Š. Štokrová

Conformational study of poly(α,β-L-aspartic acid)

The conformation of poly(α‐L‐aspartic acid) was investigated on a sample in which β‐bonds were not detected. CD and ir spectroscopy showed that poly(α‐L‐aspartic acid) passes through a conformational change induced by changes of the degree of ionization that is accompanied by precipitation; the precipitate is probably highly helical. The change was also detected by potentiometric titration.

Characterization of Seed Globulins from Three Cucurbita Species: Effect of pH on the Dissociation and Circular Dichroism Spectra

Summary The effect of pH on the sedimentation behaviour and circular dichroism spectra of seed globulins isolated from three Cucurbita species (C. maxima, C. pepo and C. moschata) was investigated. Four clearly defined seed globulin components were recognized by the ultra centrifugation under given experimental conditions. The component with values of approx. 12S dominated over 7 S and 18S ones in the NaCl-solutions with pH-values of 5.85, 8.4, 9.35 and 9.75, respectively. The fast sedimented fraction (18 S) was present only in a negligible amount. The occurrence of 7 S component was typical mainly for the region of pH values between 10.2 and 11. The existence of 3 S species was proved only in the strong alkaline region (pH ≥ 11). The molecular weight of the 3.3 S component determined in the case of Cucurbita maxima was 53,000 daltons. There is a little difference between the CD spectra of various Cucurbita species at neutral pH. Following the changes of globulin conformation as a function of pH of the solution it was observed that with increasing pH the relative amount of the unordered form increases at the expense of a-helix and the sum of relative concentrations of β-form and β-turn.

NATURE OF PROTEIN – DNA INTERACTIONS REVEALED BY MODEL POLYPEPTIDE COMPLEXES

Publisher Summary Generally, two types of DNA - binding proteins can be recognized: (1) specific binding proteins, for example, repressors and other regulatory proteins and (2) nonspecific binding proteins, for example, histones or protamines. The primary and higher structures of the entire protein molecule may affect the binding to DNA. It is assumed that the binding is largely determined by the structure of the binding polypeptide segment. Basic polypeptides are designed and synthesized with controlled amino acid composition and sequence to study the effect of polypeptide primary structure and conformation on the binding to DNA. The affinity of polypeptides to DNA and the mechanism of binding are substantially affected by two factors in the polypeptide primary structure: the nature, content, and distribution of basic residues and, the presence of strongly hydrophobic residues.