Co -protoporphyrin

As described later, hemopexin interacts with a variety of heme analogs, two of which, Sn-protoporphyrin IX (SnPP) and Co-protoporphyrin IX (CoPP), helped clarify the mechanism of MT-1 gene regulation by hemopexin. SnPP-hemopexin interacts with the hemopexin receptor and the SnPP (an inhibitor of HO-1, (91)) enters the cell and induces HO-1 (92). In contrast, CoPP-hemopexin interacts with the receptor, but CoPP is not internalized. Interestingly, the mere occupancy of the receptor by hemopexin is sufficient to activate signaling pathways and consequent induction of MT-1 (90, 92, 93), whereas heme uptake is required for activation of HO-1 gene transcription (92, 93). 

Formation constants for the binding of axial ligands have been reported for many systems, for example pyridine with Fe" and Fe " tetraphenylporphyrin, other Fe porphyrins and Co" protoporphyrin IX dimethyl ester. Kinetic studies on the binding of axial ligands are also available. ... 

As starting point for our calculations, we have used the following PDB files for structures Fe-protoporphyrin PDB Code HEM, Co-protoporphyrin PDB Code COH, Mg-protoporphyrin PDB Code HEG, Ni-protoporphyrin PDB Code HNl, Zn-protoporphyrin PDB Code ZNH [45] and Cambridge Crystallographic Data Centre for Ca-protoporphyrin [46]. 

Fig. 44. I vs. 0) curves in an 02-saturated 0.05 M H2SO4 solution at graphite rotating disc (modified by Co-protoporphyrin) with a Pt ring. Reduction on the disc at (1) -f-0.1, (2) 0.0, (3) —0.4 V vs. SCE oxidation at constant ring-potential +I.0V. Adapted from [142].

FIGURE 3.4 The ovine Co -COX-1 (PGHS-1) enzyme with arachidonic acid (8) in the COX channel (PDB IDIY). (a) Structural overview showing the domains of monomeric COX-1, (b) The peroxidase active site of COX-1 with arachidonic acid (8), important nearby residues, and the Co +-protoporphyrin IX. Phe209 has been omitted for clarity. Adapted from MaUcowski et al. [25]. (See insert for color representation of the figure.)... 

The [Co "(protoporphyrin IX dimethyl ester)(MeO)(MeOH)] complex is very suitable for the study of the nature of bonds of strongly bound entering amine ligands, which easily replace the weakly bonded outgoing methanol. Replacements of both ligands, MeO and MeOH, can be followed spectro-photometrically in methanol solvent using the stopped-flow technique. " Replacements of MeOH and MeO ligands proceed consecutively in this order (eqs. 8.5.1 and 8.5.2) ... 

Cytochrome P450 monooxygenases are characterized through the presence of the heme (protoporphyrin IX) prosthetic group (Scheme 10.1) that is coordinated to the enzyme through a conserved cysteine ligand. They have obtained their name from the signature absorption band with a maximum near 450 nm in the difference spectrum when incubated with CO. The absorption arises from the Soret Jilt transition of the ferrous protoporphyrin IX-CO complex. 

The NIS investigation of heme complexes includes various forms of porphyrins (deuteroporphyrin IX, mesoporphyrin IX, protoporphyrin IX, tetraphenylpor-phyrin, octaethylporphyrin, and picket fence porphyrin) and their nitrosyl (NO) and carbonyl (CO) derivatives, and they have been the subject of a review provided by Scheidt et al. [109]. 

Tin(IV)-protoporphyrin (254), Ga-deuteroporphyrin (255), and Co-mesoporphyrin (256) complexes are potent inhibitors of heme oxygenase. The Sn(IV) complex significantly inhibits bilirubin production... 

Figure 9-8. Pathway for metabolism of heme and excretion as bilirubin. Heme degradation begins with heme oxygenase, which catalyzes a complex set of reactions that simultaneously open the protoporphyrin ring structure and release iron in the ferric (Fe ) state. This is the only physiologic reaction that makes endogenous CO in the body a portion of the small amounts made is expired via the lungs. The structure of the main form of bilirubin is shown. Symbols for the side groups indicate M, methyl V, vinyl P, propyl. Formation of the diglucuronide is catalyzed by bilirubin uridine diphosphate (UDP) glucuronyltransferase. RE, reticuloendothelial.

Parallel studies were carried out cm the Co(ll)poiphyrin complexes91. We chose two porphyrin derivatives soluble in organic solvents protoporphyrin IX dimethyl-ester (PPME) 38, and tetraphenylporphyrin (TPP) 39. 

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