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Biomedical subjects

J W Beams

Publications and source records attributed to J W Beams.

12 recordsLinked to original sources
PubMed1977

Simultaneous measurements of viscosity and density in solutions undergoing change.

The magnetic suspension densimeter-viscometer has been modified so that the variations of viscosity and density in solutions undergoing change are determined continuously as a function of time. The changes in values for both of these properties are also obtained when solutions of varying composition are passed through the sample cell (<0.5 ml). The new method measures the torque on the magnetically suspended buoy which is held stationary in a stable velocity gradient; this procedure also facilitates the measurement of the density with greater accuracy. Preliminary results relating to the conformation changes of ribonuclease A in the presence of guanidinium chloride and a disulfide cleaving agent are presented.

Journal Article↗
PubMed1977

Solid-like character of virus solutions.

The solid-like behavior of turnip yellow mosaic virus solutions following the extrusion of viral RNA in alkali was observed with a torsion-fiber balance developed for the purpose. This method provided a direct measurement of the yield stresses required to break or liquefy these solutions. The yield stresses were found to increase and to be less time dependent with increasing concentrations of the virus and they were maximal at room temperatures. If the virus had been damaged, as by freeze-thaw, little or no solid-like behavior could be demonstrated. Purified viral capsids, with or without added RNA, were also inactive. The values for the yield stresses were of the same order as the value reported previously with the use of a magnetic suspension viscometer; hence, the apparent coherency appears unrelated to the magnetic fields generated by the latter instrument. These solutions behaved as typical liquids after the required stress was applied [about 0.005 to 0.17 dyne cm-2 (0.05 to 1.7 micronN cm-2)], these forces being smaller than those usually conferred by ordinary handling.

Freezing↗
PubMed1975

Quasi-elastic behavior of solutions of viral capsid and RNA at very low shearing stresses.

By the application of shearing stresses on the order of 10(-3) dyne cm-2 (10(-2) muN cm-2), via the magnetic viscodensimeter, extremely high relative viscosities (greater than 500) were observed when turnip yellow mosaic virus was degraded in alkali into its capsid and RNA. The solutions, however, possessed a watery consistency at this stage and exhibited a quasi-elastic character by rotor-recoil experiments. The development of this curious behavior was concentration and temperature dependent; it was not seen less than 0.5% nor at 8 degrees, and appeared sooner at 30 degrees than at 20 degrees. The time of appearance was delayed as the pH was lowered; however, the effect was still observed when the pH was as low as 9. Whereas reversibility was demonstrated when the shearing stresses exceeded the elastic resistance [0.17 dyne cm-2 (1.7 muN CM-2)], thorough mixing usually resulted in a normal behavior of the solutions thereafter. Values for the modulus of rigidity at 20 degrees for about 1% virus concentration was less than 2 X 10(-2) dyne cm-2 rad-1 (0.2 muN cm-2 rad-1), which, while extremely small, was reproducible. A porous structure, possibly involving a capsid and RNA complex, is envisioned.

Mosaic Viruses↗
PubMed1974

Equilibrium sedimentation of turnip yellow mosaic virus.

Sedimentation equilibrium was achieved with turnip yellow mosaic virus at low speeds (600 rpm) in a magnetic ultracentrifuge. The experiments were carried out in the newly installed constant-speed rotor, equipped with automatic control and an electromagnetic drive. A particle mass of 5.55 x 10(6) daltons was calculated for the virus at vanishing concentrations, in essential agreement with the earlier results using the more tedious procedure with a freely coasting rotor. In order to interpret the observed departure from ideal behavior (nonassociating conditions), preferential interaction experiments were carried out by magnetic densimetry. These showed that a strong Donnan effect exists at pH 7, which contributed > 10(3) times more to the nonideality than did the excluded volume effect. A net negative charge of about 3.5 x 10(3) per particle was estimated at this pH.

Densitometry↗
PubMed1973

A magnetic suspension osmometer.

The magnetic suspension balance is used for the measurement of very small osmotic pressures. The apparatus is essentially the same as that previously used for the measurement of the density and viscosity of protein solutions except that the magnetically suspended buoy is modified to make it pressure sensitive. The method is especially useful for the measurement of osmotic pressure in small samples of dilute solutions (about 10(-6) M) or of substances with molecular weights greater than 10(5). A height-sensing device has been developed which is not dependent upon the visual precision of the operator.

Animals↗
PubMed1972

Simultaneous determination of viscosity and density of protein solutions by magnetic suspension.

The first results are reported with a magnetic suspension instrument for determination of the viscosity and density concurrently on small volumes (0.2 ml) of protein solution. Reasonable agreement was obtained with literature values for the intrinsic viscosities and specific volumes (partial or isopotential) of serum albumin and ribonuclease in native solvents, and in 6 M guanidinium chloride with or without 2-mercaptoethanol. Turnip Yellow Mosaic virus and myosin were also studied, the results with the virus being related to hydration and structure data and those with myosin to the dissociative character of the protein. The possibility of using this approach to follow the time course of viscosity and density changes during reactions is shown.

Chlorides↗
PubMed1969

Effect of pressure on the apparent specific volume of proteins.

The magnetic densimeter has been employed to measure the densities and apparent specific volumes of certain proteins in aqueous solutions as a function of pressure. The method gave values in satisfactory agreement with those found in the literature for aqueous electrolyte solutions. A change in apparent specific volume of the monomeric proteins, ribonuclease and turnip yellow mosaic virus and its capsid protein, at pressures up to 400 atmospheres at 20 degrees C was not observed within the precision of the measurements. Also, no change in the apparent specific volume of tobacco mosaic virus protein was observed as a function of these pressures whether the protein was predominantly in the polymerized or unpolymerized state. The magnetic densimeter was found to be a convenient instrument for measuring compressibilities of very small samples of solutions.

Densitometry↗