NCA of 1‐aminocyclobutanecarboxylic acid. The influence of the alicyclic side rings on the relative rates of polymerization of the respective NACs is considered.
Crosslinked synthetic polypeptides. II. Evaluation of the internal structure of intramolecularly crosslinked polymers by polarization of fluorescence measurements
Authors: Gill Thomas J. 
Published: December 2004

AbstractThe introduction of intramolecular amide bonds into synthetic polypeptides produces molecules with organized spatial structure which are good models for the tertiary structure of proteins. Polarization of fluorescence measurements were used to study the internal structure and the overall rigidity of the intramolecularly crosslinked polypeptides. The graph of [(1/p) + (1/3)] against T/η changes from a straight line to a continuous curve: the temperature at which this change occurs and the slope of the straight line segment measure the stability of the internal structure of the molecule. The introduction of one to six crosslinks produces an organized internal structure that becomes more stable as the number of crosslinks increases. In contrast to the fluorescence measurements, the intrinsic viscosities, reflecting the overall hydrodynamic domain of the molecules, change (decrease) to the same extent whether one, four, or six intramolecular crosslinks are present. The overall rigidity of the polymers can be assessed by the rotational relaxation time ρh and the polarization at 10°C. p10. Both of these criteria show that the presence of six crosslinks significantly increases the rigidity, but one or four does not. The various hydrodynamic measurements may be fitted into a hierarchy of discrimination: intrinsic viscosity, sedimentation, and diffusion for size and shape; rotational relaxation time and polarization of fluorescence at a given temperature for overall molecular rigidity; and transition temperature and rate at which it is attained for internal molecular detail.
Determination of the dominant factors which influence the net hydration of native sodium deoxyribonucleate
Authors: Hearst John E. 
Published: December 2004

AbstractA theory for the dependence of the net thermodynamic solvation of a macroion in an electrolyte solution is presented. The solvation in moles salt/mole macroion is shown to approach – |Zp|/v in the limit of infinite dilution of salt and macroion. The solvation in moles water/mole macroion is shown to approach zero at zero water activity. Isopiestic determinations of the hydration of sodium deoxyribonucleate in NaCl, Na2SO4, and NaClO4 solutions indicate that short‐range interactions of the NaDNA with solvent account for more than half of the observed solvation. The net hydration appears to be predominantly influenced only by water activity.
Interactions of metal ions with polynucleotides and related compounds. III. Degradation of polyribonucleotides by lanthanum ions,
Authors: Eichhorn Gunther L. , Butzow James J. 
Published: December 2004

AbstractThe polyribonucleotides of adenylic, cytidylic, and uridylic acids are degraded in a 2‐hr. period at 64°C. into low molecular weight oligonucleotides and mononucleotides through the action of lanthanum (III) or other trivalent inner transition metal ions. Polyinosinic acid is degraded somewhat more slowly. Cleavage of the polynucleotide chains occurs at the 5′‐phosphate linkages. The 3′‐mononucleotides produced require over 100 hr. of further heating at 64°C. to produce nucleoside and orthophosphate. The reaction between lanthanum (III) and the polynucleoside involves one metal ion for every three nucleotide residues, with each metal ion apparently chelated to a 2′‐hydroxyl and a phosphate group and bound to only one polynucleotide chain.
Interactions of metal ions with polynucleotides and related compounds. IV. Degradation of polyribonucleotides by zinc and other divalent metal ions,
Authors: Butzow James J. , Eichhorn Gunther L. 
Published: December 2004

AbstractPolyadenylic acid is degraded into mononucleotides and low molecular weight oligonucleotides in a 20 hr. period at 64°C. by the action of Mn (II), Co (II), Ni (II), and Cu (II) ions, and in a 2 hr. period by Zn (II) ions. The latter also degrade poly C, poly U, and RNA at approximately the same rate, but poly I is degraded very much more slowly. No such difference in reaction rates can be observed in the alkaline degradation of polynucleotides. The sluggishness of the reaction with poly I is not due to any highly ordered structure of the zinc–poly I complex, but probably to the weakening of the zinc–phosphate bond through simultaneous binding of the zinc to the inosine base. Evidence for such a hypothesis is derived from the inhibition of the zinc degradation of poly A by inosinic acid or poly I. No drastic difference in the nucleotide composition of the undegraded residue can be observed in the degradation of RNA by zinc and by alkali.
Conformation of polyriboadenylic acid: pH and temperature dependence
Authors: Holcomb D. N. , Tinoco I. 
Published: December 2004

AbstractEvidence is presented that polyriboadenylic acid (Poly A) is a single‐strand flexible helix of stacked bases at neutral pH and room temperature. As the temperature is raised the stacking decreases, but there is still perceptible order at 80°C. The thermal transition from the double‐strand helix (which exists at low pH) to the single‐strand helix has been followed by optical rotatory dispersion, optical absorption, and viscosity measurements.
Theoretical determination of sterically allowed conformations of a polypeptide chain by a computer method
Authors: Némethy George , Scheraga Harold A. 
Published: December 2004

AbstractA mathematical method has been developed, together with a digital computer program for its evaluation, for the determination of possible conformations of a polypeptide chain for any given amino acid sequence. Allowed conformations were required to satisfy predetermined criteria regarding the locations of potential energy minima for rotation around single bonds, steric restrictions arising from van der Waals contacts between atoms, and the formation of a closed polypeptide loop by means of a peptide linkage or a disulfide bridge. Requirements for specific noncovalent interactions can also be considered. Various assumptions regarding the selection of the minima for rotational potentials and of the van der Waals contact distances are discussed. According to the assumptions adopted in the paper, 21 conformations are allowed for a glycine residue which is part of a dipeptide. These conformations are assumed to lie at minima of the rotational potential function, and satisfy simultaneously the steric requirements. Dipeptides containing alanine or other residues are restricted to 7 such conformations. As an example of the applicability of the method, the computation was performed for the smallest loop containing a disulfide bridge in the ribonuclease molecule, i.e., the cyclic octapeptide formed by residues 65 to 72. Only 15 allowed conformations were found for the loop as a whole. Parameters characterizing these allowed conformations are tabulated. Approximate calculations indicate the importance of steric restrictions and of the presence of side chains in reducing the conformational freedom of this peptide. Further potentialities of the method are discussed.
Kinetics and equilibria in the acid denaturation of deoxyribonucleic acids from various sources
Authors: Bunville L. G. , Geiduschek E. P. , Rawitscher M. A. , Sturtevant J. M. 
Published: December 2004

AbstractThe acid denaturation of a variety of DNA‡ samples with guanine–cytosine (GC) contents ranging from 37–64% has been investigated by means of potentiometric, spectrophotometric, and thermal titrations, including spectrophotometric titrations in a stopped‐flow fast reaction apparatus. As the pH of a solution of native DNA is lowered from the neutral range the net charge on the molecule becomes more positive as a result of the addition of protons to the bases adenine, cytosine, and to a lesser extent guanine. At a fairly sharply defined value of the charge a conformational transition sets in which is completed after the charge has increased in the positive direction by an additional 0.4–0.5 unit per base pair. The threshold value of the charge is dependent on the composition of the DNA as well as various experimental parameters such as temperature and ionic strength. At 25°C. in 0.1M NaCl the threshold value is approximately 0.55 charge unit per base pair relative to pH 6 for a GC content of 37% and 0.78 for 64% CG. The conformational transition is accompanied by heat absorption amounting, in the case of salmon DNA in 0.1M NaCl, to 3020 ± 150, 4920 ± 200, and 5700 ± 250 cal./mole of base pairs at 5, 25, and 45°C., respectively. If it is assumed that the heats of ionization of the bases are the same in denatured DNA as in the isolated nucleotides, the result at 25° C. can be corrected by using previously determined heats of ionization to give for the hypothetical process, DNA (native, pH 6) → DNA (denatured, pH 6) ΔH = 8300 cal./mole of base pairs. ΔH appears to be independent of DNA composition, an average value of 8000 cal./mole of base pairs being obtained for DNA samples having GC contents ranging from 37–64%. The calorimetric results are consistent with the view that hydrophobic interactions are important in the stabilization of the DNA double helix. The kinetics of the acid denaturation of salmon DNA is complex.
Interactions between trinucleotides: The electrostatic contribution and its possible relation to the mechanism of translation of the genetic code
Authors: Nash H. A. , Bradley D. F. 
Published: December 2004

AbstractThe coulombic interaction between pairs of trinucleotides has been computed from quantum theory. The results are discussed in terms of their relation to hydrogen bonds and stacking in such systems and to the mechanism by which messenger RNA codons recognize transfer RNA nodocs.
Effect of different solvent systems on the aggregation and conformation of S‐carboxymethyl bovine serum albumin
Authors: Harrap B. S. , Woods E. F. 
Published: December 2004

AbstractThe aggregation properties of S‐carboxymethyl bovine serum albumin (SCM‐BSA) have been shown to be greatly influenced by the presence of thioglycollide esters in the thioglycollic acid used as a reducing medium. Pure thioglycollic acid gives a product which is aggregated at both pH 7 and 9. Disaggregation may be effected by sodium dodecyl sulfate, by covalently linking groups on to the molecule in order to increase the net negative charge, and solvents such as 8M urea, 14M formamide, 11.5M acetic acid, formic acid, and 2‐chloroethanol. The mechanisms underlying disaggregation in these widely differing solvents are discussed. The results confirm previous findings of a single polypeptide chain in serum albumin. The optical rotatory dispersion of BSA and SCM‐BSA have been compared in a variety of solvents. It has been shown that the disulfide crosslinks in BSA are not the limiting factor to α‐helix formation.
Conformation changes in the nonionizable water‐soluble synthetic polypeptide poly‐N5‐(3‐hydroxypropyl) ‐L‐glutamine
Authors: Lupu‐Lotan Noah , Yaron Arieh , Berger Arieh , Sela Michael 
Published: December 2004

AbstractPoly‐N5‐(3‐hydroxypropyl)‐L‐glutamine (PHPG) samples of molecular weights from 20,000 to 140,000 were synthesized by the action of 3‐amino‐1‐propanol on poly‐γ‐benzyl‐L‐glutamate. PHPG is freely soluble in water and in a variety of organic solvents and was shown to be devoid of functional groups ionizing in the pH range 2–12. From hydrodynamic data (viscosity, sedimentation, diffusion) and optical rotatory measurements (ORD in the range 289–650 mμ, circular dichroism and Cotton effects in the range 210–280 mμ) on samples of different molecular weight it was concluded that PHPG is largely helical in methanol, ethylene glycol, formamide, dimethylform‐amide, n‐butylamine, and acetic acid, and randomly coiled in dichloroacetic acid and formic acid. In water the polymer is partly helical, the degree of helicity increasing with decreasing temperature and increasing molecular weight. The following solutes were found to decrease the helicity in the order indicated: NaOH > guanidinium chloride > urea > HCl > LiBr > NaBr > NaCl > H2O. Detergents do not destroy the helical conformation. Helix–coil transition curves were obtained for the solvent pairs: methanol–water, acetic acid–water, and chloroform–dichloroacetic acid. Thermal transitions were observed in water, water–methanol (70:30 v/v), and dichloroacetic acid–ethylene dichloride (22:78 v/v), the latter being of the “inverted” type. Heats of helix formation were calculated and their significance is discussed.
Electrochemical observations in microbiological processes. Growth of Thiobacillus thiooxidans. I
Authors: Fischer David J. , Herner Albert E. , Landes Alma , Batlin Alex , Barger John W. 
Published: December 2004

AbstractThe growth of Thiobacillus Thiooxidans, utilizing sulfur in three media, was studied by observing changes in halfcell emf, bacterial cell count, and acid production, all as a function of time. A comparison of the biological halfcell emf with comparable control halfcells reveals that T. thiooxidans makes an electrochemical contribution to halfcell voltage. A change from the more complex medium of Skerman's mineral salts to ATCC allowed a clearer delineation of the ability of T. thiooxidans to make an electrochemical contribution. Reproducible biological halfcell emf's were obtained when the ferrous sulfate was removed from the ATCC medium. One halfcell, consisting of T. thiooxidans utilizing sulfur in ATCC, was observed over a 111‐day period. During this time, the initial halfcell voltage of −0.35 V. decreased to a value of −0.64 V. (hydrogen emf series). T. thiooxidans, in utilizing sulfur, produces only sulfate ion, thereby simplifying the identification of an electrochemical contribution during growth.
Electrochemical observations in microbiological processes. Growth of Thiobacillus Thiooxidans. II
Authors: Fischer David J. , Landes Alma , Sandford Maxwell T. , Herner Albert E. , Wiegand C. J. Wesley 
Published: December 2004

AbstractThe electrochemical activity of the individual chemicals in the nutrient medium for growth of Thiobacillus thiooxidans was studied along with the effect of the gases in equilibrium with their solutions. Several chemicals were active individually; however, the magnitudes, as measured by changes in half‐cell potential, were less than that observed when T. thiooxidans was present in their composite mixture. Sterilized Skerman's mineral salts and the American Type Culture Collection (without ferrous sulfate) media were not sensitive electrochemically to changes from pure oxygen to nitrogen atmospheres. When T. thiooxidans was present in these media, the biological half‐cell emf became sensitive to changes in the oxygen content of the atmosphere in equilibrium with the organism and nutrient. The ability of T. thiooxidans to make an electrochemical contribution, as registered by a platinum electrode, is substantiated further by these investigations.
Gas absorption in a stirred vessel: Locale of transfer action
Authors: Wilhelm R. H. , Donohue W. A. , Valesano D. J. , Brown G. A. 
Published: December 2004

AbstractBy means of gas‐absorption experiments in a stirred vessel, with various depths of liquid above a properly positioned single‐opening pipe‐type gas sparger, conclusions are reached about relative contributions to the overall absorption rate by localized actions near the sparger tip, in the impeller region, and from bubbles distributed in the bulk volume of the fluid. Results are discussed for difficulty soluble gases (oxygen in water and chlorine in water) and a substantially soluble gas (chlorine in benzene). In all cases, dissolution rates in the vicinity of the sparger and impeller were significantly large compared with those near free bubbles.
Oxygen‐absorption rate‐controlled feeding of substrate into aerobic microbial cultures
Authors: Hospodka Jaroslav 
Published: December 2004

AbstractA system of automatic control of substrate inflow into an aerated culture of microorganisms which depend on oxygen‐absorption rate (OAR) has been devised and tested. As the control variable, dissolved oxygen concentration (DOC), which shows the equilibrium between OAR and oxygen‐uptake rate in the microbial culture, was chosen. If the equilibrium is disturbed by changes in OAR, then the oxygen‐uptake rate is changed by substrate limitation. The DOC is measured by means of a Clark‐type polarographic electrode, and the signal is used to actuate the substrate inflow valve or pump. The oxygen‐uptake rate changes of microorganisms, after the addition or exhaustion of substrate in the medium, are so rapid that they can be used for this type of control.Fundamental equations were derived and graphical solutions for the control system parameters were suggested for the steady‐state relations between DOC, oxygen‐uptake rate, specific growth rate, substrate concentration, KLa, and concentration of microorganisms. The system is stable in the entire range of the uptake rates up to nearly the maximum attainable in unlimited substrate conditions, and can be operated in batch feed or continuous flow modifications. It was experimentally tested with the yeast Saccharomyces cerevisiae. The complete utilization of aeration‐system capacity of the fermentor was achieved with high yeast yield and no alcohol formation. The quality of the product was excellent.
Microflotation: New low gas‐flow rate foam separation technique for bacteria and algae
Authors: Rubin Alan J. , Cassel E. Alan , Henderson Oliver , Johnson J. Donald , Lamb James C. 
Published: December 2004

AbstractFoam separation of microorganisms has been investigated with varying success by many workers, usually at high rates of gas flow. Microflotation was developed to overcome some of the disadvantages inherent in these high gas‐flow‐rate processes and is introduced in this paper as a new technique for the foam separation of microorganisms at low gas‐flow rates. With microflotation, a stable surface phase is produced by adding an insoluble collector such as a long‐chain fatty acid or amine. The formation of an insoluble surface phase eliminates the need for high foaming. Low rates of gas flow are used resulting in a more efficient separation and a less voluminous and drier surface phase upon which to collect the microorganisms. The efficiency of this technique is also improved by using flotation aids such as frothers and flocculents. Frothers are used to improve the collector properties of the surfactant and to refine further the small bubbles produced by a very fine sparger. Small concentrations of flocculents, such as alum, are used to partially agglomerate the organisms and provide sites for adsorption of collector. The work described in this paper is preliminary in nature, designed to illustrate that a low flow‐rate process may be used to separate microorganisms and to stimulate further research. The applications discussed are removal of the bacterium, Escherichia coli, and alum, and two species of algae, Chlamydomonas reinhardtii and Chlorella ellipsoidea, using stearylamine without alum. The frother used was ethanol.
Sterilization of tissue‐culture medium by filtration on a large laboratory scale
Authors: Telling R. C. , Stone C. J. , Maskell M. A. 
Published: December 2004

AbstractThe design and operation of a permanently‐piped plant for sterilizing 10–200 l. of tissue‐culture media is described. The plant is sterilized in situ by steam injection, the filtration rate is 2–3 l./min., and the turn‐around time for volumes of 100 l. is about 3 hr.
Characteristics of hydrogen bacteria
Authors: Repaske Roy 
Published: December 2004

AbstractA brief review of the development of our knowledge about hydrogen bacteria is presented, with emphasis on the characteristics and physiological differences of various Hydrogenomonas species. One species, Hydrogenomonas eutropha, is discussed in greater detail. Nutritional requirements, physical factors affecting growth, and equipment used for culturing 100‐ml. shake cultures and 15‐1.mass cultures of H. eutropha are described. Cell‐free extracts of H. eutropha carry out the oxyhydrogen reaction as demonstrated by the alternate reduction and oxidation of endogenous flavins and cytochromes by molecular hydrogen and oxygen, respectively. Spectra of cell‐free extracts of this organism show the presence of cytochromes of the c and b1 types. A cytochrome of the o type was also found, but none of the a cytochromes were detected. The sum of a series of enzymatic reactions shown to be catalyzed by these extracts can account for the oxidation of hydrogen by oxygen.
A chemically defined fermentation medium for the growth ofMicromonospora purpurea
Authors: Wagman G. H. , Weinstein M. J. 
Published: December 2004

AbstractA chemically defined medium forMicromonospora purpureahas been devised, consisting of glucose, a nitrogen source, calcium carbonate, magnesium sulfate, dibasic potassium phosphate, and the required trace quantities of iron, copper, zinc, and manganese. Using washed cell inocula, dry mycelial weights of more than 16 mg./ml. were obtained in 7‐day shaken‐flask fermentations. Nutrient requirements forM. purpureaare discussed and growth data presented. Sucrose, maltose, starches and dextrins could be substituted for glucose, and resulted in good growth of the organism. A number of amino acids and inorganic nitrogen‐containing compounds were capable of utilization as sole nitrogen sources. Weekly serial transfers of the culture in defined medium have shown no diminution in mycelial weights over a four‐month period.