Cytochrome isoelectric point

According to Komai (85) crystalline Ustilago cytochrome c isolated by cell fracture rather than by alkaline extraction also displays a neutral isoelectric point. 

The effect of pH on the protein adsorption on CMK-3 was also investigated [152], The monolayer adsorption capacities obtained under various pH conditions are plotted in Figure 4.12, where the maximum adsorption was observed in the pH region near the isoelectric point of lysozyme (pi of about 11). Near the isoelectric point, the net charges of the lysozyme molecule are minimized and would form the most compact assembly. A similar pH effect was also seen in the adsorption of cytochrome c on CM K-3. Although the nature of the surface of mesoporous silica and... 

The molecular weight of cytochrome c peroxidase has been determined to be 34,100 on the basis of a sedimentation constant of 3.55 S, a diffusion constant of 9.44 F, and a partial specific volume of 0.733 ml/g (4 )-The enzyme exists as a monodisperse monomer containing one ferric protoporphyrin IX, which is noncovalently bound (/, , 14). No other transition metal is detected in crystalline preparations of the enzyme (22). The apoenzyme moiety is an acidic protein with an isoelectric point at pH... 

Davis et al. [89] reported an important work regarding the immobilization of metalloproteins and enzymes on oxidized, purified and vacuum-annealed SWCNTs in aqueous solution. AFM experiments showed that the immobilization is mainly physical, without need for covalent activation or electrostatic interaction. In fact, cytochrome c at pHs below the isoelectric point and ferritin at pHs above the isoelectric point showed an important adsorption obtained just by stirring the nanotubes dispersion (0.03 mg/mL) in dilute protein solutions (50-100 pg/mL) for a given time (2-20 h). GOx could be also adsorbed in a very efficient... 

A.26.5 (a) A has the lowest isoelectric point, so it is albumin B has the next lowest so it s P-lactoglobulin, and cytochrome c is C. (b) That it has a pi of about 10. (c) Electrophoresis would provide an estimate of molecular weight. Circular dichroism could provide an estimate of a-helix content. NMR and x-ray crystallography might be able to provide some structural information. 

The unusual independence of rate on reactant concentration clearly indicates that the cytochrome is intimately bound to the reaction-center complex. The binding mode between mammalian cytochrome c and the reaction center was revealed by the following experiments. Since a cytochrome has a high isoelectric point, it is present as a complex cation at neutral pH. The isoelectric point of the reaction-center complex is near 4.1, and therefore at neutral pH it would be present as a complex anion. Thus at pH 7.5, there should be a rather strong electrostatic attraction between the two. 

Subsequently Prince, Cogdell and Crofts also examined the reaction between Rp. sphaeroides reaction centers and mammalian cytochrome c as well as native cytochrome isolated from the same cells. They confirmed the electrostatic nature of the interaction between the Rp. sphaeroides reaction centers and mammalian cytochrome c. However, unlike the Rp. sphaeroides reaction center/mammalian cytochrome c system, the reaction with cytochrome isolated from Rp. sphaeroides is independent of pH between pH 4 and 10, and the effect of changing ionic strength on reaction rate is negligible at all pH values. The pH-independent behavior in this case has been attributed to the fact that the reaction-center complex and cytochrome have essentially the same isoelectric points, and thus similar overall charges at all pHs. 

Table 5.2 List of the cytochrome c fragments contained in the commercial digest sample with their sequence, mono-molecular weight, isoelectric point (pi) and hydrophobic character (log P, Kyte-Doolittle scale) calculated using Expasy software. ...

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