Protein induced desorption

Sundqvist, B. Hakansson, P. Kamensky, I. Kjellberg, J. Ion Formation from Organic Solids Fast heavy ion induced desorption of molecular ions from small proteins. Benninghoven, A. Springer Series in Chemical Physics 1983, 25, 52-57. 

Welin-Klinstroem et al used a null ellipsometer equipped with an automatic sample scanning device for studies of adsorption and desorption of fibrinogen and IgG at the liquid/solid interface on surface wettability gradients on silicon wafers. To follow the processes along the wettability gradient, off-null ellipsometry was used. The kinetics of adsorption and nonionic-surfactant-induced desorption varied considerably between fibrinogen and IgG. In the hydrophilic region, veiy little protein desorption was seen when a nonionic surfactant was used. 

Surface-induced change in conformation which optimizes protein-surface interaction and decreases the probability for desorption ... 

FIGURE 7 Group B streptococcus infection-induced differential protein expression in nonhuman primate (A) and human (B) amniotic fluid samples by surface-enhanced laser desorption/ionization (SELDI-TOF MS) using normal-phase protein chip arrays. Spectrum from 2.5 to 15 kDa collected at 235 nm laser intensity. Detailed spectra show increased expression of the 3.5 and 10.8 kDa peaks between control and infected. Arrows indicate the unique peaks represented by polypeptides overexpressed in infection. 

A change in the hydrophilic nature of the polymer surface on irradiation of poly-(p-phenylazoacrylanilide) (PAAn) or its copolymer with HEMA may be used to control the adsorption — desorption behavior of proteins or organic substances onto the polymer [49]. Adsorption of lysozyme onto the copolymer of p-phenylazo-acrylanilide and HEMA was foimd to decrease from 4.6 eg to 1.8 eg per gram of adsorbent on ultraviolet irradiation, which induces the isomerization from the trans to the cis form. The decrease in adsorption ability upon ultraviolet irradiation is explained by a reduction of the hydrophobic interaction between the protein and the polymer, which results from the appearance of hydrophilic cw-form azobenzene on the surface. 

For practical applications, essentially irreversible adsorption is required to prevent leaching, or desorption, which leads to activity loss. Optimum conditions are determined empirically, by varying pH, temperature, ionic strength, and quantities of protein and adsorbent. Desorption of enzymes may also be substrate induced, where high substrate concentrations cause leaching due to conformational changes. 

Hemoproteins are a broad class of redox-proteins that act as cofactors, e.g. cytochrome c, or as biocatalysts, e.g. peroxidases. Direct ET between peroxidases such as horseradish peroxidase, lactoperoxidase," or chloropcroxidasc"" and electrode surfaces, mainly carbonaceous materials, were extensively studied. The mechanistic aspects related with the immobilized peroxidases on electrode surfaces and their utilization in developing biosensor devices were reviewed in detail. The direct electrical contact of peroxidases with electrodes was attributed to the location of the heme site at the exterior of the protein that yields close contact with the electrode surface even though the biocatalyst is randomly deposited on the electrode. For example, it was reported " that non-oriented randomly deposited horseradish peroxidase on a graphite electrode resulted in 40-50% of the adsorbed biocatalyst in an electrically contacted configuration. For other hemoproteins such as cytochrome c it was found that the surface modification of the electrodes with promoter units such as pyridine units induced the binding of the hemoproteins in an orientation that facilitated direct electron transfer. By this method, the promoter sites induce a binding-ET process-desorption mechanism at the modified electrode. Alternatively, the site-specific covalent attachment of hemoproteins such as cytochrome c resulted in the orientation of the protein on the electrode surfaces and direct ET communication. ... 

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