To determine the role of the C-terminal region of Cellvibrio gilvus beta-glucosidase, a deletion mutant was constructed lacking five amino acid residues (RGRAR), three of which were arginine, from the C-terminal end. The mutant, designated Delta RGRAR, could be folded into an active form when expressed with the molecular chaperons GroEL/ES. In comparison with the native enzyme, the optimum pH of the mutant Delta RGRAR shifted to the acidic region and the pH stability to the neutral region, while its heat stability decreased. No significant difference in the kinetic parameter K-m was observed. It was concluded that the RGRAR residues located at the C-terminal end are quite important for the stability of the enzyme and protein folding.