© 2005 The Japanese Biochemical Society
Regular Paper |
Purification and Characterization of a Novel Sialidase from a Strain of Arthrobacter nicotianae
1 Institute of Microbiology, Bulgarian Academy of Sciences, 1113 Sofia, G. Bonchev 26, Bulgaria; 2 Institute of Organic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, G. Bonchev 9, Bulgaria; and 3 Abteilung für Physikalische Biochemie, Physiologisch-chemisches Institut der Universität Tübingen, Hoppe-Seyler-Straße 4, D-72076 Tübingen, Germany
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ABSTRACT
The nonpathogenic strain Arthrobacter nicotianae produces two sialidase isoenzymes, NA1 and NA2, with molecular masses of 65 kDa and 54 kDa, respectively, as determined by 10% SDS–polyacrylamide gel electrophoresis. NA1 and NA2 exhibit maximum activities at pH 4 and 5, and both show clear thermal optima at 40°C. They are stable at temperatures up to 50°C. The critical temperatures (T c = 50°C and 51°C) for the two isoenzymes were determined by fluorescence spectroscopy and correlate well with the temperatures of melting (T m = 49°C and 48°C), determined by CD spectroscopy. The isoenzymes are less stable against denaturation with Gdn.HCl, and the free energy of stabilization in water was calculated to be 7.6 and 8.0 kJ mol–1, respectively. The specific activity (K m value) toward glucomacropeptide as a substrate was calculated to be 0.126 mM for NA1 and 0.083 mM for NA2.