Poultry feathers make up for as much as 8.5% of chicken weight and represent a considerable amount of almost pure keratin waste which is not being adequately utilized at the present time. The present study dealt with the processing of poultry feathers through a two-stage alkaline-enzymatic hydrolysis. In the first stage, feathers were mixed with a 0.1 or 0.3% KOH water solution in a 1 : 50 ratio and were incubated at 70°C for 24 h. After adjusting pH to 9, the effects examined in the second processing stage on the amount of degraded feathers were those of proteolytic enzyme additions (1-5%), time (4-8 h) and temperature (50-70°C). Processing feathers in 0.3% KOH and hydrolysing for 8 h in the second stage at 70°C with a 5% dose of enzyme (relative to dry feathers weight) produced approx. 91% degradation. Keratin hydrolysate is distinct for its high nitrogen content and reasonable inorganic solids level. Two-stage technology of alkaline-enzymatic hydrolysing of poultry feathers in an environment of 0.3% KOH achieves high efficiency under quite mild reaction conditions (temperature not exceeding 70°C with pH in a mildly alkaline region), and is feasible from an economic viewpoint. Keratin hydrolysate can find particular application in packaging technology (films, foils and encapsulates).

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Hyaluronic acid (hyaluronan, HA) is a negatively charged polysaccharide forming highly swollen random coils in aqueous solutions. Their size decreases along with growing salt concentration, but the mechanism of this phenomenon remains unclear. We carry out molecular-dynamics simulations of a 48-monosaccharide HA oligomer in varying salt concentration and temperature. They identify the interaction points of Na + ions with the HA chain and reveal their influence on the HA solvation-shell structure. The salt-dependent variation of the molecular size does not consist in the distribution of the dihedral angles of the glycosidic connections but is driven by the random flips of individual dihedral angles, which cause the formation of temporary hairpin-like structures effectively shortening the chain. They are induced by the frequency of cation-chain interactions that grow with the salt concentration, but is reduced by the simultaneous decrease of ions' activities. This leads to an anomalous random-coil shrinkage at 0.6 M salt concentration.

A computational method of modeling random coils of hyaluronan was developed based on the molecular-dynamics simulations. An oligosaccharide of 48 monosaccharide units was equilibrated within a 70-100ns simulation and randomly chosen pieces of this molecule from different simulation frames were combined to constitute a long polysaccharide chain, both for hyaluronan and its non-ionic analog containing glucose instead of glucuronic acid. The dihedral angles of the glycoside connections of the pieces obeyed the statistics deduced from the simulation. The simulations were performed at various concentrations of NaCl and MgCl. The calculated radii of gyration show a striking agreement with experimental data from the literature and indicate a key importance of the polymer-ion interactions for the random-coil conformation, but a low influence of the excluded volume of the chain and the carboxylate-groups repulsion. The method has thus the potential to become a versatile tool of modeling macromolecules of various semirigid polymers.

High-pressure methods have become an interesting tool of investigation of structural stability of proteins. They are used to study protein unfolding, but dissociation of oligomeric proteins can be addressed this way, too. HIV-1 protease, although an interesting object of biophysical experiments, has not been studied at high pressure yet. In this study HIV-1 protease is investigated by high pressure (up to 600 MPa) fluorescence spectroscopy of either the inherent tryptophan residues or external 8-anilino-1-naphtalenesulfonic acid at 25°C. A fast concentration-dependent structural transition is detected that corresponds to the dimer-monomer equilibrium. This transition is followed by a slow concentration independent transition that can be assigned to the monomer unfolding. In the presence of a tight-binding inhibitor none of these transitions are observed, which confirms the stabilizing effect of inhibitor. High-pressure enzyme kinetics (up to 350 MPa) also reveals the stabilizing effect of substrate. Unfolding of the protease can thus proceed only from the monomeric state after dimer dissociation and is unfavourable at atmospheric pressure. Dimer-destabilizing effect of high pressure is caused by negative volume change of dimer dissociation of −32.5 mL/mol. It helps us to determine the atmospheric pressure dimerization constant of 0.92 μM. High-pressure methods thus enable the investigation of structural phenomena that are difficult or impossible to measure at atmospheric pressure.