Protein isotherm

Figure 4.19 Example of single-protein isotherm in the presence of a salt, calculated using the ion-exchange formalism. Two-dimensional surface representation of the stationary phase concentrations of the protein (A) and the salt (S) as a function of their mobile phase concentrations. Reproduced with permission from A. Velayudhan and C. Horvdth, J. Chromatogr., 443 (1988) 13 (Fig. 2).

Figure 4.20 Multicomponent protein isotherms. Two-dimensional surface representations of the stationary phase concentrations of two proteins A and B as a fimction of their mobile phase concentrations at fixed concentration of mobile phase additive. A has an apparent charge of 10, B one of 6. Reproduced from A. Velayudhan and Cs. Horvath, J. Chromatogr., 443...

Smith, B. A., and Sefton, M. V., 1992, Thrombin and albumin adsorption to PVA and heparin-PVA hydrogels. I. Single protein isotherms, J. Biomed. Mater. Res. 26 947-958. 

From the surface tension isotherms reported it can be generalized that interactions between protein and amphiphile in the bulk solution are closely related to adsorption behaviour at the air/water interface. Association of lipid-like substances to proteins results in plateau regions of the isotherms, within which neither changes in the amphiphile concentration, nor the supposed consecutive unfolding of the protein structure is reflected in the zly-value. Replacement of protein in the surface film by a lipid type of amphiphile, when no interaction occurs, was seen in the mono-caproin-ovalbumin isotherm, and also in the SDS-protein isotherms at sufficiently high amphiphile concentrations. Similar effects have also been observed in the membrane of the fat globule in milk [24], by addition of a nonionic amphiphile at emulsification. 

The effect of temperature on K can be seen by comparing protein isotherms conducted at 52°C with those conducted at 27°C. For both ) -Lag and BSA, K increased with temperature (Table 5). Applying the van t Hoff equation,... 

Proteins often have the same high-affinity isotherms as do synthetic polymers and are also slow to equilibrate, due to many contacts with the surface. Proteins, however, have the additional complication that they can partially or completely unfold at the solid-liquid interface to expose their hydrophobic core units to a hydrophobic surface... 

Folded proteins can be caused to spontaneously unfold upon being exposed to chaotropic agents, such as urea or guanidine hydrochloride (Gdn), or to elevated temperature (thermal denaturation). As solution conditions are changed by addition of denaturant, the mole fraction of denatured protein increases from a minimum of zero to a maximum of 1.0 in a characteristic unfolding isotherm (Fig. 7a). From a plot such as Figure 7a one can determine the concentration of denaturant, or the temperature in the case of thermal denaturation, required to achieve half maximal unfolding, ie, where... 

Fig. 7. Unfolding (a) isotherm, where the half-maximal unfolding for this protein occurs at 2.6 M denaturant and (b) free energy where in the absence of denaturant, the protein has an extrapolated stability,, of 17.6 kj/mol (4.2 kcal/mol) as shown. To convert to cal, divide by 4.184.

Fig. 16. Isotherms of protein bonding by nonionized CP (a = 0) /) lysozyme — MA-EDMA (2.5 mol%) copolymer 2) haemoglobin — MA-EDMA (2.5mol%) copolymer 3) haemoglobin - AA-EDMA (2.5mol%) copolymer 4) haemoglobin — MA-EDMA (2.5 mol%)gr. copolymer 5) serum albumin — MA-EDMA (2.5 mol%) copolymer. Ceq...

Since the preparation of the PEO and PVP silicas was carried out under the circumstances corresponding to the plateau part of isotherms, it obviously led to tailed structures of the stationary phases. Their inherent repellency ensured the size-exclusion mechanism for chromatography of viruses and large proteins. 

This precipitation process can be carried out rather cleverly on the surface of a reverse phase. If the protein solution is brought into contact with a reversed phase, and the protein has dispersive groups that allow dispersive interactions with the bonded phase, a layer of protein will be adsorbed onto the surface. This is similar to the adsorption of a long chain alcohol on the surface of a reverse phase according to the Langmuir Adsorption Isotherm which has been discussed in an earlier chapter. Now the surface will be covered by a relatively small amount of protein. If, however, the salt concentration is now increased, then the protein already on the surface acts as deposition or seeding sites for the rest of the protein. Removal of the reverse phase will separate the protein from the bulk matrix and the original protein can be recovered from the reverse phase by a separate procedure. 

Why is myoglobin unsuitable as an O2 transport protein but well suited for O2 storage The relationship between the concentration, or partial pressure, of O2 (PO2) and the quantity of O2 bound is expressed as an O2 saturation isotherm (Figure 6-4). The oxygen-... 

For instance, the time course of SPE demonstrates that the solvent phase surfactant concentration steadily decreases (Fig. 3) [58]. The w/o-ME solution s water content decreases at the same rate as the surfactant [58]. The protein concentration at first increases, presumably due to the occurrence of Steps 2 and 3 above, but then decreases due to the adsorption of filled w/o-MEs by the solid phase (Fig. 3) [58]. Additional evidence supporting the mechanism given above is the occurrence of a single Langmuir-type isotherm describing surfactant adsorption in the solid phase for several SPE experiments employing a given protein type (Fig. 4) [58]. Here, solid-phase protein molecules can be considered as surfactant adsorption sites. Similar adsorption isotherms occurred also for water adsorption [58]. 

We studied the surface pressure area isotherms of PS II core complex at different concentrations of NaCl in the subphase (Fig. 2). Addition of NaCl solution greatly enhanced the stability of monolayer of PS II core complex particles at the air-water interface. The n-A curves at subphases of 100 mM and 200 mM NaCl clearly demonstrated that PS II core complexes can be compressed to a relatively high surface pressure (40mN/m), before the monolayer collapses under our experimental conditions. Moreover, the average particle size calculated from tt-A curves using the total amount of protein complex is about 320 nm. This observation agrees well with the particle size directly observed using atomic force microscopy [8], and indicates that nearly all the protein complexes stay at the water surface and form a well-structured monolayer. 

Our studies on the surface pressure-area isotherms of MGDG and the mixture of PS II core complex and MGDG indicate the presence of both PS II core complex and MGDG in the monolayer. MGDG molecules diluted the PS II core complex concentration in the monolayer. MGDG lipid functions as a support for the protein complex and the resulting mixture forms higher-quality films than PS II core complex alone. 

Chang, C. and Lenhoff, A.M., Comparison of protein adsorption isotherms and uptake rates in preparative cation-exchange materials, ]. Chromatogr. A, 827, 281, 1998. 

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