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Archaea, 2:51–57
© 2006 Heron Publishing—Victoria, Canada
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Purification and characterization of a thermostable, haloalkaliphilic extracellular serine protease from the extreme halophilic archaeon Halogeometricum borinquense strain TSS101

Malashetty Vidyasagar (1), S. Prakash (1), Carol Litchfield (2) and K. Sreeramulu (1, 3)

1. Department of Biochemistry, Gulbarga University, Gulbarga-585 106, Karnataka, India / 2. Department of Environmental Science and Policy, George Mason University, 10900 University Blvd., PW1 MS 4D4, Manassas, Virginia, 20110 / 3. Corresponding Author ([email protected]) / Received April 6, 2006; accepted May 23, 2006; published online June 19, 2006


A novel haloalkaliphilic, thermostable serine protease was purified from the extreme halophilic archaeon, Halogeometricum borinquense strain TSS101. The protease was isolated from a stationary phase culture, purified 116-fold with 18% yield and characterized biochemically. The molecular mass of the purified enzyme was estimated to be 86 kDa. The enzyme showed the highest activity at 60 °C and pH 10.0 in 20% NaCl. The enzyme had high activity over the pH range from 6.0 to 10.0. Enzymatic activity was strongly inhibited by 1 mM phenyl methylsulfonyl fluoride, but activity was increased 59% by 0.1% cetyltrimethylammonium bromide. The enzyme exhibited relatively high thermal stability, retaining 80% of its activity after 1 h at 90 °C. Thermostability increased in the presence of Ca2+. The stability of the enzyme was maintained in 10% sucrose and in the absence of NaCl.

Keywords: calcium chloride, cetyltrimethylammonium bromide, halophilic serine protease, metal ions, osmolytes, protease inhibitors.

 ISSN 1472-3654 (Online) ISSN 1472-3646 (Print) Copyright © 2002–2005 Heron Publishing