I’m doing an internship at the Cargill company and work a lot with proteins here. I have placed gluten here in different beakers with water with different Ph’s apparently gluten dissolves strongly at an acidic Ph and at a Ph of 8 the least after that the gluten dissolves more and more. Is this correct or does the solubility also have to do with pressure temperature etc etc.
Answer
Dear William,
The pH is indeed an important parameter in the solubility of proteins. The pH at which the solubility is best depends mainly on the amino acid composition. The general rule is that solubility is minimal when pH=pI. Proteins with many acidic amino acids have a low pI and are therefore poorly soluble at pH 4 to 5, for proteins with basic amino acids this will be more likely at pH 8-9. In addition, the solubility also strongly depends on the salt content and the type of salt added. Proteins are poorly soluble in pure water, from 50 to 500 mM salt the solubility is generally high (NaCl in particular helps to keep proteins in solution), above that you get salting out effects, especially with sulfates for example.
Pressure and temperature do indeed have an influence. The effect of pressure only comes into play at very high pressure. As far as temperature is concerned, you have to take into account that proteins above 60 degrees Celsius usually start to denature (and therefore usually also precipitate), but here too this is strongly protein-dependent.
Answered by
prof. Bart Devreese
Biochemistry, Biochemical Analysis proteins
http://www.ugent.be
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