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In order to determine the intermolecular forces in the process of the heat aggregation of globular proteins in solution, selected proteins with different amounts of disulfide- and thiolgroups were investigated by specific inhibition experiments and by degradation analysis, using lightscattering and ultracentrifugation methods.
In accordance with the mechanism of the heat aggregation, which in general (SH —SS-proteins) may be characterized as a coupled coagulation- and exchange-reaction, auxiliary valences and covalent bonds take part in the aggregation process.
Besides the pʜ-range of lanthionine-formation, the coagulation-mechanism by weak intermolecular forces exceeds the covalent type of aggregation.
If only one of the sulphur functional groups is present in the protein molecules the aggregation is merely the result of the coagulation-mechanism, i. e. the degradation by urea, guanidine·HCl, variation of pʜ etc. leads back to the monomer.
In the case of SH —SS-proteins the degradation rate depends on the temperature and duration of aggregation: In the range of predenaturation and under isoelectric conditions the native monomer is restored while increasing net charge leads more and more to covalently bound aggregates which are due to disulfide- and lanthionine-groups. High alkalinity promotes the formation of lanthionine.
Regarding the weak intermolecular bonds the application of specific criteria in degradation and inhibition experiments proves that Η-bonds and hydrophobic interactions participate in the aggregation process while ion pair bonds may be excluded. The hydrophobic interactions do not become apparent, until partial denaturation of the aggregating protein takes place.
The proportion of the total aggregation at extreme pʜ-values which is produced by the coagulation mechanism may be explained in a tentative way by assuming specific electrostatic short range interactions between the partially dehydrated molecules, leading to fibrillar associates.
Steroid initiated enzyme induction (Δ5-Ketosteroid-Isomerase, 3α-Hydroxysteroid-Dehydrogenase, and 3β.17β-Hydroxysteroid-Dehydrogenase) in Pseudomonas testosteroni was investigated with respect to the kinetics of induction, operon control of the induced enzymes, and the relative strengths of various inducers. The induction process was followed indirectly by selective inhibition of different stages in the protein synthetic pathway. Comparisons between bacterial and mammalian steroid induction are discussed.
Glycol causes a denaturation of the DNA double helix structure in solution. As could be shown earlier, heat denaturation of DNA leads to an increased dimerization of thymine following uvirradiation. In contrast to this, thymine dimer is not increased - but is even slightly decreased - when DNA is uv-irradiated in the presence of glycol. These results are discussed with regard to the distortion of the hydration layer and the hydrophobic stacking of bases, as influenced by glycol.
Investigations were made of energy-transfer in liquid scintillators under UV- and β-excitation. The influences of n-hexane and methanol as diluting solvents on the scintillation process in p- terphenyl-toluene were measured. Differences of energy transfer under β - and UV-irradiation are discussed. Radiationless energy-transfer occurs over distances from 15 to 32 Angström units. Quenching effects of phenol on p-terphenyl, 2,5-diphenyl-oxazole, and 2,4 (or 5) -diphenyl-imidazole were studied. Oxygen-quenching in liquid scintillators containing hydroxy-benzenes was investigated. The results are in correspondence with the KALLMANN-mechanism of radiationless energy-transfer. — Further investigations were made of the connection between the chemical structure of aryl-imidazoles and their scintillation properties. Scintillation properties depend on spectral data. The results aprove HELLERS postulates, concerning structural requirements for good scintillation properties of organic liquid scintillators.