Fatty Acid Oxidation Vocabulary

A set of vocabulary flashcards covering the enzymes, intermediates, pathways, and cofactors involved in mitochondrial β-oxidation of saturated, unsaturated, and odd-chain fatty acids.

Fatty acid oxidation

Mitochondrial pathway that breaks down fatty acids into acetyl-CoA, FADH2, and NADH via repeated β-oxidation cycles.

Palmitic acid (16:0)

16-carbon saturated fatty acid

ATP yield from palmitate

8 Acetyl CoA → 8 CAC = 3 NADH, 1 FADH2, 1 GTP → 24 ATP + 8 ATP + 8 ATP
7 rounds of beta-oxidation = 7 FADH2, 7 NADH

total: 31 NADH → 77.5 ATP; 15 FADH2 → 22.5 ATP; 8 GTP → 8 ATP

Unsaturated fatty acid oxidation

Requires two addition enzymes: an isomerase and reductase

unsaturated fatty acid examples

Oleic acid (9-cis-octadecenoic acid), Linoleic acid (9,12-cis-octadecadienoic acid)

oxidation of fatty acyl-CoA step 1: oxidation

Fatty acyl-CoA + FAD → (via acyl-CoA DH) trans-delta 2-Enoyl-CoA + FADH2

e- Transfer Flavoprotein

FADH2 → FAD + ETFox → ETFred + ETF:ubiquisone oxidoreductase(ox) → ETF:ubiquinone oxioreductase(red) + Q → QH2 → mitochondrial ETC → ATP + H2O

beta oxidation step 2: hydration

trans-delta 2-enoyl-CoA + H2O → (via enoyl-CoA hydratase) 3-L-Hydroxyacyl-CoA

beta oxidation step 3: oxidation

3-L-Hydroxyacyl-CoA + NAD+ → (via 3-L-hydroxyacyl-CoA DH) B-Ketoacyl-CoA + NADH + H+

beta oxidation step 4: thiolytic reaction

B-Ketoacyl-CoA + CoA-SH → (via B-ketoacy-CoA thiolase) Fatty acyl-CoA (2 C shorter) + Acetyl-CoA

beta-oxidation of monounsaturated fatty acid step 1

Oleoyl-CoA → (B oxidation until cis-delta 3-enoyl-CoA) + 3 Acetyl-CoA. This product cannot serve as a substrate for enoyl-CoA hydratase, which only acts on trans double bonds

beta-oxdation of monounsaturated step 2:

cis-delta 3-Dodecanoyl-CoA → (via delta 3-delta 2-enoyl-CoA isomerase) trans-delta 2-dodecenoyl-CoA → (beta-oxidation, 5 cycles) 6 Acetyl-CoA

beta-oxidation of 18:2 polyunsaturated fatty acid step 1:

linoleoyl-CoA cis-delta 9, cis-delta 12 → (beta-oxidation x3 cycles) Acetyl-CoA + cis-delta 3, cis-delta 6 US fatty acid. This intermediate cannot be used because it’s double bonds are cis, not trans

beta oxidation of polyunsaturated fatty acid step 2

cis-delta 3, cis-delta 6 → (via delta 3, delta 2-enoyl-CoA isomerase) trans-delta 2, cis-delta 6 → (beta-oxidation: 1 cycle + 1st oxidation of 2nd cycle) trans-delta 2, cis-delta 4

beta-oxidation of polyunsaturated fatty acid step 3

trans-delta 2, cis-delta 4 → (via 2,4-dienoyl-CoA reductase) trans-delta 3 → (via enoyl-CoA isomerase) trans-delta 2 → (beta oxidation - 4 cycles) 5 Acetyl-CoA

beta-oxidation of fatty acids with odd number of carbons

The substrate for the last cycle through the beta-oxidation sequence is a fatty acyl CoA with a 5-carbon fatty acid. Oxidation and cleavage generates acetyl-CoA and propionyl CoA

beta-oxidation w/ odd carbons step 1

Propionyl-CoA + HCO3- + ATP + biotin cofactor → (via propionyl-CoA carboxylase) D-methylmalonyl-CoA + ADP + Pi

beta-oxidation w/ odd carbons step 2

D-methylmalonyl-CoA → (via methylmalonyl-CoA epimerase) L-methylmalonyl-CoA

beta-oxidation w/ odd carbons step 3

L-methylmalonyl-CoA → (via methylmalonyl-CoA mutase + coenzyme B12) Succinyl-CoA → CAC