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DISSYMMETRIES LIGHT SCATTERING OF BIOPOLYMERS
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PHOENIX INSTRUMENTS FOR MOLECULAR WEIGHT £ SIZE STUDIES
Looking for a suitable topic for this column, we flipped through the subject index for the year 1966 (Vol. 5) of "Biochemistry," monthly journal published by the American Chemical Society. Under Light scattering, there were six papers mentioned, the authors, titles, and references of which were as follows : (a) M . D. Stern (p. 2558), On the Estimation of Molecular Dimensions and Shape of Rigid, Asymmetric Macromolecules from Hydrodynamic Measurements. (b) K. Barterjee and M . A. Lauffer (p. 1957), Polymerization— Depolymerization of Tobacco Mosaic Virus Protein. VI. Osmotic Pressure Studies of Early Stages of Polymerization. (c) H. T. Miller and R. E. Fecney (p. 952), The Physical and Chemical Properties of a n Immunological Cross-Reacting Protein from Avian Egg Whites. (d) D . B. Millar and R. F. Steiner (p. 2289), The Effect of Environment on the Structure and Helix-Coil Transition of Soluble Ribonucleic Acid. (c) P . S. Sarfare, G. Kegeles and S. J. Kwon-Rhee (p. 1389), Relationship between Active Sites and Polymerization Sites in a-Chymotrypsin.
THE N E W P H O E N I X A U T O M A T I C S C A N N I N G , L O W - A N G L E LIGHT-SCATTERING PHOTOMETER . . . designed t o yield size and shape information in the 0.2 to 200 Micron diameter range.
(f) E . Chiancone, M . S. Bruzzesi, and E . Antonini (p. 2823), Studies of Dextran and Dextran Derivatives. X. The Interaction of Dextran Sulfate with Lysozyme. The first paper listed above deals with some theoretical aspects of the evaluation of the lengths of different models for the rigid asymmetric macromolecules. A comparison has been made with the lengths derived from the radius of gyration as measured by light scattering. Such a comparison offers a possibility of distinguishing between different models. Data for paramyosin, light meromyosin, tropomyosin B, and tobacco mosaic virus were discussed. Paper (b) presents mostly the osmotic pressure results of the polymerization of the protein moiety of the tobacco mosaic virus. Some light scattering measurements by means of the transmittance technique were also made and compared with the osmotic pressure data.
THE BRICE-PHOENIX LIGHT-SCATTERING-PHOTOMETER . . . measures molecular and micellar weights f r o m 300 t o I Billion. Also measures size, shape, mass . . . interactions in solutions, turbidity, dissymmetry and depolarization.
The other four papers describe, among other information, the results of light scattering investigations, in all of which BricePhoenix light scattering photometers were used. In addition to the usual molecular weight determination, the interactions of biopolymers and small ions and molecules, as well as the interaction of biopolymers with other biopolymers were explored by means of light scattering. Miller and Feeney (c) of the Department of F o o d Science and Technology, University of Davis, California, found for the molecular weight of an immunologically cross-reacting macroglobulin in chicken egg white a value of approximately 8 Χ 105, in agreement with the value obtained from sedimentation-diffusion. The influence of magnesium ion, neutral salt, and ribonucleotide concentration on the molecular weight of soluble ribonucleic acid (s-RNA) was studied in paper (d) by Millar and Steiner at the Naval Medical Research Institute, Bethesda, M d . s-RNA exhibits a polyelectrolyte behavior as evidenced by the effect of the ionic strength of the medium o n the apparent molecular weight. A molecular weight (at infinite dilution) of about 23,000 to 25,000 is indicated. Magnesium ions cause a n increase of the apparent molecular weight: s-RNA exists largely in associated form in 0.02 M M g + + at concentrations greater than 2 m g . / m l . and at 25 °C.
THE BRICE-PHOENIX DIFFERENTIAL REFRACTOMETER . . . measures the difference in refractive index between solutions and its solvents and concentrations . . . has greater accuracy, extended range and increased stability, with sensitivities to I 0 " 6 R. I. units. These instruments are baclted-up by over 1000 published bibliographies compiled since 1945 on light-scattering, covering 22 categories from aerosols to synthetic polymers. Send for FREE LITERATURE KIT containing these valuable references, as well as reprints and bulletings on light scattering instrumentation.
PHOENIX PRECISION INSTRUMENT COMPANY World WideSales&Service A Subsidiary of IÇβflCÔ] INSTRUMENTS CORP. 3 8 0 3 - 0 5 N. 5th Street. Philc, Pernio. 19140 U.S.A.
Sarfare et al. (e) at Clark University, Worcester, Mass., investi gated whether polymerization of α-chymotrypsin takes place via the active sites of the enzyme monomer units. To this effect, the dependence of the weight-average molecular weight was studied as a function of enzyme concentration in the presence of various amounts of /3-phenylpropionate, a competitive inhibitor. The re sults have been compared with the predicted molecular weights computed for several models involving the existence of various distinct polymeric species. I t was confirmed that the active sites were accessible regardless of the polymerization of the enzyme. Finally, the interaction between two biopolymers were studied in paper (f) at the University of R o m e . Since lysozyme carries a net positive charge a t neutral p H and dextran sulfate is negatively charged, a strong interaction between the two was expected on elec trostatic grounds. Depending on the conditions, both soluble and insoluble (precipitated) macromolecular complexes were formed. The tendency to precipitate increases at low ionic strength, p H and temperature. A quantitative evaluation of the results obtained for soluble complexes has been attempted on the basis of models in volving a reversible association-dissociation equilibrium and different stoichiometric ratios. If you would like reprints of the previous articles in this series as well as complete information on the instrumentation described in the above study, write Phoenix Precision Instrument Co., 3803 N . 5th Street, Phila., Penna. 19140. © Copyright 1968
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