Lecture9 - MCB 110L Lecture 9 Prof Qing Zhong Selective...

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Unformatted text preview: MCB 110L Lecture 9 2/16/2011 Prof. Qing Zhong Selective precipitation - I • Fast, often ¡rst step after clari¡cation • Partitions based on solubility of target protein vs . that of contaminants. • Solubility determined by physico-chemical properties of solutes, unique for each protein • Salt is a common precipitant (poly-ethylene glycol is another) Precipitation - mechanism • Salt response of proteins is complex › Low salt: » Surface charges unshielded, can attract » Some proteins precipitate (typically observed at elevated [protein]) » “Salting in” +- +- + +- +- +- + +- +- +- + +- NaCl +--- + +- +- + +- +--- + Charged regions Hydrophobic patch Aggregated Dissociated Precipitation - mechanism (cont.) › High salt: » Ions compete for water, side chains → deplete hydration shell, neutralize surface charges » Promotes crowding, increases effective hydrophobicity → precipitation » “Salting out” + +--- + +- +- +- +- +- Am 2 SO 4 + +- +-- +- + +--- + +- +- +- +--- + +- + + +--- + +- +- Aggregated Dissociated- + Precipitation considerations [Salt] % Soluble Protein I Protein II Salting out Salting in • Different proteins have different charge and hydration characteristics • [Salt] needed to precipitate is empirical • Affecting factors ›Temperature...
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This note was uploaded on 09/12/2011 for the course MCB 120L taught by Professor Fairclough during the Spring '08 term at UC Davis.

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Lecture9 - MCB 110L Lecture 9 Prof Qing Zhong Selective...

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