Purification and characterization of the extracellular proteinase of Serratia marcescens

The extracellular proteinase produced by a depressed strain of Serratia marcescens ATCC 25419 was purified and characterized. This produces more than 10-times the amount of extracellular proteinase produced by other strains of Serratia tested. The purified enzyme was prepared from the culture supernatant by (NH4)2SO4 fractionation and DEAE-cellulose chromatography. The purified enzyme has an so20,w of 3.95 and is a monomer of molecular weight 51,900. The proteinase has a broad pH optimum in the alkaline range with a maximum at pH 9.5. The enzyme will utilize a number of proteins as substrate. The products of digestion are primarily in the size range of tripeptides to hexapeptides. Peptides containing a sensitive bond and a minimum size of size amino acids are hydrolyzed. The proteinase is inhibited by chelating agents but unaffected by sulfhydryl or serine reagents and is devoid of esterase activity.