Porphyrin Rings

1
Porphyrin Rings

• Produced mainly in
• Liver
• Erythrocyte producing cells of bone marrow
• Not mature erythrocytes (lack of mitochondria)
• Initial step and last three steps are in the
  mitochondria
• Glycine and Succinyl CoA are precursors
• Hemin is feedback inhibitor of ?-aminolevulinic
  dehydrase (ALA) (?-delta)
• Lead is inhibitor of this pathway

2
Porphyrin Uses

• Cytochromes
• P450, b5, ETS
• Hemoglobin

3
Porphyrin Pathway

• Begins in Mitochondria
• Vitamin necessary in first enzyme
• reaction
• Pyridoxal Phosphate
• Porphobilinogen is first molecule
• in cytosol

4
Porphyrins Cont

• Addition of ferrous iron in
• mitochondria
• ferrochelatase

5
Porphyrias

• Usually hereditary porphyrin production defects
• General Classification
• Erythropoietic (defect in RBCs)
• Hepatic (Defect in liver)
• Usually autosomal dominant
• Covered in genetics

6
Heme Degradation

• First product is biliverdin (open ring)
• Heme oxygenase
• Biliverdin plus CO yields bilirubin
• Biliverdin reductase
• NADP
• Bilirubin
• Gut (microbial enzymes act on bilirubin)
• Produce Urobilinogen
• Absorbed and carried to liver to produce Urobilin
• Yellow color
• Large intestine further microbial enzymes produce
  Stercobilin
• Characteristic brown color
• Liver
• Conjugation with 2 moles of glucuronic acid
• Glucuronyl bilirubin transferase
• Forms bilirubin diglucuronide (polar and soluble)
• detox

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Porphyrin Ring Breakdown

8
Jaundice

• Hemolytic
• Response to sickle cell anemia
• Glycolytic enzyme deficiencies
• Erythroblastosis foetalis
• Obstructive
• Hepatic tumor
• Pale stools
• GI pain, nausea
• Hepatocellular
• Liver damage
• Cirrhosis, hepatitis
• Urine dark, stools pale (liver regurgitates
  conjugated bilirubin into blood and then into
  urine)
• Elevated AST (SGOT) and ALT (SGPT)

9
Hemoglobin

• Porphyrin ring
• Iron
• Oxygen Binding
• Two alpha chains and two beta chains
• ?1?2?1?2
• Thalassemias

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Genetics of Hemoglobin

• ?1?2
• Chromosome 16
• Diploid designation ?1?2/?1?2
• Produced in utero
• ?1?2
• Chromosome 11
• Produced postpartum only
• Alpha-like chains (?)
• pre- post-natal
• ? (zeta)
• Beta-like chains (?)
• Essentially post-natal
• ??? (sigma, epsilon, gamma)

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Hemoglobin Oxygen Release

• High acidity causes hemoglobin to release oxygen
• Erythrocytes passing through tissue that are
  producing acids-lactic acid
• Handoff to myoglobin
• Called Bohr effect (Christian Bohr-Physiologist)
• Named after father of noted physicist Niels Bohr
• 2,3-bisphosphoglycerate promotes release of
  oxygen by hemoglobin

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Representation of pH and Oxygen Binding

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Cooperative Oxygen Binding

• Myoglobin-rectangular hyperbola
• Hemoglobin-sigmoidal
• Partial pressure
• Saturation

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Structure of Hemoglobin

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Carbon Dioxide Hb

• Isohydric Transport of CO2
• Gas exchange without pH change
• Carbonic anhydrase (Zn-containing)

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Another Mechanism of CO2 Transport

• Direct reaction of carbon dioxide to produce
  carbaminohemoglobin

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Genetics Overview

• ?-psi pseudo-genes
• Mutations (mutated) such that they do not produce
  a functional protein
• ?-zeta

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Hemoglobinopathies

• Very common
• AR-Sickle Cell Anemia
• HbA vs HbS (?6 Glu?Val)
• Life long hemolytic anemia

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Hemoglobinopathies-Cont

• Thalassemias (thalassa-seamany cases around
  Mediterranian Sea)
• ? ?0 (some production vs. none)
• ? ?0(some production vs. none)
• Alpha thalassemias affect fetal and postpartum
  hemoglobin
• Beta thalassemias affect only postpartum

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Thalassemias-Cont

• Alpha thalassemia usually more severe
• Thalassemia major
• Variety of deletions (usually)
• Beta thalassemia usually less severe
• Thalassemia minor
• Usually single nucleotide substitutions

21
Iron

• Association with copper
• Absorption from lumen in intestine
• Ceruloplasmin
• Cupric to cuprous, ferrous to ferric
• Vitamin C
• Wilsons disease
• 1100,000
• Lack of copper transport proteins

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Iron Contained inSome Examples

• Hemoglobin, myoglobin
• NO binding, guanylate cyclase
• ETS hemes
• Cytochrome b5 in desaturation
• Iron-sulfur (Complex I, aconitase, xanthine
  oxidase, ferrochelatase (heme synth.)
• Phenylalaine hydroxylase, tyrosine hydroxylase,
  dioxygenases
• Etc.

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Proteins and Iron

• Iron binding proteins
• Transferrin (Fe3), Lactoferrin (Fe3), Ferritin
  (Fe3), Hemosiderin (Fe3)
• Proteins that use iron as substrate
• Ferroxidase (Fe2/Fe3)-adrenals, Ferrochelatase
  (Fe2)-porphyrins
• Protein that uses heme as substrate
• Heme oxygenase (biliverdin)

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Transferrin

• Plasma protein
• Glycoprotein synthesized by liver
• Single polypeptide (700 AAs)
• High affinity for ferric iron
• No affinity for ferrous iron
• Serum levels about 30umol/L
• Serum has excess iron binding capacity

25
Transferrin Cont

• Transferrin production increased during
• Iron deficiency
• Pregnancy (high estrogen levels)
• Women taking oral contraceptives
• Transferrin production decreased
• Excess iron
• Infection
• Inflammation
• Neoplasia
• Protein catabolic state
• Transferred to recipient cells by-
• Transferrin-binding Receptors

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Ferritin

• Store iron in ferrous non-toxic state
• Relatively short term storage
• Handoff to/from transferrin
• Handoff to/from hemosiderin
• Mainly intracellular
• Not usually in the serum unless iron storage
  saturation

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Other Transport Proteins

• Exist during high iron overload, ineffective
  erythropoiesis (hemes/hemoglobin in serum),
  hemolytic anemia, etc.
• Examples
• Haptoglobin
• Bind free (serum) oxyhemoglobin dimers
• Brought into hepatocytes by receptor mediated
  endocytosis
• Hemopexin and albumen bind free hemes
• Lactoferrin (neutrophils, secretory epithelial
  secretions (milk)

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Hemosiderin

• Long term storage
• Handoff to/from ferritin
• Exist in times of iron overload
• Probably a form of iron-ferritin complexes in a
  type of micelle formation in tissues

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Iron in Foods

30
Hypochromic Anemia

• Pale RBCs due to low levels of hemoglobin

31
Hemochromatosis

• Excess iron (free iron due to saturation of
  tranferrin)
• Arthritis, liver cancer, coronary occlusions
• Early diagnosis and treatment
• AR inheritance with gene on chromosome 6
• Treatment
• Venesection (removal of blood)
• Removal of 500ml of blood over specified
  frequency and period of time to lower iron
  reserves
• High frequency is 500ml per week over 1-2 year
  period of time
• Chelation

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Assessment of Iron

• Serum Ferritin Concentration
• Quantitative relationship to iron stores
• 20-200ng/mL
• Rememberferritin is usually tissue bound
• Note Some research has shown a relationship
  between excess iron, and heart disease and cancer
• Supplement only when deficient

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Copper in Enzymes