Polystyrene protein denaturation

Ion exchange resins are also useful for demineralising biochemical preparations such as proteins. Removal of metal ions from protein solutions using polystyrene-based resins, however, may lead to protein denaturation. This difficulty may be avoided by using a weakly acidic cation exchanger such as Bio-Rex 70. 

The utilization of classical polystyrene particles or hydrophobic latexes for protein concentrations can induce undesirable phenomena such as protein denaturation and low concentration yields, on account of the high adsorption affinity between both species which may lead to a low desorbed amount. In addition, the use of such hydrophobic colloids in the polymerase chain reaction (PCR) of nucleic acid amplification step generally leads to total inhibition of the enzymatic reaction. The inhibition phenomena can be attributed to the denaturation of enzymes adsorbed in large numbers onto hydrophobic coUoids. The utilization of hydrophilic and highly hydrated latex particles (irrespective of temperature) is the key to solving this problem by suppressing the inhibition of enzyme activity. The purpose of this stage is then to focus on the potential apphcation of thermally responsive poly(NIPAM) particles for both protein and nucleic acid concentrations. 

The following protocol for passive adsorption is based on methods reported for use with hydrophobic polymeric particles, such as polystyrene latex beads or copolymers of the same. Other polymer particle types also may be used in this process, provided they have the necessary hydrophobic character to promote adsorption. For particular proteins, conditions may need to be optimized to take into consideration maximal protein stability and activity after adsorption. Some proteins may undergo extensive denaturation after immobilization onto hydrophobic surfaces therefore, covalent methods of coupling onto more hydrophilic particle surfaces may be a better choice for maintaining native protein structure and long-term stability. 

Figure 7.3 Characteristics of stationary phases used for gel filtration and GPC columns. (a) Graphs indicating the mass ranges for two phases in gel filtration and for three phases in gel permeation (b) Calibration curves (logM = /(V)) for these different phases obtained with proteins for gel filtration and with polystyrene standards for the others (known molecular weights). A weak slope from the linear section reveals a better resolution between neighbouring masses. This is the case when the pores are of regular dimension. The curves logM = f[K), more rarely studied, reveal the same aspect (reproduced courtesy of Tosohaas and Polymer Lab.). To avoid protein aggregate formation, denaturing compounds are sometimes introduced to the aqueous mobile phase.

Nareoja T, Maattwen A, Peltraien J et al (2009) Impact of surface defects and denaturation of capture surface proteins on nonspecific binding in immunoassays using antibody-coated polystyrene nanoparticle labels. J Immunol Methods 347 24—30... 

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