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Applied and Environmental Microbiology, November 1998, p. 4446-4451, Vol. 64, No. 11
Vitamins and Fine Chemicals Division,
Received 6 May 1998/Accepted 23 August 1998
Enzymes that are used as animal feed supplements should be able to
withstand temperatures of 60 to 90°C, which may be reached during the
feed pelleting process. The thermostability properties of three
histidine acid phosphatases, Aspergillus fumigatus phytase, Aspergillus niger phytase, and A. niger optimum
pH 2.5 acid phosphatase, were investigated by measuring circular
dichroism, fluorescence, and enzymatic activity. The phytases of
A. fumigatus and A. niger were both denatured
at temperatures between 50 and 70°C. After heat denaturation at
temperatures up to 90°C, A. fumigatus phytase refolded
completely into a nativelike, fully active conformation, while in the
case of A. niger phytase exposure to 55 to 90°C was associated with an irreversible conformational change and with losses
in enzymatic activity of 70 to 80%. In contrast to these two phytases,
A. niger pH 2.5 acid phosphatase displayed considerably higher thermostability; denaturation, conformational changes, and
irreversible inactivation were observed only at temperatures of
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Comparison of the Thermostability Properties of
Three Acid Phosphatases from Molds: Aspergillus fumigatus
Phytase, A. niger Phytase, and A. niger
pH 2.5 Acid Phosphatase
80°C. In feed pelleting experiments performed at 75°C, the recoveries of the enzymatic activities of the three acid phosphatases were similar (63 to 73%). At 85°C, however, the recovery of
enzymatic activity was considerably higher for A. fumigatus
phytase (51%) than for A. niger phytase (31%) or pH 2.5 acid phosphatase (14%). These findings confirm that A. niger pH 2.5 acid phosphatase is irreversibly inactivated at
temperatures above 80°C and that the capacity of A. fumigatus phytase to refold properly after heat denaturation may
favorably affect its pelleting stability.
*
Corresponding author. Mailing address: F. Hoffmann-La
Roche Ltd., Vitamins and Fine Chemicals Division, Biotechnology
Section, Bldg. 93/456, CH-4070 Basel, Switzerland. Phone:
41-61-688-2972. Fax: 41-61-688-1645. E-mail:
markus.wyss{at}roche.com.
Applied and Environmental Microbiology, November 1998, p. 4446-4451, Vol. 64, No. 11
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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