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Physical & Chemical properties

Water solubility

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Endpoint:
water solubility
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other justification
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Description of key information

The solubility of 4 -phytase is generally between 1 and 100g/L in tap water (moderate salinity at pH 7 or just below).

Increasing pH generally leads to higher solubility.

Key value for chemical safety assessment

Water solubility:
100 g/L
at the temperature of:
25 °C

Additional information

The solubility of enzymes in purified water at pH 7 is between 1 and 100 g/l. The degree of solubility at a given pH is depending on the conditions (temperature, the amino acid sequence and structure of the enzyme and other components in the system such as salts). The amino acid sequence and structure affect the polarity of the enzyme, and are important factors for solubility. Thus, the variance in solubility is a reflection of the variation in the amino acid sequence. Enzymes generally have the lowest solubility when the pH is close to isoelectric point (+/- 1 pH unit) and the solubility increases when pH is shifting away from isoelectric point. This generally holds true as long as the pH does not denature the enzyme structure. The isoelectric point of industrial phytases ranges from 3.58 to 7.04. Post translational modifications also influence the solubility. The most relevant modification is glycosylation, which typically increases the solubility.

 

The influence of pH and salt concentration on protein stability has been investigated in the following publications (Carbannaux et al., 1995; Green, 1932; Guilloteau et al., 1992; Hofmeister 1888). The effects of anions and cations on protein solubility in general are described by the Hofmeister series (Hofmeister 1888). These concepts may not be directly applicable to highly purified enzymes like industrially manufactured phytases. However, these concepts indicate that the solubility of proteins, like enzymes, is dependent on the conditions in a given environment.

 

The conclusion is that the water solubility differs between different phytases, due to difference in amino acid sequence and presence of post translational modifications. Water solubility is also highly dependent on the aqueous environment, i.e. pH, salts present, temperature and stabilizing agents, and it is thus not possible to give one water solubility value for all industrial produced phytases. Industrial enzymes are produced in submerged fermentation followed by downstream purification. The final product is a mixture of the enzyme, other constituents from the fermentation and stabilizing agents that are added in the downstream processing. On this background the solubility data generated are based either on finished products or enzymes purified in buffer and salts and not in purified water alone.

 

References:

Carbonnaux, C., Riès-Kautt, M., & Ducruix, A., (1995);Protein Science,4, 2123 -2128.

Faber, C., (2006); PhD-thesis ‘Measurement and Prediction of Protein Phase Bahaviour and Protein-Protein-Interactions’ at the Center for Microbial Biotechnology, Biocentrum-DTU, Technical University of Denmark.

Green, A. A., (1932);Physical Chemistry of Proteins,10, 47-66.

Guilloteau, J. P., Riès-Kautt, M., & Ducruix, A., (1992);Journal of Crystal Growth,122, 223-230.

Hofmeister, F., (1888);Archiv für experimentelle Pathologie und Pharmakologie,24,247-260.