Studies on the extracellular p-nitrophenyl ?-d-cellobiosidase activity of a thermophilic streptomycete

Abstract

The activity of ten actinomycete strains against p-nitrophenyl fl-D-cellobioside (pNPC) was investigated. Intra-and extracellular activities were detected in all strains, although activities were found to vary between strains. Extracellular pNPC activity, detected in the thermophilic Streptomycete EC22 was six times greater than that of the next best strain. Culture supernatant studies on Streptomyces strain EC22 revealed that pNPC activity was optimal at 65 ° C and between pH 6.0 and pH 8.0, although this temperature value represented a compromise between increased reaction rate and thermal denaturation. At 65°C, the half-life of activity against pNPC was 150 min. The Km value of pNPC activity was found to be 3.33 mM. Enzyme activity was subject to competitive inhibition by both glucose and cellobiose with substrate inhibition constant (Ki) values of 2.2 mM and 1.4 mM respectively. Fast protein liquid chromatograph (FPLC) of culture supernatants from EC22 using anion exchange chromatography revealed the presence of two proteins with pNPC activity. This result was confirmed using gel-filtration chromatography which estimated the molecular mass of the two proteins to be approximately 48 and 33 kDa, with the specific activity of the 48 kDa enzyme being eight times greater than that of the 33 kDa protein.

Microorganisms in the Conversion of Agricultural Wastes to Compost

“…Under appropriate conditions bacteria degrade cellulose and hence many bacterial strains are known to solubilize and modify the lignocellulosic structures extensively. But their ability to mineralize lignin is limited [18]. Cytophaga.…”