bluuebunny/crossref_metadata_2025_split huggingface dataset:
COMPARATIVE STUDIES OF THREE METHODS FOR MEASURING PEPSIN ACTIVITY
Authors: Loken Merle K. , Terrill Kathleen D. , Marvin James F. , Mosser Donn G. 
Published: May 2004

Comparison has been made of a simple method originated by Absolon and modified in our laboratories for assay of proteolytic activity using RISA (radioactive iodinated serum albumin—Abbott Laboratories), with the commonly used photometric methods of Anson and Kunitz. In this method, pepsin was incubated with an albumin substrate containing RISA, followed by precipitation of the undigested substrate with trichloroacetic acid and measurement of radioactive digestion products in the supernatant fluid.
The I131—albumin bond was shown in the present studies to be altered only by the proteolytic activity, and not by the incubation procedures at various values of pH. Any free iodine present originally in the RISA was removed by a single passage through a resin column (amberlite IRA-400-C1).
Pepsin was shown to be most stable in solution at a pH of 5.5. Activity of pepsin was shown to be maximal when it was incubated with albumin at a pH of 2.5. Pepsin activity was shown to be altered in the presence of various electrolytes. Pepsin activity measured by the RISA and Anson methods as a function of concentration or of time of incubation indicated that these two methods are in good agreement and are equally sensitive. Consistently smaller standard errors were obtained by the RISA method of pepsin assay than were obtained with either of the other methods.
STUDIES ON THE ORIGIN OF BACTERIAL VIRUSES
Authors: Northrop John H. ,   With the Technical Assistance of Marie King
Published: May 2004

The growth rates, the mutation frequency rate constants of the terramycin-resistant cells, the burst size of the phage-producing cells, and the ratio of phage to cells all have a temperature coefficient of about 2 from 20 to 35° (µ = 9 x 103 calories), with a maximum at 40°.
The mutation frequency rate constant (or time rate constant) of the phage-producing cells increases from 20 to 45° with a temperature coefficient of about 3 (µ = 2 to 3 x 104 cal.).
The change in the values for the growth rate, mutation rate, and cell volume occurs in less than 1 hour, after the temperature is changed. The value for the burst size of phage-producing cells changes for 3 to 4 hours.
Prolonged growth of megatherium 899 at 48 to 50° results in the production of C + S phage, in place of T. Returning the culture to 25° results in the production of small T phage.
PREPARATION OF THROMBOKINASE FROM BOVINE PLASMA
Authors: Milstone J. H. 
Published: May 2004

Thrombokinase is prepared from bovine plasma by a procedure involving: treatment with diatomaceous silica, adsorption on barium sulfate, flowing elution with two successive phosphate buffers, ammonium sulfate fractionation, "spontaneous" activation in concentrated solution, and isoelectric precipitation. The yield of nitrogen is 0.002 per cent, corresponding to 1.2 mg. protein per liter of plasma.
When diluted back to the volume of parent plasma, and complemented by calcium plus cephalin, the product causes appreciable activation of prothrombin in 1 minute. Thus, the quantity of thrombokinase obtainable is compatible with a physiologic role. In the more complex system used for routine assay, thrombokinase can be supplied by crude plasma at a dilution of 1/500. In parallel tests, the product appears to be more active than its parent plasma, although it contains only 0.002 per cent of the nitrogen. However, the thrombokinase of the product has been activated, whereas the thrombokinase of the plasma is probably in an inactive precursor state.
When diluted back to the volume of parent plasma, to a concentration of 0.2 microgram nitrogen per ml., thrombokinase can slowly activate prothrombin in the presence of oxalate, and without the addition of accessory factors. Activation of prothrombin in the presence of oxalate is faster with higher concentrations of thrombokinase.
PHOTOREACTIONS IN PHYCOMYCES
Authors: Cohen R. , Delbrück M. 
Published: May 2004

Sporangiophores of Phycomyces in stage IV b have been stimulated by parallel light in test areas 0.2 mm. wide.
The growth responses to large stimuli are very large, owing probably to light scattered within the specimen. For medium stimuli the sensitive zone coincides with the growth response zone obtained previously and excludes the region of maximum stretch.
Sustained stimulations were used to elicit tropic responses. The bends formed travel away from the sporangium at a speed equal to the growth speed. Thus they remain very close to the stimulus when this is held at a constant level relative to ground but separate from it for stimuli programmed differently.
The existence of a protoplasmic structure, the "inner wall," with the following properties is postulated: it is attached to the lower, non-growing part of the sporangiophore and grows by addition above the sensitive zone. It neither stretches nor twists in the sensitive zone. It is the seat of the light receptors and gives growth and tropic responses. The cell wall follows its bends by elastic stretch.
THE INHIBITORY EFFECT OF STROPHANTHIDIN ON SECRETION BY THE ISOLATED GASTRIC MUCOSA
Authors: Cooperstein I. L. 
Published: May 2004

The unidirectional fluxes of Na+ and Cl- were measured across the isolated gastric mucosa of the bullfrog (R. catesbiana). The addition of strophanthidin, a cardiac aglycone, resulted in marked reductions of the spontaneous potential and short-circuit current. Associated with these changes, the isolated gastric mucosa ceased secreting chloride and hydrogen ion. Although the active component of chloride transfer was inhibited, the exchange diffusion component seemed to increase. No significant changes in membrane conductance or sodium flux were noted.
Possible mechanisms of strophanthidin inhibition were discussed in view of its effect on chloride transport across the gastric mucosa and on sodium and potassium transfer in other tissues. It was concluded that the cardiac glycosides may not be specific inhibitors of sodium and potassium transport. This non-specific inhibition suggests that active chloride transport is affected by strophanthidin directly and/or anion secretion is dependent upon normal functioning of cation transport systems in the tissue.
THE RESPONSES OF LIMULUS OPTIC NERVE FIBERS TO PATTERNS OF ILLUMINATION ON THE RECEPTOR MOSAIC
Authors: Ratliff Floyd , Hartline H. K. 
Published: May 2004

The inhibition that is exerted mutually among receptor units (ommatidia) of the compound eye of Limulus is less for units widely separated than for those close together. This diminution of inhibition with distance is the resultant of two factors: (1) the threshold of inhibitory action increases with increasing distance between the units involved; and (2) the coefficient of inhibitory action decreases with increasing distance.
The discharge of nerve impulses from ommatidia at various distances from one another may be described quantitatively by a set of simultaneous linear equations which express the excitatory effects of the illumination on each ommatidium and the inhibitory interactions between each ommatidium and its neighbors. The values of the thresholds and coefficients of inhibitory action, which appear as parameters in these equations, must be determined empirically: their dependence on distance is somewhat irregular and cannot yet be expressed in an exact general law. Nevertheless the diminution of inhibitory influences with distance is sufficiently uniform that patterns of neural response generated by various patterns of illumination on the receptor mosaic can be predicted qualitatively. Such predictions have been verified experimentally for two simple patterns of illumination: an abrupt step in intensity, and a simple gradient between two levels of intensity (the so-called Mach pattern). In each case, transitions in the pattern of illumination are accentuated in the corresponding pattern of neural response.
Electrical Characteristics and Activation Potential of Bufo Eggs
Authors: Maéno Takashi 
Published: May 2004

Electrical characteristics and their changes during activation were studied with the microelectrodes on the oocytes and eggs of the toad, Bufo vulgaris formosus Boulenger.
In young oocytes, the membrane characteristics had some similarities to those of nerve and muscle, except for a relatively large resistance of 25 KΩcm.2 and an absence of the action potential in the former. After maturation, however, the membrane characteristics became entirely different from those of oocytes and other excitable tissues. In the mature eggs the membrane resistance was measured to be as high as 200 KΩcm.2, and no specific permeability of the membrane to potassium ions was observable.
A slow monophasic change in the membrane potential was recorded in every activation produced by mechanical stimulation, and termed "activation potential." In fresh water, its amplitude was as large as 80 to 90 mv. with an overshoot of about 50 mv. The activation potential might be comparable to the action potential of nerve and muscle, but was fundamentally different in ionic mechanism from the latter, since the former was caused by a marked increase in permeability to chloride ions.
The Dimensions of the Extracellular Space in Sartorius Muscle
Authors: Tasker Patricia , Simon Shirley E. , Johnstone B. M. , Shankly K. H. , Shaw F. H. 
Published: May 2004

A survey has been made of the amount of muscle water available to inulin, sucrose, and radioiodinated human serum albumin (RISA). The percentage spaces available to the three molecules are of the same order of magnitude, but the sucrose space &gt; inulin space &gt; albumin space. The kinetics of influx and efflux of RISA have been studied, and it appears that a small part of the albumin may be adsorbed in the extracellular phase. Nevertheless the albumin space would appear to give the best index of the extracellular volume.
The scatter in values found for the extracellular space by all methods is very great, ranging from 8 to 40 per cent and renders invalid the use of a mean value for the calculation of intracellular concentrations. The variation within paired muscles is less than between pairs, provided the tissue has undergone no volume change. Increase in total muscle volume when the muscle is placed in a hypotonic solution leads to a decrease in the size of the extracellular space.
The Mechanism of Dual Responsiveness in Muscle Fibers of the Grasshopper Romalea microptera
Authors: Cerf J. A. , Grundfest H. , Hoyle G. , McCann Frances V. 
Published: May 2004

Dually innervated Romalea muscle fibers which respond differently to stimulation of their fast and slow axons are excited by intracellularly applied depolarizing stimuli. The responses, though spike-like in appearance, are graded in amplitude depending upon the strength of the stimuli and do not exceed about 30 mv. in height. In other respects, however, these graded responses possess properties that are characteristic of electrically excitable activity: vanishingly brief latency; refractoriness; a post-spike undershoot. They are blocked by hyperpolarizing the fiber membrane; respond repetitively to prolonged depolarization, and are subject to depolarizing inactivation. As graded activity, these responses propagate decrementally.
The fast and slow axons of the dually responsive muscle fibers initiate respectively large and small postsynaptic potentials (p.s.p.'s) in the muscle fiber. These responses possess properties that characterize electrically inexcitable depolarizing activity. They are augmented by hyperpolarization and diminished by depolarization. Their latency is independent of the membrane potential. They have no refractory period, thus being capable of summation. The fast p.s.p. evokes a considerable or maximal electrically excitable response. The combination, which resembles a spike, leads to a twitch-like contraction of the muscle fiber. The individual slow p.s.p.'s elicit no or only little electrically excitable responses, and they evoke slower smaller contractile responses. The functional aspects of dual responsiveness and the several aspects of the theoretical importance of the gradedly responsive, electrically excitable component are discussed.
The Kinetics of the Distribution and Breakdown of I131-Albumin in the Rabbit
Authors: Reeve E. B. , Roberts J. E. 
Published: May 2004

Rabbit plasma albumin was labelled with I131, injected intravenously, and measurements were made of the radioactivity in plasma, urine, and feces over many days. In some experiments plasma radioactivity was fractionated into I131-albumin activity and that of labelled breakdown products. Curves of these radioactivities were compared with corresponding curves predicted by four mathematical models. Each model included a vascular and extravascular albumin compartment in transfer equilibrium, a radioactive breakdown products compartment, and an excretion compartment; but model A supposed I131-albumin catabolism to occur within the vascular system, model B within the extravascular compartment, model C within both, and model D within a separate compartment receiving albumin for catabolism from the plasma. The experimental data were reasonably well predicted by models A and C. However, model D, though data were insufficient for its complete validation, gave the best predictions and agrees with present knowledge of albumin catabolism.
Various methods for calculating the rate of albumin breakdown are discussed. When calculations are based solely on the plasma radioactivity data, identical rates are predicted by models A, C, and D. When, as a valuable independent method, catabolism is calculated from plasma and excreted radioactivities, an error (ordinarily small) is incurred unless account is taken of the rate of passage of I131-albumin to the breakdown sites, and of the rate of excretion of the radioactive breakdown products.
Evidences from Action Spectra for a Specific Participation of Chlorophyll b in Photosynthesis
Authors: Myers Jack , French C. S. 
Published: May 2004

Rate of oxygen evolution in photosynthesis was measured as the current from a polarized platinum electrode covered by a thin layer of Chlorella. The arrangement gave a reproducibly measurable rate of photosynthesis proportional to light intensity at the low levels used and gave rapid response to changes in illumination. Two phenomena have been explored.
The Emerson effect was observed as an enhancement of photosynthesis in long wavelength red light (700 mµ) when shorter wavelengths were added. Two light beams of wavelengths 653 and 700 mµ when presented together gave a photosynthetic rate about 25 per cent higher than the sum of the rates obtained separately.
Large and reproducible transients in rate of oxygen evolution were observed accompanying change in illumination between two wavelengths adjusted in intensity to support equal steady rates of photosynthesis. The transients were found not to be specifically related to long wavelength red light.
Both enhancement and the transients have identical action spectra which are interpreted as demonstrating a specific photochemical participation of chlorophyll b.
The Interaction of Dextran with Serum Albumin, Gamma Globulin, and Fibrinogen
Authors: Ponder Eric , Ponder Ruth V. 
Published: May 2004

The interaction between dextran and serum albumin, gamma globulin, and fibrinogen can be studied by an electrophoretic method, which depends on obtaining electrophoretic patterns, first of each protein, then of dextran, and finally of mixtures of each protein with dextran. The areas under the electrophoretic spikes for each protein, for dextran, and for the mixtures are measured.
At pH's between 9.6 and 6.6, there is a transference of albumin to dextran when the two components are mixed, the amount of albumin lost being nearly equal to the gain in the new component, albumin plus dextran. This new species has a specific refractive index of about 0.00205 and seems to be composed of about one albumin molecule for every four dextran molecules.
The method is unsuitable for studying interaction between dextran and gamma globulin because these substances are almost immobile and do not separate into two spikes.
The method shows that a mixture of dextran and fibrinogen gives only one slowly moving spike (pH 6.6 to 8.6), the area under which is the sum of the areas under the dextran and the fibrinogen spikes taken separately. Either there is no interaction, or the new species has virtually the same refractive index increment as fibrinogen and dextran taken separately (0.0014 to 0.0015).
Effect of the Method of Leading on the Recording of the Nerve Fiber Spectrum
Authors: Gasser Herbert S. 
Published: May 2004

A study has been made of the modifications of the shape of a nerve action potential dependent upon the placement of the two electrodes, always necessary for a lead. In a classic diphasic lead separation of the electrodes brings out, in addition to a separation of the phases, the appearance of a positive deflection traceable to the passage of an impulse between the electrodes. This phenomenon, called the lead separation effect (1.s.e.), must be considered as an expression of a feature of normal nerve fiber biophysics. It regularly appears and it can be analyzed with respect to the position of the sink maximum. Also it cannot be eliminated by a block at the second electrode.
The advantage of approximating the leads was shown by the absence of a 1.s.e. following spikes recorded by electronic integration of tangents, which with validity can be derived from threshold fibers. Since tangent leads are not adaptable to recording a spectrum, a block at the second electrode is required. The making of such blocks and the configuration of records obtained with them are described. Conditions for an optimal lead, but not an ideal lead, were delimited. In an optimal lead only two major elevations appear in the spectrum of a skin nerve: those known as alpha and delta. A reference to maps of fiber size analyses shows that the fibers in the delta elevation have velocities of conduction slower than they would have if following in linear sequence the fiber diameters belonging to the alpha elevation.
Liquid Junction and Membrane Potentials of the Squid Giant Axon
Authors: Cole Kenneth S. , Moore John W. 
Published: May 2004

The potential differences across the squid giant axon membrane, as measured with a series of microcapillary electrodes filled with concentrations of KCl from 0.03 to 3.0 M or sea water, are consistent with a constant membrane potential and the liquid junction potentials calculated by the Henderson equation. The best value for the mobility of an organic univalent ion, such as isethionate, leads to a probably low, but not impossible, axoplasm specific resistance of 1.2 times sea water and to a liquid junction correction of 4 mv. for microelectrodes filled with 3 M KCl.
The errors caused by the assumptions of proportional mixing, unity activity coefficients, and a negligible internal fixed charge cannot be estimated but the results suggest that the cumulative effect of them may not be serious.
Calcium and Strontium in Rat Small Intestine Their Fluxes and Their Effect on Na Flux
Authors: Dumont P. A. , Curran Peter F. , Solomon A. K. 
Published: May 2004

Studies have been carried out on movements of Ca and Sr ions in rat small intestine, using the in vivo preparation developed by Curran and Solomon (5). In the concentration range of 0 to 25 mM, Sr flux appears to be passive, though restricted. Ca transport may not, however, be ascribed to passive independent movement of these ions since at higher concentrations (12.5 and 25 mM) Ca return from blood to intestinal lumen increases more than expected. An apparent diffusion coefficient of Ca and Sr ions in the membrane has been calculated and the influence of negative charges within the membrane on cation diffusion has been examined in a semiquantitative manner.
Both Ca and Sr ions exercise a drastic effect on active Na absorption from intestine and on concomitant passive water movement. From 0 to 1 mM, Ca and Sr ions cause a sharp increase in Na and water efflux from the lumen. This rising phase is interpreted in terms of combination of the divalent cation with the Na carrier system following Michaelis-Menten kinetics. At concentrations higher than 1 mM, the effect of Ca and Sr ions is reversed and Na and water absorption decreases slowly as Ca or Sr concentration is increased. This falling phase is ascribed to a non-specific Ca effect which produces a general "stiffening" of the membrane.
Ionic Current Measurements in the Squid Giant Axon Membrane
Authors: Cole Kenneth S. , Moore John W. 
Published: May 2004

The concepts, experiments, and interpretations of ionic current measurements after a step change of the squid axon membrane potential require the potential to be constant for the duration and the membrane area measured. An experimental approach to this ideal has been developed. Electrometer, operational, and control amplifiers produce the step potential between internal micropipette and external potential electrodes within 40 microseconds and a few millivolts. With an internal current electrode effective resistance of 2 ohm cm.2, the membrane potential and current may be constant within a few millivolts and 10 per cent out to near the electrode ends.
The maximum membrane current patterns of the best axons are several times larger but of the type described by Cole and analyzed by Hodgkin and Huxley when the change of potential is adequately controlled. The occasional obvious distortions are attributed to the marginal adequacy of potential control to be expected from the characteristics of the current electrodes and the axon.
Improvements are expected only to increase stability and accuracy. No reason has been found either to question the qualitative characteristics of the early measurements or to so discredit the analyses made of them.
Studies on the Hemolytic Properties of Protamine
Authors: Becker Frederick F. 
Published: May 2004

The basic protein protamine causes a rapid hemolysis when incubated with the red blood cells of many mammalian species. The age of the cells does not affect the process. Neutralization of the active side groups of the protamine molecule with formalinization demonstrates that a specific degree of charge is necessary for hemolysis, as more than 30 per cent of the guanidine groups must remain unreacted to maintain activity. Unlike the hemolysis induced by the synthetic polypeptides polylysine and polyhomoarginine, protamine hemolysis is temperature-dependent.
Whole lipoprotein material derived from red blood cell membranes inhibits protamine hemolysis to a greater extent than do the membranes themselves, serum, serum protein fractions, or cholesterol. The phosphatide and protein moieties derived from the membranes are quite avid in inhibiting protamine hemolysis. A probable explanation is that intracellular aggregation of these structural elements may cause changes in electrostatic charge and surface tension which result in increased permeability.
The hemolytic and antitumor cell properties of protamine could not be segregated from its animal toxicity. Despite formalinization to a degree which eliminated the former, the compound remained quite toxic to mice and rabbits.
The Secretion of Oxygen into the Swim-bladder of Fish
Authors: Wittenberg Jonathan B. 
Published: May 2004

Fish were maintained in sea water equilibrated with a gas mixture containing a non-equilibrium mixture of the three molecular species of oxygen, O18-O18 (mass 36), O18-O16 (mass 34), and O16-O16 (mass 32). Analyses in the mass spectrometer, of the gases secreted into the swim-bladder showed that no change in the relative abundance of these three molecular species had occurred during the secretory process and that therefore no exchange of atoms between oxygen molecules had occurred. Scission of the oxygen-oxygen bond probably does not occur during the transport process.
It is concluded that the active transport of oxygen into the swim-bladder by the gas gland is a transport of molecular oxygen.