A. R. Peacocke

Thymus deoxyribonucleoprotein III. Sedimentation behaviour

Abstract The sedimentation behaviour of soluble thymus deoxyribonucleoprotein in different concentrations of salt has been examined by using ultraviolet-absorption methods. The sedimentation coefficients of fresh solutions of different preparations of deoxyribonucleoprotein in dilute phosphate buffer were reproducible to within 10% and extrapolated to 32 S at infinite dilution. This value, in combination with light-scattering and viscosity measurements, confirmed that deoxyribonucleoprotein in this solvent consists of discrete molecules with the configuration of a moderately stiff coil. The shape of the sedimenting boundary remained constant in different concentrations of salt, in spite of dissociation. It was concluded that within any one molecule of deoxyribonucleoprotein there is a range of stability of binding of the histone protein to the DNA. Analysis of supernatant fractions showed that histones of relatively smaller arginine and greater lysine content were bound least strongly.

The physical properties of a glycoprotein from bovine cortical bone (bone sialoprotein)

Physicochemical studies have been made of two different preparations of bone sialoprotein, a glycoprotein from bovine cortical bone, which contains a high proportion of sialic acid groups. Determinations have been made of s020,w, diffusion coefficient, molecular weight, sedimentation coefficient distribution, optical rotatory dispersion curves, mobility during free boundary electrophoresis, partial specific volume and refractive index increment. The two preparations differed slightly in molecular weight, but both are small molecules, polydisperse but homogeneous with respect to centrifugation and electrophoresis. Their frictional coefficients are higher than that expected for globular molecules and they have little or no helical content. The results are discussed in the light of available analytical and structural information.

The ultraviolet absorption of some degraded desoxyribonucleic acids.

Abstract Measurements have been made of the atomic extinction coefficient with respect to phosphorus, at 259 mμ of various samples of degrade DNA. The nucleic acids used were isolated from animal, plant and microbial sources and were degraded by acid and alkali, ultrasonic waves, an enzyme, and by heat treatment. The thesis is developed that treatment which results in a decrease in intermolecular forces does not affect the absorption spectrum, whereas scission of intramolecular hydrogen bonds results in an increase in the optical density of the DNA solution.

Thymus deoxyribonucleoprotein I. Preparation and thermal denaturation

Abstract Preparations of undissociated deoxyribonucleoprotein having a reproducible composition were obtained from calf-thymus glands essentially by extraction with water. Spectrophotometric titration and other ultraviolet-absorption measurements showed that this deoxyribonucleoprotein was denatured by heat and by alkali in both 0.001 M and 1.0 M sodium chloride in a manner similar to DNA. This similarity confirms that the double-helical structure of DNA exists within the original undissociated deoxyribonucleoprotein complex in solutions.

The binding of hydrogen and calcium ions by Tamm-Horsfall glycoprotein

Abstract 1. 1. The hydrogen ion titration curves of Tamm-Horsfall urinary glycoprotein in 6 M guanidine · HCl showed that, for every 100 000 g unit, the 16 sialic acid residues revealed by analysis were fully titratable, but only 92 residues of aspartate, glutamate and α-carboxyl groups out of a total of 128 were available to react with H + . 2. 2. The titration curve of this glycoprotein from fibrocystic children was similar. 3. 3. An ultrafiltration technique has been developed to measure Ca 2+ binding directly in the range of Ca 2+ concentration (0.5–9 mM) over which marked increases in viscosity have been observed. 4. 4. Ca 2+ binding at first increased approx. linearly with concentration of free Ca 2+ and revealed a maximum of 0.45 mmole Ca 2+ /g glycoprotein bound at 6 mM of free Ca 2+ , when gel formation occurred. 5. 5. The maximum binding of Ca 2+ corresponds to an approx. 80% neutralisation of the total negative charge determined by titration. 6. 6. The implications of these findings are discussed in relation to the possible physiological relationships between Ca 2+ and the urinary glycoprotein.

Studies on a complex of deoxyribonucleic acid with non-histone protein

Abstract A complex of deoxyribonucleic acid and protein has been isolated from rat liver according to the procedure of Kirby and Frearson . This complex contains a small amount (2 %) of firmly bound protein which was shown not to be histone by amino acid analysis. Unlike rat-liver deoxyribonucleic acid, the sedimentation behaviour at concentrations above 0.04 mg/ml indicated the presence of aggregates. Sodium 4-aminosalicylate, and 2 M NaCl (used either conjointly or consecutively) and 4 M urea have been found to dissociate these aggregates, as judged from the change in sedimentation distribution curves. From these observations the role of various types of bonding (metal chelation, electrostatic, hydrophobic and hydrogen bonding) within the complex and in its aggregates has been inferred.

The isolation, composition and physicochemical properties of deoxyribonucleic acid from Bordetella pertussis

Abstract The percentage by weight of deoxyribonucleic acid in Bordetella pertussis is large. A method is described for the isolation of DNA from this bacterium in a relatively pure and undegraded form. DNA was extracted from several strains and had a base composition of 67.6% GC 2 ; in one case, however, the composition was 57.5% GC. The two types of DNA were studied further: they contained no large amounts of bases other than the usual four, their light-scattering and sedimentation properties were very similar, and their thermal denaturation properties were consistent with the difference in base composition.