Protoporphyrins

About: Protoporphyrins is a research topic. Over the lifetime, 145 publications have been published within this topic receiving 3486 citations.

In situ STM and AFM study of protoporphyrin and iron(III) and zinc(II) protoporphyrins adsorbed on graphite in aqueous solutions

Abstract: Iron(III) protoporphyrin(IX), zinc(II) protoporphyrin(IX), and protoporphyrin(IX) have been studied on the graphite basal plane in aqueous solutions with both scanning tunneling (STM) and atomic force (AFM) microscopies. Real-time images directly show that the molecules adsorb onto the electrode and condense into monolayer films starting from small islands. In the monolayer films, all three molecules lie flat on the surface and form identical two-dimensional lattices with a = 13.4 ± 0.2 A, b = 12.2 ± 02 A, and γ = 68 ± 2°. The corresponding molecular packing density is 1.1 x 10 -10 mol/cm 2 , which is in excellent agreement with the value determined from cyclic voltammograms. Although the three molecules are nearly identical in their geometrical structures, their internal structures revealed by STM are significantly different. After the monolayer is completed, iron(III) protoporphyrin(IX) forms aggregates with a thickness of ∼8.5 A, while zinc(II) protoporphyrin(IX) and protoporphyrin(IX) do not.

Studies on the biosynthesis of porphyrin and bacteriochlorophyll by Rhodopseudomonas spheroides. 4. S-Adenosylmethionine–magnesium protoporphyrin methyltransferase

Abstract: Gibson, Neuberger & Tait (1962b) have shown that ethionine inhibits the biosynthesis of bacteriochlorophyll and stimulates the excretion of coproporphyrin by illuminated suspensions of Rhodopseudomonas spheroides, and that this effect can be reversed by methionine. It was suggested that methionine might be concerned in a specific manner in the formation of bacteriochlorophyll, and evidence was presented to show that the methyl group of methionine is a direct precursor of the methyl ester group of bacteriochlorophyll. Tait & Gibson (1961) reported that chromatophores from Rps. spheroides catalyse the transfer of the methyl group of S-adenosylmethionine to magnesium protoporphyrin to form a compound that was tentatively identified as magnesium protoporphyrin monomethyl ester. The present paper describes the further characterization of the enzyme, S-adenosylmethionine-magnesium protoporphyrin methyltransferase, and the identification of the product formed.

The porphyrin requirements of haemophilus influenzae and some functions of the vinyl and propionic acid side chains of heme.

Abstract: 1. Iron protoporphyrin IX was required for the growth of H. influenzae. It could be replaced by protoporphyrin IX. When grown on protoporphyrin evidence was obtained for the presence of Fe porphyrin in the organism. It was concluded that the organism could insert iron into the protoporphyrin ring. 2. In the smooth strains, other porphyrins containing no iron such as deutero-, hemato-, meso-, and coproporphyrins could not replace protoporphyrin for growth. Since protoporphyrin has two vinyl groups which other porphyrins lack, it was concluded that the two vinyl groups were essential for growth. 3. When porphyrins lacking vinyl groups were converted chemically into iron porphyrins and then supplied to the organisms it was found that these iron porphyrins supported growth. It was concluded that the "smooth" organisms were able to insert iron only into the porphyrin containing the vinyl groups; i.e., protoporphyrin. One function of the vinyl groups then was to permit iron to be inserted biologically into the porphyrin ring. 4. An anomalous behavior in the rough Turner strain was observed and discussed. This organism was able to insert iron into mesoporphyrin at low concentrations but was inhibited by this compound at higher concentrations. In all other reactions with the porphyrins this rough strain behaved in the same was as did the smooth strains. 5. All strains which were grown on iron porphyrins lacking vinyl groups could not reduce nitrate to nitrite. When grown on protoporphyrin or Fe protoporphyrin reduction of nitrate occurred. It was concluded that the nitrate-reducing mechanism required the presence of the vinyl groups either for its formation or function. 6. The porphyrins lacking iron and lacking vinyl groups inhibited the growth of H. influenzae on Fe protoporphyrin. The inhibition between a porphyrin and Fe protoporphyrin was a competitive one. It was suggested that the porphyrin inhibited the growth-promoting properties of Fe protoporphyrin by attaching on to a particular apoprotein, thus preventing the formation of a heme catalyst. Likewise, competition between two growth-promoting Fe porphyrins for apoenzymes could be shown to occur. 7. Protoporphyrin and Fe protoporphyrin supported growth. When their propionic acid side chains were esterified they no longer supported growth. It was suggested that the esterified carboxyl groups could not attach to the specific apoproteins to form the heme enzymes and so could not act to support growth. For the same reason the inhibitory action of porphyrins lacking vinyl groups could be prevented by esterifying their propionic acid groups.