Zn -protoporphyrin

Grandjean P, Lintrup J. 1978. Erythrocyte-Zn-protoporphyrin as an indicator of lead exposure. Scand J Clin Lab Invest 38 669-675. 

Artifical photosynthetic reaction centers have continued to peak the interest of scientists over the years and this year is no exception. One such catenane-type example contains a ruthenium /m(2,2 -bipyridine) center, as the sensitizer, which is linked with cycloW.v(paraquat-p-phcnylenc), as the acceptor, and covalently linked with a protoheme or Zn-protoporphyrin, as the donor, located in the myoglobin pocket <00JA241>. A related assembly and on a Au-particle has appeared which possesses a Ru(II)-rm(2,2 -bipyridine)-... 

Hamachi I,Takashima H,Tsukiji S, Shinakai S, Nagamune T, Ogoshi H. Electron transfer from Zn-protoporphyrin IX to ruthenium amine attached at His63 of reconstituted cytochrome b562- Chem Lett 1999 551-2. 

The spectrum of a typical metalloporphyrin, e. g. Zn protoporphyrin, is shown in Fig. 5. The intense (e 10s) band around 25 kK is known as the Soret or y-band, while the two weaker bands (e 104) are designated a- and / , the a-band lying at lower energy. Electron donor substituents... 

Figure 45. Reconstitution of apo-myoglobin with a Zn- protoporphyrin IX linked covalently to an electron acceptor (31 or 32) and vectorial photoinduced electron transfer in the assembly.

Figure 46. Interprotein photo-induced electron transfer in a system composed of positively charged cytochrome c and myoglobin reconstituted with Zn-protoporphyrin IX covalently bound to a negatively charged comb providing association of the proteins in the assembly.

Ferrochelatase (protoheme ferro-lyase) ° ° inserts Fe + into protoporphyrin IX to form heme. The enzyme is found firmly bound to the inner membrane of mitochondria of animal cells, chloroplasts of plants, and chromatophores of bacteria. While Fe " is apparently the only metallic ion ordinarily inserted into a porphyrin, the Zn + protoporphyrin chelate accumulates in substantial amounts in yeast, and Cu +-heme complexes are known (p. 843). Ferrochelatase, whose activity is stimulated by Ca +, appears to be inhibited by lead ions, a fact that may account for some of the acute toxicity of lead." " ... 

In studying ET between proteins, complications may arise because the systems exhibit more than one stable conformational state (66). In hemoglobin (Hb), for example, the U2P2 tetramer exists in two distinct states, T (deoxyhemoglobin) and R (oxyhemoglobin). Electron transfer between subunits in hemoglobin hybrids, [ai(Fe), P2(Zn)] and [ai(Zn), p2(Fe)], has been studied by Hoffman and co-workers (47, 66, 121, 151). The association of the Fe and Zn subunits has been extensively characterized (121) photogenerated Zn-protoporphyrin transfers an electron to a ferriheme acceptor, as outlined in Scheme V. 

The alteration of the enzymatic activity of ferrochelatase due to the inhibition of this enzyme by the effect of Pb produces an increase in the protoporphyrin IX concentration in erythrocytes. This increase of protoporphyrin IX produces and accumulation of Zn-protoporphyrin I due to the complexation formation of this porphyrin with Zn. ... 

The identification and quantification of high levels of porphyrins in erythrocytes, mainly protoporphyrin IX and its chelated form, Zn-protoporphyrin, are essentials in the diagnosis of Pb poisoning and in erythropoietic porphyrias (Meyer et al., 1980b). 

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]. 

Since 2 is produced inside the protein, a potential drawback of these nanosystems is that 2 can be quenched by the protein s aminoacids on its journey to the external medium. This was assessed by Lepeshkevich et al. in a very elegant piece of work, in which the heme in myoglobin was replaced by Zn-protoporphyrin IX (ZnPP) (Fig. IIB). They found that, on average, six out of ten 2 molecules succeeded in escaping from the protein matrix into the external medium. 

Using a typical poly (vinyl chloride) (PVC)-based membrane with different ionophores - Zn-bis(2,4,4-trimethylpen-tyl) dithiophosphinic acid complex [450], protoporphyrin IX dimethyl ester [451], porphyrin derivative [452] and hemato-porphyrin IX [453], tetra(2-aminophenyl) porphyrin [454], cryptands [455, 456], 12-crown-4 [457], benzo-substituted macro-cyclic diamide [458], 5,6,14,15-dibenzo-l, 4-dioxa-8,l 2, diazacyclopentadecane-5,14-diene [459], and (A-[(ethyl-l-pyrrolidinyl-2 -methyl) ] methoxy-2-sulfamoyl-5 -benza-mide [460] - the sensors for zinc ions were prepared and investigated. The armed macrocycle, 5,7,7,12,14,14-hexamethyl-1,4,8,11 -tetraazacyclo tetradeca-4,11 -diene dihydrogen perchlorate was used for the preparation of polystyrene-based Zn(II)-sensitive electrode [461]. 

Fig. 9. Proton NMR spectra at 220 Me of solutions in d5-pyridine of the Zn(II)-complexes with porphin, and the dimethylesters of mesoporphyrin IX, deuteropor-phyrin IX, and protoporphyrin IX. The resonance assignments were based on the relative resonance intensities and the observed fine-structure from spin-spin coupling they agree with previously published data by Caughey and Koski (17 a = ring methyls (for porphin protons at positions 1 to 8), b = mesoprotons, c and d = methylene protons of the propionates, e = methylesters, / and g = resonances of the substituents at positions 2 and 4. Three strong resonances between —7 and —9 ppm come from d5-pyridine, the line at ca. —4.9 ppm from HDO. T = 25 °C...

Enzymatic activity is dependent upon several variables, such as enzyme and substrate concentrations, pH, salt concentration of the buffer milieu, temperature and light. Many enzymes also possess non proteinaceous chemical portions termed prosthetic groups. Typical prosthetic groups are the iron protoporphyrin of peroxidase, and biotin of carboxy transferases. In addition, many enzymes require the presence of metal ions such as Mg++, Mn++, and Zn++, which function as electrophilic (electron attracting) agents. 

In iron deficiency anemia, Zn2+ may be used instead of iron by ferro-chelatase in the biosynthesis of heme. Red blood cell lysates in such instances contain increased quantities of Zn-hemoglobin. In addition, red cells from iron-deficient patients also contain increased amounts of protoporphyrin IX. Zinc-hemoglobin and protoporphyrin IX determinations are thus used in the diagnosis of iron deficiency anemia. 

In iron deficiency anemia, red blood cells contained increased quantities of Zn-hemoglobin and protoporphyrin IX. 

The product, Zn-mesoporphyrin, mesoporphyrin and Zn-deuteroporphyrin (internal standard) are separated on an ODS-Hypersil column (5 mm x 250 mm). The mobile phase was 88% (v/v) methanol in 1 M ammonium acetate, pH 5.16. Fluorescence detection was used, with excitation at 405 nm and emission at 574 nm. Protoporphyrin was also used as a substrate, in which case excitation and emission wavelengths were 410 and 590 nm, respectively. The amount of product formed was determined from calibration curves. 

The standard incubation mixture contained 100 fiL of 0.25 M Tris-HCl buffer (pH 7.4) containing 1.75 mM palmitic add and 1% (w/v) Tween-20 50 /x.L of enzyme preparation (about 0.5 mg protein), and 50 tL of 80 or 100 nM zinc acetate solution. After incubating 5 minutes at 37°C, the reaction was started by adding 50 / L of 100 /iM mesoporphyrin or protoporphyrin. The incubation was continued for 30 minutes at 37°C in the dark. The reaction was stopped by adding 1 mL of ice-cold methanol-DMSO (8 2, v/v) containing 13 nM Zn-deuteroporphyrin as internal standard. The mixture was cooled on ice and centrifuged before analysis of the supernate by HPLC. The... 

An alternative approach to the preparation of photoenzymes by the reconstitution of apo-proteins includes the application of metalloprotoporphyrins such as Zn(II)-protoporphyrin IX (Zn-P), which exhibits photophysical electron-transfer properties for the reconstitution of apo-proteins derived from hemoproteins. Func-... 

Finally, it is widely known that Pb impairs the formation of red blood cells. The mechanism involved in the impairment is that Pb inhibits both 5-aminolevulinic acid dehydratase (ALA-D) (Hernberg et al. 1970) and ferrochelatase (Tephly et al. 1978). These are two key enzymes involved in heme biosynthesis. ALA-D catalyzes the conversion of 5-aminolevulinic acid into porphobilinogen (PBG), whereas ferrochelatase is responsible for catalyzing the incorporation of Fe2+ into protoporphyrin IX to form heme (Figure 9.1). Lead inhibition of the two enzymes appears to be due to its interaction with Zn and Fe required in the process. 

FECH (also known as heme synthase) is an iron-sulfur protein located in the inner mitochondrial membrane. This enzyme inserts ferrous iron into protoporphyrin to form heme During this process, two hydrogens are displaced from the ring nitrogens. Other metals in the divalent state will also act as substrate, yielding the corresponding chelate (e.g., incorporation of Zn into protoporphyrin to yield zinc protoporphyrin). In iron-deficient states Zn successfully competes with Fe in developing red cells so that the concentration of zinc protoporphyrin in erythrocytes increases. Furthermore, other dicarboxylic porphyrins will also serve as substrates (e.g., mesoporphyrin). 

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