Porphyrin: Difference between revisions
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<Structure load='Heme3.Mol' size='500' frame='true' align='right' caption=' | <Structure load='Heme3.Mol' size='500' frame='true' align='right' caption='Porphyrins are not complexed with metal ions.' scene='Porphyrin/Initial/2' /> | ||
Porphyrins are a macrocyclic compounds containing four pyrole rings. Can you identify them in the scene to the right? The four pyrole rings are connected together by four <scene name='Porphyrin/Methenyl/1'>methenyl groups</scene>. Porphyrins are distinguished from each other by the substituents attached to the pyrole rings. Can you identify the pyrole substituents on this porphyrin (protoporphyrin IX)? They are <scene name='Porphyrin/Methyl_groups/1'>methyl</scene>, <scene name='Porphyrin/Vinyl_groups/1'>vinyl</scene> and <scene name='Porphyrin/Propioic_groups/1'>propioic acid</scene> groups. | Porphyrins are a macrocyclic compounds containing four pyrole rings. Can you identify them in the scene to the right? <scene name='Porphyrin/Initial/2'>(initial scene</scene>) The four pyrole rings are connected together by four <scene name='Porphyrin/Methenyl/1'>methenyl groups</scene>. Porphyrins are distinguished from each other by the substituents attached to the pyrole rings. Can you identify the pyrole substituents on this porphyrin (protoporphyrin IX)? They are <scene name='Porphyrin/Methyl_groups/1'>methyl</scene>, <scene name='Porphyrin/Vinyl_groups/1'>vinyl</scene> and <scene name='Porphyrin/Propioic_groups/1'>propioic acid</scene> groups. An important function of porphyrins is to form <scene name='Porphyrin/Heme/1'>hemes</scene> by complexing Fe<sup>2+</sup> or Fe<sup>3+</sup> with the lone pairs of electrons on the four nitrogens. Heme displayed as | ||
<scene name='Porphyrin/Heme_spacefill/1'>spacefill</scene>. Since Fe<sup>2+</sup> and Fe<sup>3+</sup> prefer to complex with six ligands, there are two positions open for nucleophilic groups to bond whenever the heme associates with a protein. Both of these groups may be residues of a protein, or one of them may be a small substrate molecule. In one of these two ways the heme becomes covalently connected to the protein, and therefore can be called a [[prosthetic group]]. Residues that are commonly found as the fifth or sixth ligands are His, Cys and Met. Examples of the fifth ligand being His and the sixth ligand being a small molecule are [[oxymyoglobin]] and [[hemoglobin|oxyhemoglobin]]. | |||