Metabolism of Acylglycerols and

Sphingolipids

Dr. Abhishek RoyJR II, Dept. of Biochemistry,

Grant Govt. Medical College and Sir JJ Group of Hospitals, Mumbai

Email: mail@abhishek.ro

Lipogenesis: Synthesis of TAG from Glucose

Fate of VLDL Triacylglycerol

A: General structure of GlycerophospholipidB: General Structure of a PlasmalogenC: General structure of SphingolipidsD: General Structure of Glycolipids

Types of glycerolipids and sphingolipids

Overview of Acylglycerol biosynthesis

Biosynthesis of Triacylglycerol and phospholipids

Sites of the hydrolytic activity of phospholipases on a phospholipid substrate.

Role of Phospholipases• Phospholipase A1 removes fatty acyl group from C1• Phospholipase A2- major repair mechanism for membrane lipids

damaged by oxidative free radicals.• Arachidonate is PUFA which can be cleaved to malondialdehyde and

other products in free radical reactions. P-Lipase A2 recognizes the distortion of membrane structure by partially degraded FA and removes it. Acyl transferases then add back a new arachidonate.• Phospholipase C hydrolizes PIP2 to give 2nd messengers DAG and IP3• Phospholipase D cleaves the bond between head group and Phosphate

giving rise to phosphatidate and free alcohol of head group.

Biosynthesis of ether lipids including plasmalogens and PAF

Clinical Importance of Plasmalogen and PAF• Ethanolamine Plasmalogen is found in Myelin• Choline Plasmalogen is found in heart muscle• Plasmalogen synthesis- peroxisomes. Zellweger Syndrome (defect in

peroxisome biogenesis) can lead to even death.• PAF is released from phagocytic blood cells, causes platelet

aggregation, edema and hypotension. It is also involved in allergic response.• PS.- PAF is similar to choline plasmalogen except that the acetyl group

replaces the fatty acyl group at carbon 2 and alkyl group in carbon 1 is saturated.

Synthesis of Phosphatidylcholine/serine/ethanolamine

Metabolism of phosphatidylcholine (Lecithin)

Biosynthesis of ceramide

Synthesis of sphingolipids from ceramide

Biosynthesis of sphingomyelin, galactosylceramide And its sulfo derivative.

Biosynthesis of gangliosides

Clinical Aspects

• Multiple Sulfatase deficiency:• Accumulation of sulfogalactosylceramide, steroid sulfates, and proteoglycans

owing to a combined deficiency of arylsulfatases A, B, and C and steroid sulfatase

• Multiple Sclerosis:• There is loss of both phospholipids (particularly ethanolamine plasmalogen) and

of sphingolipids from white matter• The cerebrospinal fluid shows raised phospholipid levels.

• Infant Respiratory Distress Syndrome• The phospholipid dipalmitoyl-phosphatidylcholine decreases surface tension at

the air–liquid interface.• Deficiency of lung surfactant in the lungs of many preterm newborns gives rise to

infant respiratory distress syndrome (IRDS).

Sphingolipidoses

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