Showing papers on "Protoporphyrin IX published in 1976"

Equilibrium and kinetic studies of the aggregation of porphyrins in aqueous solution

Abstract: An investigation of the behavior of protoporphyrin IX, deuteroporphyrin IX, haematoporphyrin IX and coproporphyrin III in aqueous solution revealed extensive and complex aggregation processes Protoporphyrin appears to be highly aggregated under all conditions studied At concentrations below 4 muM, aggregation of deutero-, haemato- and coproporphyrin is probably restricted to dimerization At approx 4muM each of these three porphyrins exhibits sharp changes in spectra consistent with a "micellization" process to form large aggregates of unknown size This critical concentration increases with increasing temperature and pH, but is not very sensitive to variation in ionic strength Temperature-jump kinetic studies on deuteroporphyrin also imply an initial dimerization process, the rate constants for which are comparable with those for various synthetic porphyrins, followed by a further extensive aggragation The ability of a particular porphyrin to dimerize appears to parallel that of the corresponding iron(III) complexes (ferrihaems), although it is thought that ferrihaems do not exhibit further aggregation under these conditions

Biosynthesis of protoporphyrin-IX from coproporphyrinogen-III

Abstract: By use of tritium labelled substrates, and h.p.l.c., it is shown that protoporphyrin-IX (1d) is formed from coproporphyrinogen-III (2a)via a specific pathway involving harderoporphyrinogen (2b) rather than its isomer (2c).

Porphyrin-sensitized photooxidation of horseradish apoperoxidase

Abstract: Horseradish apoperoxidase (apoHRP) was reconstituted with various porphyrin derivatives, e.g., ferric, cupric, manganese, and zinc protoporphyrin IX, metal-free protoporphyrin IX, hematoporphyrin IX and deuteroporphyrin IX. The visible absorption spectra of these porphyrin-apoHRP complexes were examined. The time required for maximum development of the new Soret peak after reconstitution was used to measure the rate of porphyrin-apoHRP reconstitution. All of the four metal-protoporphyrins reconstituted with apoHRP at the same rate as metal-free protoporphyrin IX, whereas, for the metal-free porphyrins, the rates of reconstitution were in the order of deuteroporphyrin IX > hematoporphyrin IX > protoporphyrin IX. The porphyrins on the reconstituted porphyrin-apoHRP complexes were used as localized photosensitizers for photodynamic studies. No amino acid residues were oxidized on illumination of the ferric, cupric and manganese protoporphyrin IX-apoHRP complexes due to the paramagnetic properties of these metal ions. With diamagnetic zinc ion, two histidine and one methionine residues were oxidized, which was the same as in the protoporphyrin IX- and hematoporphyrin IX-apoHRP complexes. However, only one histidine was destroyed on illumination of the deuteroporphyrin IX-apoHRP complex. The results confirmed the resistance of horseradish peroxidase to photodynamic action and suggested the involvement of at least one histidine residue in the heme environment ofmore » horseradish peroxidase.« less

The binding and transport of heme by hemopexin.

Abstract: Hemopexin binds proto-, meso-, or deutero-ferriheme with high affinity, forming an equimolar, low-spin complex. The ferroheme-hemopexin complex, which coordinates with CO and readily autoxidizes, is also low-spin. Formation of the ferriheme-hemopexin complex requires essential histidine and tryptophan residues and induces changes in the protein's tertiary structure. These changes may be important for the uptake of the heme-hemopexin complex by hepatocytes. Hemopexin also binds other porphyrins including protoporphyrin IX, and uro- and coproporphyrins I and III in a 1:1 molar ratio, but they are readily displaced by heme and do not produce discernable changes in the protein's conformation. In preliminary experiments, a selective interaction in vitro between heme-hemopexin and isolated rat hepatocytes has been demonstrated. This information is used as the basis for proposed models of the heme-binding site of hemopexin and of the interaction of heme-hemopexin with the parenchymal cells of the liver.

Chlorophyll $\alpha$ Biosynthesis [and Discussion]

Abstract: Protoporphyrin IX is believed to be an intermediate common to both haem and chlorophyll biosynthesis. The pathway specific to chlorophyll starts with magnesium protoporphyrin and its monomethyl ester. Two routes have been proposed for conversion of the latter compound to protochlorophyllide: A, formation of the isocyclic ring followed by reduction of the 4-vinyl group, or B, reduction of the 4-vinyl group followed by formation of the isocyclic ring. Membranes prepared from isolated barley etioplasts are found to convert magnesium 2,4-divinylphaeoporphyrin a $_5$ monomethyl ester to chlorophyllide a at a rate equal to that of chlorophyll synthesis in intact leaves: this result supports route A. NADPH is necessary to maintain the two successive reductive steps: reduction of the 4-vinyl group and then the photoreduction of ring IV to yield chlorophyllide. The prohaem content of etiolated leaves does not increase during the phase of active chlorophyll synthesis although evidence is presented that suggests that the ALA synthesis reaction that regulates chlorophyll synthesis is common to both pathways. This and other regulatory aspects are discussed.

Notizen: Binding and Kinetics of 1-Methylimidazol on Fe(III)-Protoporphyrin(IX)dimethylester and Fe(III)-Tetraphenylporphyrin in Chloroform

Abstract: Nuclear magnetic line widths data have been used to determine the rate of solvent exchange between the coordination sphere of Fe(III)-protoporphyrin(IX)dimethylester or Fe(III)-tetraphenylporphyrin and the bulk phase of 1-methylimidazol/chloroform. At temperatures below 322 K both porphyrins are in the low-spin state and separate PMR absorption caused by the methyl protons of two 1-methylimidazol molecules complexed in fifth and sixth position of ferri-porphyrins is detected. At T ≳ 320 K an accelerated exchange of these ligands was observed and the underlying kinetic parameters have been extracted. It was found that this exchange takes place when the paramagnetic species is in its low-spin state. For 240 K ≲ T ≲ 290 K dynamic line broadening of bulk phase 1-methylimidazol indicates occurrence of chemical exchange attributed to 1-methylimidazol interacting with ferri-porphyrin in addition to the strongly bound axial ligands.