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Applied and Environmental Microbiology, September 1999, p. 3969-3975, Vol. 65, No. 9
Area de Microbiologia, Departamento de
Biología Funcional, Facultad de Medicina, IUBA, Universidad
de Oviedo, 33006 Oviedo, Spain
Received 11 March 1999/Accepted 8 July 1999
A novel protease, hydrolyzing azocasein, was identified, purified,
and characterized from the culture supernatant of the fish pathogen
Yersinia ruckeri. Exoprotease production was detected at
the end of the exponential growth phase and was temperature dependent.
Activity was detected in peptone but not in Casamino Acid medium. Its
synthesis appeared to be under catabolite repression and ammonium
control. The protease was purified in a simple two-step procedure
involving ammonium sulfate precipitation and ion-exchange chromatography. Sodium dodecyl sulfate-polyacrylamide gel
electrophoresis (SDS-PAGE) analysis of the purified protein indicated
an estimated molecular mass of 47 kDa. The protease had characteristics
of a cold-adapted protein, i.e., it was more active in the range of 25 to 42°C and had an optimum activity at 37°C. The activation energy
for the hydrolysis of azocasein was determined to be 15.53 kcal/mol,
and the enzyme showed a rapid decrease in activity at 42°C. The
enzyme had an optimum pH of around 8. Characterization of the protease
showed that it required certain cations such as Mg2+ or
Ca2+ for maximal activity and was inhibited by EDTA,
1,10-phenanthroline, and EGTA but not by phenylmethylsulfonyl fluoride.
Two
N-methyl-N-nitro-N-nitrosoguanidine mutants were isolated and analyzed; one did not show caseinolytic activity and lacked the 47-kDa protein, while the other was
hyperproteolytic and produced increased amounts of the 47-kDa protein.
Azocasein activity, SDS-PAGE, immunoblotting by using polyclonal
anti-47-kDa-protease serum, and zymogram analyses showed that protease
activity was present in 8 of 14 strains tested and that two Y. ruckeri groups could be established based on the presence
or absence of the 47-kDa protease.
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Purification and Characterization of an Extracellular Protease
from the Fish Pathogen Yersinia ruckeri and Effect
of Culture Conditions on Production
*
Corresponding author. Mailing address: Area de
Microbiologia, Departamento de Biología Funcional, Facultad de
Medicina, Universidad de Oviedo, 33006 Oviedo, Spain. Phone:
34985104218. Fax: 34985103148. E-mail:
JAGA{at}sauron.quimica.uniovi.es.
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