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Isolation and properties of a staphylococcal protease, preferentially cleaving glutamoyl-peptide bonds.

An extracellular protease of a mutant of strain 8325N of Staphylococcus aureus, was isolated by a three-step procedure involving stepwise chromatography on DEAE-cellulose, gradient chromatography on hydroxyapatite and gel filtration on Sephadex G-150. The enzyme was purified 250 times to homogeneity with a recovery of 20–30%. 
 
 
 
The protease has a molecular weight of about 29000 and consists of a single polypeptide chain as shown by gel filtration of native enzyme on calibrated columns of Sephadex G-150 as well as gel filtration of denaturated enzyme on Sepharose 6-B in 6 M guanidine-HCl and dodecylsulfate-polyacrylamide gel electrophoresis. Peptide maps also suggest a molecular weight around 30000. It is an acidic protein and is rich in aspartic acid and asparagine, but no cysteine or cystine can be detected. The N-terminal sequence is Val-Ile-Leu-Pro-Asn-Asn-Asp. The enzyme contains no carbohydrate. 
 
 
 
The protease preferentially hydrolyzes peptide bonds on the carboxyl-terminal side of glutamic acid. In a few cases aspartoyl bonds were also cleaved. It has no activity towards dipeptides with N-terminal glutamic acid. The activity was not affected by divalent cations or EDTA, but was completely abolished after incubation with diisopropylfluorophosphate suggesting that the enzyme is a serine protease. 
 
 
 
The purified enzyme is stable between pH 3 and 10. It has maximum activity between pH 7.5 and 7.8 with casein as substrate and between pH 4.5 and 5.0 with hemoglobin as substrate.