BMB401 Exam 2 Notes - Lecture 11: Heme: Fe- Protoporphyrin...

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Lecture 11: Heme: Fe- Protoporphyrin IX Rx n Type Reactants Products Enzyme Place 1 Condensation Succinyl CoA + Glycine δ - ALA δ ALA synthase Mt Matrix Rate limiting step 2 Dehydration synthesis 8 δ -ALA 4 Porphobilino gen 3 Condensation 4 Porphobilinogen Linear tetrapyrrole Porphobilinogen Deaminase 4 Cyclization Linear tetrapyrrole UroIII UroIII synthase + cosynthase δ - ALA synthase - short lived protein, rapidly degraded within 30 min. of synthesis. Unless continued transcription/ translation concentrations will decrease Transport into mitochondrion blocked by high heme concentration Heme negative feedback
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Rate limiting step = reaction 1: δ ALA synthase… Takes longest time Dictates pathway speed Most regulated step in pathway Linear tetrapyrrole Prophobilinogen Deaminase - link 4 PB molecules head to tail to form a linear tetrapyrrole, releasing 1 NH4+ ion for each methylene bridge made. : 2 substituents linked to ring. . Cosynthase: helps to establish asymmetry of UroIII in reaction 4 cyclization reaction. . Flips one of pyrolles prior to cyclization of ring- AP, AP, AP, PA Uroporphyrinogen III - asymmetric ring, made from cyclized linear tetrapyrrole. Uroporphyrinogen I - symmetric ring (metabolic dead end, can’t be used further in any synthesis) Without cosynthase UroI and Uro III are made Protoporphyrin IX : asymmetric ring, iron chelated in center Ferrochelatase: chelates iron to form heme Ferritin- intracellular iron storage Made of 24 subunits in a ball like structure with a hollow core, in which iron is localized Localization of iron in ferritin, allows iron to be kept in soluble/ easily accessible form
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Transferrin: -Carries iron in the blood/ extracellular space; -Can only carry 2 Fe3+ ions After acidification, transferrin transfers iron to ferritin, and then ferritin is recycled by transport thru exocytic pathway out of cell Transferrin receptor - endocytost into cell in an endocytic vesicle. . this endocytic vesicle goes thru endocytic pathway and becomes acidified Porphyrias - problems with heme synthetic pathway. . 2 types caused by deficiency in particular enzyme 1. Acute intermittent porphyria- deficiency in reaction 3 enzyme porphobilinogen deaminase 2. Congenital erythropoietic porphyria- deficiency in reaction 4 cosynthase uroI a symmetric ring is formed in addition to UroIII Spleen - primary site of RBC scavenging 120 days - RBC avg. lifespan Globin chains - Hb protein components; hydrolyzed to individual AAs 1- stercobilin - excreted in feces Orange- red color Further breakdown product 1- urobilin - excreted in urine …. . (product is reabsorbed, transported to kidneys, then excreted) Orange yellow colow Heme oxygenase - break α methane bridge in protoporphyrin release ferric iron;
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Products of reaction= Biliverdin, CO, H2O, NADP+ Biliverdin Reductase - reduce biliverdin bilirubin Reduction of central methen bridge
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This note was uploaded on 10/18/2011 for the course BMB 401 taught by Professor Kaguni during the Fall '08 term at Michigan State University.

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BMB401 Exam 2 Notes - Lecture 11: Heme: Fe- Protoporphyrin...

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