Protein rearrangement

Perhaps the most Important effect of conformational variations In electron transfer reactions would be to alter the distances and the relative orientations of donors and acceptors. In photosynthetic RC s, where the primary donors and acceptors lie within 4-5A of each other ( ), small structural displacements (, 5A) may significantly affect rates of back reactions. If they occur rapidly (24), (Conformational movements on a picosecond time scale are not Inconsistent with resonance Raman data on photo-dlssoclated heme-CO complexes (25)), On a longer time scale, protein rearrangements triggered by and propagating from the chromophores may also help subsequent reactions such as the transport of protons that Is Initiated by the primary photochemical event In the R,C, (26),... 

By thermal and shear forces during extrusion which cause protein rearrangement/degradation, the Maillard reaction progresses, and a wide variety of potent flavoring compounds can result. Reaction rates in turn are influenced by the types of sugars and amino acids present, temperature, water activity, duration of heating, and pH. 

Loots, E., and Isacoff, E. Y (1998). Protein rearrangements underlying slow inactivation of the Shaker K+ channel./. Gen. Physiol. 112, 377-389. 

Aconitase is currently the only well-characterized example of a cubane-type [3Fe-4S]+ to linear [3Fe-4S]+ cluster conversion. This remarkable transformation occurs at pH > 9.5 or under conditions of partial denaturation, despite requiring a major protein rearrangement. Only two of the cysteine ligands to the cubane-type [3Fe-4S]+ cluster... 

The reduction of ferricytochrome c by at neutral pH appears to be a three-step process. In the first step (A =4.5x 10 lmol- s ) a transient complex is formed between the cytochrome and the hydrated electron, in the second (k= 5 X 10 s ) the haem iron is reduced, and in the third (/ = 1.3 x 10 s ) the protein conformation changes from that appropriate for Fe to that appropriate for Fe. The authors favour a specific pathway for the movement of the electron from the surface of the molecule to the haem iron (step 1). No intermediate complexes were observed in the reduction of ferricytochrome c by the superoxide radical ion. At 20 °C the rate constant for the reaction at pH 4.7—6.7 is 1.4 x 10 1 mol s and as the pH increases above 6.7 the rate constant steadily decreases (eventually reaching zero, indicating that the neutral and high-pH forms if ferricytochrome c are un-reactive). The activation enthalpy is 18 kJ mol and it seems that little protein rearrangement is required for the formation of the activated complex. The kinetics have been reported for the reduction by Cr + of 2-hydroxy-5-nitrobenzyltryptophyl cytochrome c and of iV-formyltryptophyl cytochrome c. ... 

Rupture of low-energy intermolecular bonds stabilising systems in the native state, protein rearrangement. 

The following steps are required to form a material from a protein concentrate or extract (i) scission of low-energy intermolecular bonds stabilizing systems in the native state, (ii) protein rearrangement, and (Hi) the formation of a 3-dimensional network stabilized by new interactions or linkages, after removal of the intermolecular bond scission agent. 

Proteins have complex molecular structures. The linear sequence of the amino acids comprising a protein is classified as its primary structure. In different proteins, these linear sequences assume conserved structures along the axis of the polypeptide in the form of alpha-helixes, 3j -helix, beta sheets, or random coils, turns which are described as the secondary structure of the protein. These secondary structures are stabilized primarily by hydrogen bonds. For thermodynamic stability, proteins rearrange themselves into tertiary structures comprising several secondary structures stabilized by van der Waal s, electrostatic, or hydrophobic interactions, hydrogen bonding, as well as disulfide cross-links. Some proteins have a fourth structural level called the quaternary structure in which two or more... 

The activity of an adsorbed protein depends upon the orientation and conformation of the protein molecule on material surface. Sometimes, the protein shows structural rearrangements with time (such as transformation of an a-helix structure to a random coil one), which may either cause strengthening of protein attachment or lead to reversible adsorption and protein elution. Thus, the stability of a protein conformation governs the kinetics of its adsorption. Depending upon the type of application, either of the protein rearrangements may be favorable. The adsorption profile and functionality of the protein determines the protein mediated cell responses. From literature, it is unclear on the optimum surface chemistry necessary for a desired cellular... 

The limiting value at C2 0 is usually taken as the partial specific volume, v , of the macro-molecular component 2 (e.g., protein). Rearrangement of Eq.(6) and evaluation of the limiting slope,... 

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