Abstract
An extracellular protease in Isaria cicadae extracted from a liquid culture with wheat bran was purified and characterized. This mushroom showed two morphologies on agar plates: mycelia with and without conidia. High enzyme activity was detected in the culture filtrate extract of the mycelia with conidia. The enzyme was purified 13-fold with a yield of 33% using CM-Sepharose column chromatography. Electrophoretic analysis of the purified enzyme showed a single band. The molecular mass of the enzyme was 30.6 kDa by SDS-PAGE and 31 kDa by gel filtration. The N-terminal amino acid sequence of the protease was AFTTQPGAVW. The optimum temperature and pH were 55℃ and 9.0, respectively. The enzyme was stable in the pH range 4 to 7. The Km value for the hydrolysis of casein was 0.48mg/mL. The enzyme activity was strongly inhibited by phenylmethylsulfonyl fluoride. From the results, it is suggested that the enzyme is a serine protease.
