Heme oxygenase in Chlamydomonas reinhardtii

  Heme oxygenase catalzyes a multistep reaction that breaks open heme to release Fe(III) and a-biliverdin IX.

View the complete reaction

In mammalian cells Heme oxygenase (HO) has two basic functions, first it recycles iron supplies within the cell to maintain homeostasis, second a-biliverdin and biliruben (its reduced form), are powerful antioxidants believed to aid in the prevention of oxidative cell damage. In cyanobacteria and some algae, HO functions to provide cofactors for the photosynthetic apparatus. Besides regulating iron homeostatis, HO makes a-biliverdin which is a precursor to both phycobilins and phytochromobilins. In red algae and cyanobacteria, phycobilins are precursors to the chromophores found in phycobiliproteins which act as light harvesting molecules. In higher plants phytochromobilins are precursors to the chromophores of phytochromes which function in light signalling. The plant HO reaction uses ferrodoxin to supply reducing equivalents in contrast to NADPH for animal HO. The following is the assembled HO sequence for C. reinhardtii.

-24                                       GCACGAGGCACTCGTTCGATAACA
+1    ATGCTTCTGTCCTCTCGATCCACCGCCTCGGTCCGTGCCAGCGGTCGCGCTGCACCTGCG
      M  L  L  S  S  R  S  T  A  S  V  R  A  S  G  R  A  A  P  A
+61   CCTCGCCGCGTGGTGCGTGTCCTGGCCCACGGTCATGGTCACGGAGGTGGCCATGGTCAC
      P  R  R  V  V  R  V  L  A  H  G  H  G  H  G  G  G  H  G  H
+121  GGCCATGGCTCGAGTGGCACGGCGGTGCTGACGGAGAAGGACAAGGGCTTTATTGCTGAG
      G  H  G  S  S  G  T  A  V  L  T  E  K  D  K  G  F  I  A  E
+181  ATGCGCAAGGTGGCAATGAAGCTGCATACGAAGGACCAGGCGCCTAAGGAGGGCGAGAAG
      M  R  K  V  A  M  K  L  H  T  K  D  Q  A  P  K  E  G  E  K
+241  GAGGCCCCCAAGCAAGGCCCGTGGACGCCCACTCGCCCGGGTTACCTGCGCTTCCTGGTT
      E  A  P  K  Q  G  P  W  T  P  T  R  P  G  Y  L  R  F  L  V
+301  GAGTCGAAGGAGGTCTTTGATACTTTCGAGCGCCTTGTCAACTCCAGCGACGCCTACAAG
      E  S  K  E  V  F  D  T  F  E  R  L  V  N  S  S  D  A  Y  K
+361  GCGCTGCGCAACACGGGTCTGGAGCGCGGGCCAGGCCTGGCTGCCGACATTGCCTGGATG
      A  L  R  N  T  G  L  E  R  G  P  G  L  A  A  D  I  A  W  M 
+421  GAGCAGTCCTTCCAGCTGGCGCCCCCGGACATGAAGCCGGACGGCGCGGCCGCCACCTAC
      E  Q  S  F  Q  L  A  P  P  D  M  K  P  D  G  A  A  A  T  Y
+481  GTGGCCTTTCTGGAGAAGCTCGCCAAGACCGACCCGCCCGCCTTCATCTGCCACTACTAC
      V  A  F  L  E  K  L  A  K  T  D  P  P  A  F  I  C  H  Y  Y
+541  AACTTCTATTTCGCACACACCGCCGGCGGCCGCATGATCGGCAACAAGGTGTCCAGCATG
      N  F  Y  F  A  H  T  A  G  G  R  M  I  G  N  K  V  S  S  M 
+601  CTGCTGGACGGCCAGACCCTGGAGTTCTACAAGTGGCAGGGCGACGTAAACGAGCACCTG
      L  L  D  G  Q  T  L  E  F  Y  K  W  Q  G  D  V  N  E  H  L
+661  GAGGGCGTGCGCAAGTCCATCAACGTGATGGCCGAGGGCTGGACCCCGGCGGAGAAGGAG
      E  G  V  R  K  S  I  N  V  M  A  E  G  W  T  P  A  E  K  E
+721  CACTGCCTGGCGGAGACGAGTCCAGCTTCAAGTACAGCGGCCAGATCCTGCGCGCTATCC
      H  C  L  A  E  T  S  P  A  S  S  T  A  A  R  S  C  A  L  S
+781  CCAAGGCATAAAGCAAAAGGCGGTAGCAGCAGCCTCTCAGGATGCGTTGGGCGGCAGAAA
      P  R  H  K  A  K  G  G  S  S  S  L  S  G  C  V  G  R  Q  K
+841  CTGCATGAATGTGCGAGTGGGGAAGAAGGAAAGGAAGTCGCCGGCAGTTGGAAACAGGCG
      L  H  E  C  A  S  G  E  E  G  K  E  V  A  G  S  W  K  Q  A
+901  GGCGGGCTGGCGGGCATATGATTGAGGCCTGGGCAAGGCCACGCGGGTGCTTGCCGAAAG
      G  G  L  A  G  I  *
+961  GGGCAATAGCATGCTGTTGGGCGCCCGGGCGCCTGCGGGCAACAGTGCCCCTCGTGGTGG
+1021 AGGACCCGGAAAAGGCGGTTGGCCTGCCCTGGAGGTGGTAGGCCACACAACGGCGGTGTC
+1081 GGAGGGTGTAGCATCCAGTAGGGCGCAGGCGGCTCGGGCATGCCTGGGTGTGGCTGTGTG
+1141 GGCTGGGCCGTATGCGGAAAAGGAGCGTTAAGGTATGGTGGTGACTCGGTTCAATGGCTA
+1201 TCGGACGGCATTATGGATGCATTGCATTCCTACCGGTGTTGTGCGCCTGATTTGTTGGAT
+1261 GGTCCCGGCTGGGGCCCGAGCGTGTGCTTAGGCGCTCCAACTGGTGGTGTTTTGTGTGTA
+1321 AGACTGTGCTTCGGTGACAGGTGCCCTATGGCAAACGGTTATGAAAGTTTCTGCAGGTGC
+1381 AAGATAAATGCAGCGATATGAGTTAAAGGGTTGGAATGACGGTGAGCGCGCCTTGAGTGT
+1441 AAAAAA