TAILIEUCHUNG - Protein Purification Part 4

Tham khảo tài liệu 'protein purification part 4', khoa học tự nhiên, công nghệ sinh học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 38 Protein Purification sample as possible in the fewest number of isolation steps. In this project invertase is purified from a 25 mL sample of fresh yeast extract by i differential precipitation with ethanol ii gel filtration and iii ion-exchange chromatography. Precipitation of invertase with ethanol The selective precipitation of a protein from an aqueous solution is one of the oldest most effective and technically simple isolation steps used in protein purification. Furthermore the solid protein precipitated from a large volume of extract can also be concentrated by dissolving it back into a much smaller volume of solvent that is more convenient to apply to a variety of chromatography columns used in subsequent isolation steps. For this reason it is not uncommon for protein precipitation to be used as the initial isolation step of many purification procedures. In order for a large protein molecule to become solvated or dissolved in an aqueous solution the majority of its surface must be able to form complexes with an enormous number of water molecules producing a large hydration shell that is energetically stabilized by ion-dipole hydrogen bonds and dipole-dipole attractive forces between the water molecules and side chains of polar amino acids exposed on the protein s surface. Because these interactions with the water molecules . the hydration shell energy required to keep a protein solvated are sensitive to the pH ionic strength and polarity of the solvent AND because each protein has a unique hydration shell network it is possible to selectively entice the surfaces of specific proteins in a mixture to become less and less hydrated such that their newly exposed surfaces are forced to stick or clump together into an insoluble aggregate or precipitate by simply adding a high enough concentration of an acid to lower the pH of the solvent or a salt to increase the ionic strength of the solvent or an organic liquid to decrease the polarity of the solvent .

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