A bacterial extracellular proteinase degrading silk fibroin

The bacterium Variovorax paradoxus, grown in a minimal medium in which silk fibroin represents the sole source of carbon and nitrogen, produces an extracellular protease that hydrolyzes fibroin as well as casein and, to a smaller extent, collagen and albumin. The optimal pH for activity was found to be in the acid range (optimum pH 5.8–6.4) and the enzyme activity was stimulated by the addition of divalent cations, either manganese or magnesium. Gel permeation chromatography and SDS-PAGE provided evidence that the native enzyme is a monomer with a Mr of ca. 21 kDa.