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MBC - Lecture 44

Heme Biosynthesis (Douglas)

Lecture 44 Heme Biosynthesis
___ is the most common porphyrin in the body. Heme
Heme is complexed with ___, ___, and ___. hemoglobin, myoglobin, and cytochromes
Heme transports ___. oxygen
Heme is degraded and excreted in the gut and urine as a conjugate of ___. bilirubin
Glycine + Succinyl-CoA → ___ 5-aminolevulinate (5-ALA)/ δ -aminolevulinate
5-ALA goes through 7 enzymatic steps to produce ___. heme
δ- aminolevulinate synthase (ALAS) contains ___. pyridoxal phosphate (PLP)
Lead inactivates the following enzymes: δ-aminolevulinic acid dehyrdatase, protoporphyinogen oxidase, and ferrochelatase
Uroporphyrinogen decarboxylase acts on side chains of ___. uroporphyinogen
Deficiency of uroporphyrinogen decarboxylase leads to accumulation of ___. uroporphyrinogen III
___ inhibits uroporphyrinogen decarboxylase. Iron salts
Poryphria Cutenea Tarda Most common porphyria, light sensitivity, recessive allele leading to 50% reduction of uroporphyrinogen decarboxylase activity with normal hepatic heme production, makes carrier sensitive to alcohol
Heme biosynthesis begins and ends in the ___. mitochondria
Aminolevulinate Synthase (ALAS) Catalyzes formation of 5-aminolevulinate (ALA) in the mitochondria from glycine and succinyl-CoA
Aminolevulinate Dehydratase (ALAD) Catalyzes formation of porphobilinogen (PBG) in the cytoplasm from ALA (aka porphobilinogen synthase)
Ferrochelatase Catalyzes formation of heme in the mitochondria by addition of Fe2+ to protoporphyrin
Under conditions of low iron availability, ___ can be inserted, resulting in a fluorescent molecule. zinc
___ is a negative feedback inhibitor of 5-ALAS. Heme
3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) inhibits ___. ferrochelatase
Porphyria Partial interruption in heme synthesis leading to excess porphyrin precursors in the liver
___ and ___ are neurotoxins, measurable in urine. ALA and porphobilinogen
Symptoms of porphyria include: abdominal pain, peripheral neuropathies, respiratory paralysis, and acute psychotic episodes
Porphyria are often ___, but can be triggered by fasting, dieting, or a chemical/hormone/drug. asymptomatic
Heme is degraded to non-soluble ___. bilirubin
Heme is cleaved by ___ to form biliverdin. heme oxygenase
Biliverdin is reduced by ___ to form bilirubin. biliverdin reductase
Bilirubin is transported to the __ by conjugation with ___. liver, albumin
Conjugation of bilirubin and ___, making it soluble for excretion in bile. glucuronic acid
Glucuronyl Bilirubin Transferase Catalyzes conjugation of bilirubin with glucuronic acid to form bilirubin diglucuronide
Bilirubin diglucuronide is released to the intestine and degraded to ___. urobilinogen
75% of bilirubin is from ___. red blood cells (250-350 mg/day)
Majority is excreted in feces as ___. stercobilin (brown color)
Normal bilirubin levels are <___ micromoles per liter. <17
Jaundice is clinically obvious when bilirubin levels are >___ micromoles per liter. >50
Pre-Hepatic Jaundice Increased bilirubin production by RBC breakage, blood extravasation, sickle cell anemia
Intrahepatic Jaundice Inability for liver to uptake, conjugate, or secrete bilirubin
Post-Hepatic Jaundice Obstruction of biliary excretion
Hepatic Failure Acetaminophen toxicity, 70 micromolar bilirubin
Neonatal Jaundice Common 48 hours after birth, after 10 days is abnormal, 150 micromolar bilirubin
Obstructive Liver Disease 230 micromolar bilirubin
___ measured in blood as markers for liver function/damage. Transaminases
Created by: emyang