Oxidation stages of fatty acids

What are the main stages of this process?

Coconut oil contains fatty acids [Wikimedia]

The ox­i­da­tion of fat­ty acids is not so much a chem­i­cal as a bio­chem­i­cal process, as this cy­cle of re­ac­tions takes place in the or­gans of liv­ing or­gan­isms. The process is quite com­plex, as it in­cludes many stages. Ox­i­da­tion of fat­ty acids in bio­chem­istry is called beta-ox­i­da­tion. This is no ac­ci­dent – the process re­ceived this name as in the car­boxyl group (-COOH) dur­ing re­ac­tion, the third atom of car­bon ox­i­dizes, which cor­re­sponds to the beta po­si­tion. The acetyl group (CH₃-CO-) also sep­a­rates, which con­tains the first two car­bon atoms.

Why ox­i­da­tion takes place

Adenosine triphosphate (ATP) 3D structure [Wikimedia]

Fat­ty acids con­tain en­er­gy which must be re­leased for the cor­rect me­tab­o­lism in the or­gan­ism and syn­the­sis of ATP (adeno­sine triphos­phate), with­out which me­tab­o­lism is im­pos­si­ble. So there is a meta­bol­ic route by which fat­ty acids are trans­formed into car­bon diox­ide and wa­ter, with the re­lease of en­er­gy sup­ply. The process takes place in mi­to­chon­dria. Thus all cells apart from nerve cells are ca­pa­ble to a greater or less­er de­gree of ox­i­diz­ing fat­ty acids.

Ox­i­da­tion stages

4 main stages of ox­i­da­tion of fat­ty acids in the body may be sin­gled out:

  1. Ac­ti­va­tion of mol­e­cule of fat­ty acids in the cy­tosol (the coen­zyme A at­tach­es to it with the for­ma­tion of acyl-S-CoA);
Carnitine [Wikimedia]
  1. Bond­ing of the ob­tained sub­stance with the vi­ta­min-like sub­stance car­ni­tine for the move through the mem­brane of mi­to­chon­dria, on the mem­brane is the re­spec­tive en­zyme con­tain­ing car­ni­tine – car­ni­tine-actyl­trans­ferase-1;

  2. The move of fat­ty acid through the mem­brane with the en­zyme of tran­sclo­case: en­zyme of car­ni­tine-acyl­trans­ferase-2 once more forms acyl-S-CoA, which is sub­se­quent­ly ox­i­dized.

Di­rect ox­i­da­tion of fat­ty acids is a process that in­cludes the cycli­cal rep­e­ti­tion of 4 re­ac­tions:

  1. Ox­i­da­tion (acyl-S-CoA-de­hy­dro­ge­nase forms);

  2. Hy­dra­tion (enoil-S-CoA-hy­dratase is ob­tained);

  3. Ox­i­da­tion of the 3ʳᵈ car­bon atom (hy­drox­y­a­cyl-S-CoA-de­hy­dro­ge­nase is formed);

  4. Sep­a­ra­tion of acetyl-S-CoA and at­tach­ment of HS-CoA.

Af­ter pass­ing through all the stages, the mol­e­cule re­turns to the first ox­i­da­tion re­ac­tion. The process con­tin­ues as long as the break of the di­car­bon links of the fat­ty acid can take place. When 2 mol­e­cules of acetyl-S-CoA form, the ox­i­da­tion ends. The mol­e­cules formed are ox­i­dized in the Krebs cy­cle.

Capric acid 3D structure (it is a fatty acid) [Wikimedia]

Here there are lots of ex­per­i­ments where ox­i­da­tion of dif­fer­ent sub­stances is used too.

How ob­tained en­er­gy is cal­cu­lat­ed

The en­er­gy ben­e­fit of the ox­i­da­tion re­ac­tion of these acids can be cal­cu­lat­ed. The fol­low­ing fac­tors in­flu­ence it:

  1. The amount of ATP ex­pend­ed on ac­ti­va­tion of the fat­ty acid mol­e­cule (cor­re­sponds to two macroer­gic bonds – 2 ATP mol­e­cules are spent, which are sub­se­quent­ly sub­tract­ed from the to­tal num­ber of ATP mol­e­cules syn­the­sized in the re­ac­tion);

  2. The num­ber of dou­ble bonds in the fat­ty acid (if they are present in the ini­tial mol­e­cule, the stage of for­ma­tion of the dou­ble bond in the fat­ty acid mol­e­cule in its ox­i­da­tion can be skipped);

  3. The num­ber of acetyl-S-CoA coen­zymes formed for the re­ac­tion (to de­ter­mine this, the num­ber of car­bon atoms in the car­bon chain of the acid should be di­vid­ed by 2);

  4. The num­ber of ox­i­da­tion cy­cles that take place com­plete­ly (the num­ber of pos­si­ble breaks be­tween di­car­bon chains of acid cor­re­sponds to the num­ber of pos­si­ble acts of beta-ox­i­da­tion).

De­pend­ing on this, the fi­nal amount of syn­the­sized ATP mol­e­cules is de­ter­mined.

Ox­i­da­tion of fat­ty acids is an im­por­tant bio­chem­i­cal re­ac­tion which takes place in the or­gan­isms of liv­ing crea­tures. It has a sig­nif­i­cant in­flu­ence on the syn­the­sis of ATP mol­e­cules, and so it nec­es­sary for cor­rect me­tab­o­lism in the or­gan­ism.