Catabolism of carbon skeleton of amino acids

Catabolism of carbon skeleton of amino acids


Introduction

The  catabolism  of amino  acids  has two  parts

  1. Removal  of  amino  group  to  form ammonia,  which later  is  disposed after conversion  into  urea.
  2. Breakdown  of  the  remaining  carbon  skeletal,  which  remains  after  removal  of  amino group.

The carbon skeletons  of amino  acids is  degraded  into  seven  products: 

(i)  Pyruvate, (ii)  Acetyl-CoA,  (iii)  Acetoacetyl-CoA, (iv)  α-ketoglutarate,  (v)  Succinyl-CoA, (vi) Fumarate  and (vi)  Oxaloacetate.

  • All the products enter the citric acid cycle and are either involved in gluconeogenesis or in ketogenesis or either oxidized to CO2 and H2O with production of energy.
  • Amino acids  that  are  degraded  only  in  acetyl-CoA  or aceto-acetyl  CoA give rise  to  ketone  bodies,eg: Ieucine  and  lysine  are  ketogenic  amino acids.
  • Amino  acids  that  are converted  to  pynrvate,  α-ketoglutarate,  succinyl-CoA,  fumarate  or oxaloacetate,  are glucogenic  amino  acids,eg: alanine, glycine, serine
  • Amino acid which involves both gluconeogenesis  and ketogenesis are: isoleucine,  phenylalanine tryptophan  and  tyrosine.

For example: Enzymes involved in catabolism of Tyrosine:

  1. Tyrosine Transaminase: PLP  is  the  coenzyme  for  this  reaction, Deficiency causes Tyrosinemia type – II (Richer-Hanhart syndrome)
  2. pHydroxyphenylpyruvate Hydroxylase: Dioxygenase, Cofactor  is  Copper, Ascorbic  Acid  is needed for reaction.
  3. Homogentisate  Oxidase: Contains  Iron  at the  active  site.
  4. Maleyl acetoacetate  Cis-trans lsomerase: Need  Glutathione  (GSH)  as cofactor
  5. Fumaryl  Acetoacetate Hydrolase: defeciency causes Tyrosinemia type-I (tyrosinosis/hepatorenal syndrome)
  6. Products from  Tyrosine: Melanin, Catecholamines, Thyroxine, Norepinephrine, Dopamine.

Exam Important

  • Amino acids  that  are  degraded  only  in  acetyl-CoA  or aceto-acetyl  CoA give rise  to  ketone  bodies,eg: Ieucine  and  lysine  are  ketogenic  amino acids.
  • Amino  acids  that  are converted  to  pynrvate,  α-ketoglutarate,  succinyl-CoA,  fumarate  or oxaloacetate,  are glucogenic  amino  acids,eg: alanine, glycine, serine
  • Amino acid which involves both gluconeogenesis  and ketogenesis are: isoleucine,  phenylalanine tryptophan  and  tyrosine.
  • Enzymes involved in catabolism of Tyrosine:
  • Products from  Tyrosine: Melanin, Catecholamines, Thyroxine, Norepinephrine, Dopamine.
Don’t Forget to Solve all the previous Year Question asked on Catabolism of carbon skeleton of amino acids

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