Production of Thermophilic Extracellular Proteases (Aqualysins I and II) by Thermus aquaticus YT-1, an Extreme Thermophile

Abstract

The progress of growth of Thermus aquaticus YT-1 and production of casein hydrolytic enzyme in the culture supernatant were followed, and it was found that the cells produced at least two kinds of extracellular proteases. The properties of the crude enzymes were examined. One of the extracellular proteases, which we call aqualysin I, is an alkaline protease which was secreted linearly from the early stationary phase until the time the cells ceased to grow. The optimum temperature of the proteolytic activity was between 70 and 80°C, and the enzyme activity was inhibited by diisopropyl fluorophosphate. The other which we call aqualysin II is a neutral protease, the production of which was observed remarkably from 4 days and continued linearly for 5 days. The maximum activity was obtained at 95°C (the highest temperature tested), and the proteolytic activity was inhibited by diisopropyl fluorophosphate, ethylenediaminetetraacetate and ethyleneglycol-bis (β-aminoethyl ether)-N, N'-tetraacetate.