Seston sedimentation

SUMMARY. Three experiments are described in which the rates of loss from suspension of Lycopodium spores introduced at the water surface in a large butyl rubber enclosure ('Lund Tube') were monitored. Rates of arrival at the mud surface and in sediment traps placed in the water column were also measured. Results obtained by each method are compared with the predetermined intrinsic sinking behaviour of the individual particles. The experiments, which were carried out under differing conditions of water-column stability (isothermal mixing, thermal microstratification, and autumnal destratification), demonstrate the importance of turbulent mixing in determining the effective settling rate of seston. A simple predictive model is developed to relate sinkinglosses to the vertical extent of broadly defined water layers. Recoveries in sediment traps can give an accurate synopsis of net sedimentation when they are operated in non-turbulent water layers, but trap performance in turbulent flow is significantly modified by hydrodynamic perturbation generated by the traps themselves.     

Convection-free boundary sedimentation

A simple technique is described that prevents the occurrence of convective flows in boundary sedimentation experiments. Superimposed density gradients employed as in band centrifugation are evaluated quantitatively. The usefulness of the method is demonstrated by comparison of stabilized and nonstabilized experiments run under identical conditions, with considerable variations in temperature introduced on purpose. The technique is shown to be of special value for the investigation of polydispersity problems.     

The evaluation of standard sedimentation coefficient in band sedimentation of macromolecules

Standardization in the calculation of the sedimentation coefficient of macromolecules by means of band techniques is discussed. When a sample of macromolecules suspended in a solvent is layered on to a denser bulk solution, the macromolecules do not sediment in this solution alone, but sediment in a mixture of bulk solution and sample solvent. This is caused by the diffusion between sample solvent and bulk solution. Experimental evidence of this process is shown during band sedimentation of ribosomes when the variation of the density and the viscosity along the cell is measured. The calculation shows that in the experimental conditions frequently used, standardization made in the usual way leads to a sedimentation coefficient which is largely overestimated; while standardization yields the correct coefficient if the diffusion effect of the sample solvent in to the bulk solution is taken into account, together with possible deuteration effects. A method to calculate the standard coefficient with the aid of a computer is proposed.     

Active enzyme sedimentation, sedimentation velocity, and sedimentation equilibrium studies of succinyl-CoA synthetases of porcine heart and Escherichia coli

Succinyl-CoA synthetases from Escherichia coli and porcine heart muscle have been viewed as prototypes of two classes of the enzyme. The bacterial enzyme has been reported to be an alpha 2 beta 2 tetramer, with many suggestions in the literature for cooperative interactions between active sites that may contribute to its catalytic efficacy. In contrast, gel filtration experiments of others have indicated that the heart enzyme is a simple alpha beta dimer, with no evidence of dimerization or interaction between like sites. All previous estimates of molecular size of these enzymes have been carried out at concentrations that are much higher than those that are used during activity measurements. The present study was carried out to confirm the differences in the quaternary structures of these two species of succinyl-CoA synthetase and to extend our knowledge of these structures to very low concentrations to enable correlation of their subunit structures with their catalytic properties. Conventional sedimentation velocity centrifugation with both enzymes indicates behavior typical of noninteracting globular proteins with no evidence of size heterogeneity. The sedimentation coefficients at infinite dilution (s20,w) have been determined to be 7.04 S and 4.55 S for the E. coli and porcine heart enzymes, respectively. Sedimentation velocity measurements have been extended to very low enzyme concentrations (typical of those used in activity measurements) by active enzyme centrifugation experiments, in which we have determined the rate of sedimentation of a zone of active enzyme through a chromogenic substrate solution.(ABSTRACT TRUNCATED AT 250 WORDS)     

Improved activity sedimentation method

The activity sedimentation method of Cohen is improved by use of a sucrose gradient to stabilize the sedimenting band. Approximate means of analyzing the data are outlined consistent with the limitations of the method. The molecular weight of a newly discovered glutamic dehydrogenase from Mycoplasma laidlawii is also estimated to be 250,000 ± 10%.     

Continuous monitoring of erythrocyte sedimentation process: a new possible mechanism of erythrocyte sedimentation

An automated system is constructed to record the complete course of erythrocyte sedimentation process. In this system a light source and a paired photodetector are employed to monitor the change of light transmittance at the junction of plasma and the sedimenting red blood cell column, thus providing a continuous record of erythrocyte sedimentation as a function of time. Differentiation of this sedimentation--time curve yields a velocity--time curve of erythrocyte sedimentation. Frequently recorded "spikes" on top of the velocity--time curve imply the episodes of very rapid fall of erythrocytes in the sedimentation tube that cannot be explained by the currently accepted theory of erythrocyte sedimentation based mainly on Stokes' law, and a new mechanism of rouleau coalescing and fracturing is proposed to account for them.     

Analyses of sedimentation equilibrium data

A numerical procedure is presented which can quite adequately compute the molecular weight averages as a function of solute concentration from sedimentation equilibrium data for homogeneous systems and for monomer-dimer associating systems with a possible extension to heterogeneous systems where monotonic variation in the weight average molecular weight is observed such as in weakly associating or dissociating systems. The procedure utilizes the method of orthogonal polynomials for curve fitting which allows for a rapid determination of best fit with minimal round off error. The procedure is particularly applicable in cases where the concentration of solute at the meniscus can be considered to be neither appreciable and reasonably well determined as in low speed sedimentation equilibrium experiments, nor essentially zero as in high speed sedimentation equilibrium experiments where the calculations become somewhat more simplified. The use of moderate speed sedimentation equilibrium has the advantage of providing a more broad concentration distribution in the centrifuge cell which yields more extensive information concerning dissociating systems yet still provides results at low solute concentrations where most solutes can be considered to be behaving ideally.     

Cell sedimentation with gravity activation

Murine monoclonal antibody T101 has been coupled to thinly polymer-coated heavy alloy particles (LaMn2Ge2). These conjugates are coupled to cultured cells of the human T-cell leukemia line RPMI 8402 (T8402). The sedimentation velocities of cells, of particles, and of cells with particles attached are measured. After determining the mean radii of cells, of particles, and of cells with particles attached, one may compute a mean number of 33 particles attached to a cell. Independently one may compute a mean number of 144 particles/cell for surface saturation. The Appendix handles the underlying theory in three parts: number of particles/cell, saturation number of particles/cell, and resolution for gravity activation. Regarding the latter, cell radii from 4 to 10 microns and particle radii from 0.01 to 1 micron are considered.     

The differentiated erythrocyte sedimentation rate

Summary The author has studied Erythrocyte Sedimentation Rates in the open air and in a copper container. All blood samples were obtained, every time, from the same subject. The results of the experiments, which lasted from May to September 1957, show a significant effect of the copper shield. The present article is the continuation of the studies published by the author in the Int. Journ. of Biocl. and Biomet. vol I, part IV, section C 1, 1957.     

Anomalies in sedimentation. IV. Decrease in sedimentation coefficients of chains at high fields

A theory is presented for the decrease of sedimentation coefficient at high centrifugal fields recently reported for samples of DNA by Rubenstein and Leighton and others. The theory uses the model of a chain of beads and springs to represent the molecule. Kirkwood's approximation is used for the sedimentation coefficient. The decrease in sedimentation coefficient with field comes about as a result of the uneven frictional forces in the chain, which on the average are less on segments near the center of the chain than on those near the ends. As a result the ends of the chain tend to drag behind the center, and the average intersegment distances are increased; consequently the hydrodynamic shielding of one segment by another is reduced, and the average friction is increased. The effect is thus characteristic of single molecules; intermolecular interaction is not involved. The sedimentation coefficient, S, varies as a power series in a parameter y that measures the distortion produced by the uneven friction: S = S⁰(1?D₂y² + D₄y⁴ ? ·). where S⁰ is the limiting value of S at zero centrifugal field and D₂ and D₄ are constants; y is proportional to the cen speed squared tunes the molecular weight squared divided by S⁰. It has been observed that the effects of centrifuge speed on S are negligible below certain critical values of the speed and molecular weight, but increase dramatically immediately above these values; this follows naturally from the high powers of the speed and molecular weight that appear in the above equation.