Hydrophobic regions cytochrome

As an example of the techniques/ Figure 4 shows a comparison of the fungicidally active RR- diclobutrazol with the natural substrate lanosterol. The sterol C-32 alcohol is chelated to the iron porphyrin. The three central features of the model cytochrome P-450 can be elucidated. The hydrophobic binding site, the polar region between this hydrophobic region and the heme plane/ and a common complexation to the porphyrin iron. 

The reaction between HiPIP and cytochrome c or bacterial cytochromes784 involves specific sites on both proteins, although no kinetic evidence for association was found. Reaction between Chr. vinosum and Rhodopseudomonas gelatinosa HiPIPs with modified cytochrome c (trinitro-phenyllysine-13)785 was more rapid than for the unmodified cytochrome c since modification of Lys-13 destabilizes the heme crevice, and because the hydrophobic TNP group facilitates electron transfer by interacting with a hydrophobic region of the HiPIP. 

Hase,T., Harabayashi, M., Kawai, K., and Matsubara, H., 1987, A carboxylnterminal hydrophobic region of yeast cytochrome Cj is necessary for functional assembly into complex III of the respiratory chain, J. Biochem. (Tokyo) 102 411n419. 

Fig. 6, left shows an end view of a type-I crystal formed by stacking two-dimensional crystal layers, ordered sheets of proteins. Many proteins, but not all, can form such a two-dimensional crystal layer, in which the hydrophobic regions of the proteins interact with the hydrocarbon tails of the lipids, the two-dimensional structure being stabilized by both hydrophobic and polar interactions. In each two-dimensional crystal layer no detergent is present and only the polar domains are exposed at the surface. These two-dimensional crystal layers then stack up to form a three-dimensional crystal through polar attractions between the layers. In three-dimensional crystals, the successive two-dimensional crystal layers need to be ordered in the third dimension with respect to translation, rotation and up-down orientation. Examples of type-I crystals which have been prepared are mitochondrial cytochrome oxidase, chloro-plastChl-a/ proteins, and a protein from the purple membrane ofhalobacteria. Two-dimensional crystals are usually rather small and useful only for examination by electron microscopy. 

Topography No doubt the importance of phospholipids in the activity of the CYPs resides in their role as membrane lipids orienting GYP enzymes within the ER membrane. The hydrophobic region near the N-terminal end of the protein is the membrane-spanning domain and presumed to be an a-helix. The orientation of cytochrome P450 within the ER membrane has been depicted as in Eigure 8.10. 

The Hydrophobic Effect - interactions between hydrophobic regions of a protein, which actually increase entropy by destroying the ordered clathrate structures of water around these residues in the unfolded state. The hydrophobic effect is sometimes incorrectly called hydrophobic bonding. Table 6.4 shows numerical values assigned to the relative hydrophobicities of the amino acids. In Table 6.3, the hydrophobic effect can be seen by the more positive AS values for cytochrome c and myoglobin. 

The kinetics of electron transfer reactions between spinach plastocyanin and [Fe(CN)6] ", [Co(phen)3] , and Fe(II) cytochrome c have been studied as a function of ionic strength. Applications of the equations of Van Leeuwen support the proposal of two sites of electron transfer, with [Co(phen)3] binding near residues 42-45 and the interaction of [Fe(CN)6] at a hydrophobic region near the copper ion. Pulse radiolysis has been employed to measure the rates of electron transfer from Ru(II) to Cu(II) in plastocyanins from Anabaena variabilis and Scenedesmus obliquus which have been modified at His-59 by [Ru(NH3)5] . The small intramolecular rates (<0.082 and <0.26 s , respectively) over a donor-acceptor distance of 12 A indicate that electron transfer from the His-59 site to the Cu center is not a preferred pathway. A more favorable route, via the acidic (residues 42-44) patch ( 14 A to Cu), is supported by the rate of >5 x 10 s for the reduction of PCu(II) by unattached [Ru(NH3)5im] . The intramolecular electron transfer from Fe(II) in horse cytochrome c to Cu(II) in French bean plastocyanin ( 12 A from heme edge to Cys-84 S), in a carbodiimide cross-linked covalent complex, proceeds with a rate of 1.05 x 10 s . The presence of the... 

Other examples documenting the direct interaction between hydrophobic regions accessible on the surface of a protein and the corresponding nonpolar ligates on the stationary phase of a RPC or HIC sorbent have been described in the scientific literature. For example, as noted earlier, the hydrophobic contact site of equine cytochrome c and porcine growth hormone in the presence of /i-butyl ligands has been delineated [140,141] using a combination of footprint enzymatic procedures and electrospray mass spectrometry. A less direct approach is based... 

The L and the M subunits are firmly anchored in the membrane, each by five hydrophobic transmembrane a helices (yellow and red, respectively, in Figure 12.14). The structures of the L and M subunits are quite similar as expected from their sequence similarity they differ only in some of the loop regions. These loops, which connect the membrane-spanning helices, form rather flat hydrophilic regions on either side of the membrane to provide interaction areas with the H subunit (green in Figure 12.14) on the cytoplasmic side and with the cytochrome (blue in Figure 12.14) on the periplasmic side. The H subunit, in addition, has one transmembrane a helix at the car-boxy terminus of its polypeptide chain. The carboxy end of this chain is therefore on the same side of the membrane as the cytochrome. In total, eleven transmembrane a helices attach the L, M, and H subunits to the membrane. 

Fig. 18. Schematic representation of the transmembrane orientation of cytochrome f based on the occurrence of a high proportion of charged residues for 1—250 (represented as a globular region), and hydrophobic residues 250-271 (believed to be helical and trans-membrane) [146]...

The entire iron-porphyrin-protein complex is called a cytochrome and such proteins are important electron-transfer components of cells. Generally, access to the macromolecular region in which the oxidation reactions occur is via a hydrophobic channel through the protein (Mueller et al., 1995). As a result, organic substrates are transferred from aqueous solution into the enzyme s active site primarily due to their hydrophobicity and are limited by their size. This important feature seems very appropriate hydrophobic molecules are selected to associate with this enzyme, and these are precisely the ones that are most difficult for organisms to avoid accumulating from a surrounding aquatic environment. 

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