Keratinolytic activity of Kocuria rosea

A strain of Kocuria rosea able to secrete keratin-hydrolysing proteinases (keratinases) in submerged batch cultures with finely milled feathers as carbon and nitrogen sources was studied. The highest production of keratinases was obtained when feathers were used as the only fermentation substrate (17 U/mg). Considerably lower activity was present in cultures containing glucose and others nutrient supplements. The optimum temperature and pH for keratinolytic activity was 40 °C and 10, respectively. Gelatin-sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE) electrophoresis analysis showed that Kocuria rosea grown on feathers secreted at least two alkaline extracellular proteases with apparent molecular weights of 90.2 and >200 kDa, respectively. These proteolytic activities appear sequentially during microbial growth. Keratinolytic activity was strongly inhibited by phenylmethanesulphonyl fluoride (PMSF), chymostatin and crystalline soybean trypsin inhibitor, indicating the presence of serine proteases. Proteolytic enzymes derived from the biodegradation of feathers by this microorganism could be a useful biotechnological tool in the leather, food and cosmetic industries.     

Transport properties of oligomeric subunit structures

The translational friction coefficients, rotational friction coefficient, and intrinsic viscosity of rigid regular structures composed of up to eight identical spherical subunits have been accurately calculated. The aim of this calculation is to interpret the hydrodynamic properties of oligomeric subunit proteins. To avoid the well-known failure of the theory in the evaluation of rotational coefficients and intrinsic viscosities, each subunit is hydrodynamically modeled as a polyhedral array of smaller spheres. The analysis of several alternatives suggests that a cubic array is the best choice. The reliability of this strategy is checked by comparison of the calculated values for all the transport properties of a sphere and the translational friction coefficients of a dimer with their exact values. Finally, the hydrodynamic properties of a number of subunit structures with varying number of subunits and different geometries are tabulated.