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Physical & Chemical properties

Water solubility

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Reference
Endpoint:
water solubility
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other justification
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Description of key information

The solubility of enzymes is generally between 0.5 and 250 g/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:
125 g/L
at the temperature of:
25 °C

Additional information

The solubility of trypsins in purified water at pH 7 is between 0.5 and 250 g/L.

The degree of solubility at a given pH is depending on several factors, e.g. 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, including the isoelectric point (pI) of the enzyme, which is an important factor for solubility. Thus, the difference in solubility is a reflection of the variation in the amino acid sequence. In addition, post translational modifications influence solubility, where the most important is glycosylation, which typically increases the solubility. The influence of pH and salt concentration on protein stability has been investigated (Carbannaux et al., 1995; Green, 1933; 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). All indicate that the solubility of proteins like enzymes is dependent on the conditions in a given environment.

Enzymes generally have the lowest solubility when the pH is close to pI (+/- 1 pH unit) and the solubility increases when pH is shifting away from pI, as long as the pH is not denaturing the enzyme. The pI of trypsins ranges from 3 -6.9 (http://www.brenda-enzymes.info/). Studies on different enzymes covering alpha-amylases (Faber et al., 2007) and proteases (HERA, 2007)* show high solubility (60 -100 g/L) at pH between 6 to 8.

The conclusion is that the water solubility differs between different enzymes within the same class, 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 enzymes but only a range. 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. In general, solubility data 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(10):2123 -2128.

Green AA. (1932). Physical Chemistry of Proteins. 10:47-66.

Guilloteau J P, Riès-Kautt M, Ducruix A. (1992). Variation of lysozyme solubility as a function of temperature in the presence of organic and inorganic salts. J. Crystal Growth, 122(1 -4):223-230.

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

Faber C, Hobley TJ, Mollerup J, Thomas ORT and Kaasgaard SG. (2007). Study of the Solubility of a Modified Bacillus licheniformis α-Amylase around the Isoelectric Point. J. Chem. Eng. Data, 52:707-713

HERA (Human & Environmental Risk Assessment) on ingredients of household cleaning products, (2007); Subtilisins (Protease) CAS No: 9014-01-1, 1395-21-7, 9073-77-2, 9001-92-7, 79986-26-8, 95979-76-3, 68909-17-1. *NOTE: Data published in HERA 2007 as “> 1 kg/L”, but has to be corrected to “> 100 g/L”.