Heme Metabolism Flashcards
Hemoglobin, cytochromes, peroxidases, and catalse are categorized as what?
Hemoproteins
What has 4 linked pyrrole rings with a central Fe2+?
Porphyrin ring
What two substrates form delta-aminolevulinate?
Glycine and succinyl CoA
What is the enzyme that produces ALA?
ALA Synthase
What is the coenzyme in the formation of ALA?
Pyridoxal phosphate
What controls enzyme activity and transcription of delta-ALA gene?
The level of heme in the cell
What is formed from two molecules of ALA being condensed?
Porphobilinogen
What enzyme condenses two ALA molecules to form porphobilinogen?
ALA dehyrdatase
What is ALA dehydratase inhibited by?
Lead
How many molecules of glycine and succinyl CoA are required to produce 1 heme molecule?
8
Heme is formed from what, by insertion of Fe2+
Protoporphyrin IX
What enzyme inserts Fe2+ into protopophyrin forming heme?
Ferrochelatase
Defective enzymes have been found for most steps in heme synthesis, creating conditions known as what?
Porphyrias
What is the most common porphyrias?
Porphyria cutanea tarda
Most porphyrias are photosensitive except which two?
ALA dehyrdatase prophyria and acute intermitten porphyria
Heme synthesis requires what two types of reactions?
Decarboxylation and oxidation
Where are RBCs destroyed?
Mostly in the spleen, somewhat in the liver
Heme, in its first degradative step, is oxidized to what? (2)
Biliverdin and CO
Biliverdin is reduced to what?
Bilirubin
What transports bilirubin to the liver?
Serum albumin
What happens to bilirubin in the liver?
It is conjugated to glucuronate and secreted into the bile
Bilirubin diglucuronide is hydrolyzed to what? where does this happen?
Free bilirubin; intestines
What converts bilirubin into urobilinogens and stercobilins?
Bacteria
What happens to urobilinogens and stercobilins?
They are excreted into the urine and feces
What does icterus mean?
Yellowing of the skin
Accumulation of bilirubin in skin and mucous membranes is known as what?
Jaundice
Accumulation of bilirubin in nerve tissue is known as what?
Kernicterus
Which of the three types of jaundice comes from conditions that cause excessive levels of RBC destruction, overwhelming the heme degradation capacity?
Prehepatic (hemolytic)
Which of the three types of jaundice comes from conditions of the liver that interfere with bilirubin uptake or conjugation enzyme (bilirubin glucuronyl transferase)?
Hepatic (hepatocellular)
Which of the three types of jaundice comes from physical obstructions that prevent bile from reaching the intestinal tract?
Posthepatic (obstructive)
What is the protein that is produced in the liver and carries two Fe3+ in the circulation?
Transferrin
What is the protein that is produced in the liver, is used to store iron as a hydroxyphosphate, and binds over 2000 Fe3+’s
Ferritin
What is formed with high iron uptakes; consists of granules of protein, polysaccharide and Fe3+?
Hemosiderin (associated with excess Fe)
