Porphyrins

Porphyrins


Porphyrins

  • Porphyrins  are cyclic molecules  formed  by fusion of four pyrrole  rings linked  by  methenyl  bridges.
  • side  chains  may be  acetate (A), propinonate  (P), methyl  (M)  or vinyl  (V)  groups.
  • The technical name for 4 pyrroles connected together is a tetrapyrrole.
  • There  are  two  types  of porphyrins,  porphyrin  I  and  porphyrin  III.
  •  Heme is the most important porphyrin III.
  • Type  III  porphyrins  are far more abundant.
  • The  important  porphyrins are: 
  1. Uroporphyrins  (contain acetate  and  propionate as  substituent groups),
  2. coproporphyrizs  (contain  methyl  and  propionate  as  substituent  groups)
  3. protoporphyrin (contain  vinyl, methyl  and propionate  as  substituent groups).
  • Heme  is  protoporphyrin.
  • Uroporphyrin, the most water-soluble of the porphyrins, is excreted predominantly in urine, coproporphyrin in urine and bile, whereas protoporphyrin the least soluble, is excreted only in the bile
  • Reduced form  of porphyrins  is  called  porphyrinogens.
  • porphyrins are  coloured compounds and have luminous  property.
  • reduced porphyrins (porphyrinogens)  are  colourless  and  nonluminous.
  • In porphyrinogens Pyrrole  rings  are  joined  by methylene bridges (-CH2-), whereas in porphyrins Pyrole  rings  are joined  by  methenyl  bridges(-HC=).
  • All porphyrias are autosomal dominant except ALA dehydratase deficiency and Congenital Erythropoetic Porphyria, which are autosomal recessivee, and X-linked sideroblastic anemia, which is X-linked recessive in inheritance.
  • Photosensitivity manifest as fluid vesicle and bulla develop on sun exposed areas.
  • Hyperpigmentation and hypertrichosis especially on face in porphyria cutanea tarda and congenital erythropoetic porphyria

Exam Important

  • There  are  two  trPes  of porphyrins,  porphyrin  I  and  porphyrin  III.
  • Heme is the most important porphyrin III.
  • Type  III  porphyrins  are far more abundant.
  • Heme  is  protoporphyrin.
  • Uroporphyrin, the most water-soluble of the porphyrins, is excreted predominantly in urine, coproporphyrin in urine and bile, whereas protoporphyrin the least soluble, is excreted only in the bile
  • Reduced form  of porphyrins  is  called  porphyrinogens.
  • porphyrins are  coloured compounds and have luminous  property.
  • reduced porphyrins (porphyrinogens)  are  colourless  and  nonluminous.
  • In porphyrinogens Pyrrole  rings  are  joined  by methylene bridges (-CH2-), whereas in porphyrins Pyrole  rings  are joined  by  methenyl  bridges(-HC=)


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