Summary: 148 secreted a single acid protease when cultured at acidic pH. In unbuffered medium, the culture pH eventually became alkaline and a single alkaline protease was produced. This was the only proteolytic enzyme produced when the organism was grown in buffered medium at alkaline pH. Both proteolytic enzymes were purified to homogeneity (as assessed by SDS-PAGE). The of the acid protease was 30900, the isoelectric point 4·5; optimum activity against haemoglobin was at 42 °C and pH 3·3. This enzyme was inactivated at temperatures above 46 °C and was inhibited by pepstatin and diazoacetyl-norleucine methyl ester but was insensitive to inhibition by either 1,2-epoxy-3-(-nitrophenoxy)-propane or compounds known to inhibit serine, thiol or metallo proteases. The acid protease contained 11% carbohydrate. The alkaline protease had an of 23400 and an isoelectric point of 5·4. The activity of this enzyme using azocoll as substrate was optimal at 40°C in the range pH 8·0-9·0. This enzyme was inactivated at temperatures above 42°C and was inhibited by phenylmethyl-sulphonyl fluoride and irreversibly inactivated by EDTA. The enzyme was also partially inhibited by DTT but was insensitive to either pepstatin or -chloromercuribenzoic acid.


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