Purification and characterization of the heat-stable serine proteinase from Thermomonospora fusca YX

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Abstract
The proteinase secreted from Thermomonospora fusca YX grown on cellulose was purified by (NH4)2SO4 fractionation and cation-exchange chromatography. The isolated proteinase readily hydrolysed several proteins and demonstrated activity towards casein from 35 to 95.degree. C (at pH 8.0) with maximum activity at 80.degree. C. It exhibited broad pH and ionic-strength optima centered at pH 9.0 and 0.2 M-NaCl respectively, and it retained high activity in the presence of 2% (w/v) SDS, 20 mM-dithiothreitol and 1.0 M-NaCl. The proteinase, which was fully inhibited by phenylmethanesulphonyl fluoride, had an Mr of 14500 and an isoelectric point at 9.21. A measurement of proteinase thermal stability demonstrated a T50% (15 min) of 85.degree. C at pH 4.5.