Continuous conversion of glutamine to glutamate by immobilized glutaminase-producing yeast

Yeast cells with a salt-tolerant and thermostable glutaminase were immobilized in silica gel (S gel) and/or alginate-silica complex gel (AS gel). The inhibition rate of the conversion rate of immobilized cells by NaCl were lower than that of free cells. The glutaminases of immobilized cells and free cells were not inactivated by heat treatment at 60°C for 1 h. The half-lives of glutaminase in AS gel were 310 d at 40°C, 40 d at 45°C, and 14 d at 50°C at a constant space velocity (SV) of 0.64. The half-life of the glutaminase activity in cells immobilized in AS gel was longer than that in S gel. By passing a filtrate of wheat gluten hydrolyzed by proteolytic enzymes through the column containing the cells immobilized in AS gel at SV of 0.20, 10 mg/ml of glutamate was continuously produced.