2. Digestion sf lipids by pancreatic enzymes
The pancreatic enzymes are primarily responsible
for the degradation of dietary triacylglycerols,
cholesteryl esters and phospholipids.
Degradation of triacylglycerols
Pancreatic lipase is the major enzyme that digests
dietary fats. This enzyme preferentially cleaves
fatty acids (particularly long chain, above 10
carbons) at position 1 and 3 of triacylglycerols.
The products are monoacylglycerol and free fatty
acids
3. A specific enzyme namely pancreatic cholesterol
esterase (cholesteryl ester hydrolase) cleaves cholesteryl
esters to produce cholesterol and free fatty acids.
Phospholipases are enzymes responsible for the
hydrolysis of phospholipids.
These fatty acids are absorbed with the help of bile salts.
Oxidation of Fatty acids
The fatty acids in the body are mostly
oxidized by B-oxidation. p-Oxidation may
be defined as the oxidation of fatty acids
on the p-carbon atom. fhis results in the
sequential removal of a two carbon
fragment, acetyl CoA.
4. The β-oxidation of fatty acids involves three
stages
l. Activation of fatty acids occurring in the
cytosol;
ll. Transport of fatty acids into mitochondria;
lll. β Oxidation proper in the mitochondrial
matrix.
1. Fatty acids are activated to acyl CoA by
thiokinases or acyl CoA synthetases. The
reaction occurs in two steps and requires ATP,
coenzyme A and Mg2+
The inner mitochondrial membrane is
impermeable to fatty acids. A specialized
5. SATURATED FATTY ACIDS
1.Acyl group of acyl CoA is transferred to
carnitine (B-hydroxy T-trimethyl
aminobutyrate), catalysed by carnitine
acyltransferase I (present on the outer
surface of inner mitochondrial membrane).
2. The acyl-carnitine is transported across
the membrane to mitochondrial matrix by a
specific carrier protein.
3. Carnitine acyl transferase ll (found on the
inner surface of inner mitochondrial
membrane) converts acyl-carnitine to acyl
6. Each cycle of p-oxidation, liberating a two carbon unit-acetyl
CoA, occurs in a sequence of four reactions
1. Oxidation : Acyl CoA undergoes dehydrogenation by an
FAD-dependent flavoenzyme, acyl CoA dehydrogenase. A
double bond is formed between o and p carbons (i.e.,2 and 3
carbons).
2. Hydration : Enoyl CoA hydratase brings about the
hydration of the double bond to form p-hydroxyacyl CoA.
3. Oxidation : p-Hydroxyacyl CoA dehydrogenase catalyses
the second oxidation and generates NADH. The product
formed is p-ketoacyl CoA.
4. Cleavage : The final reaction in p-oxidation is the
liberation of a 2 carbon fragment, acetyl CoA from acyl CoA.
This occurs by a thiolytic cleavage catalysed by p-ketoacyl
CoA thiolase (or simply thiolase).
The new acyl CoA, containing two carbons less than the
original, reenters the p-oxidation cycle. The process
