Production and properties of cellobiases from immobilized cultures of aspergillus terreus R-4

ABSTRACT

Cultures of Aspergillus terreus R-4 were immobilized using different supports. The highest cellobiase activity [22.4 U/mg protein] was obtained in alginate entrapped cultures. Optimum alginate concentration and size of bead inoculum were 3% and 10 ml beads/50 ml culture, respectively. Addition of wheat bran or corn steep liquor stimulated the biosynthesis of the enzyme. Alginate beads retained 64% of their activity after 4 reuses. Purification of cellobiase [s] from free [FMC] and immobilized [IMC] cultures was fulfilled by ammonium sulphate precipitation followed by gel filtration on Sephadex G-150 and ion exchange chromatography on CM-Sephadex C50. Two cellobiases were obtained CB[im] II[b][MW 54.3-FD] from immobilized cultures and CB[f]Ia [MW 72.1 KD] from free cultures. CB[imII][b]and CB[fIa]showed optimum temperature of 65 and 60°C and optimum pH values of 5.2 and 4.8, r-espectively. CB[im] II[b]was more thermostable than CB[f]Ia and both enzymes differed in their amino acid composition. Ca[2], Ba[2+], Na[+]and K[+]ions slightly activated or stabilized both cellobiases. CB[im] I[b]was highly activated by Mn[+]2 and strongly inhibited by Hg[2+]and pdraehioromercuribenzoate, while CBI, was only partially inhibited parachloromercurilbenzoate