Production and Characterization of a Crude Thermostable Invertase from Cryptococcus laurentii S23

Abstract

A yeast strain isolated from soil and identified as Cryptococcus laurentii was found capable of producing thermostable extracellular invertase. The extracellular enzyme was thermostable, and the optimum temperature, pH and time for enzyme-substrate reaction were found to be 60°C, 5.5 and 5 min, respectively. Mn2+ stimulated the activity of enzyme significantly while Co2+, Ca2+, Cu2+ and Fe3+ showed little stimulatory effects. Cetyltrimethylammonium bromide showed stimulatory and ethylenediaminetetraacetic acid showed inhibitory effects on enzyme activity. Enzyme was found to be thermostable up to 60°C at pH 5.5. The maximum invertase production (35.32 IU ml−1) was achieved at 30°C, 120 rpm and pH 4.5 on 48 h using 1.0% cell suspension (24 h old) as inoculum in 50 ml medium in 250 ml Erlenmeyer flask. The superior carbon and nitrogen sources for the production of invertase were found to be sucrose (2.0%), peptone (nitrogen level 1 mg/ml). The Km and Vmax were 2.9 mg ml−1 and 39.7 mg min−1 ml−1, respectively. The maximum enzyme activity obtained was 44.72.