Lipids 7 - Ketone Bodies

Flashcards on Lipids and Ketone Bodies

Ketone Bodies

Acetone, acetoacetate, and b-hydroxybutyrate; synthesized primarily in the liver and are important sources of fuel and energy for many tissues, including brain, heart, and skeletal muscle.

• during periods of starvation ketone bodies may be a major energy source for the brain

Acetoacetate and β-hydroxybutyrate

Normal substrates for kidney cortex and for heart muscle.

Thiolase

Catalyzes the condensation of two molecules of acetyl-CoA to form acetoacetyl-CoA in ketone body synthesis; the same enzyme that carries out the thiolase reaction in β-oxidation, but here it runs in reverse.

HMG-CoA lyase

Converts HMG-CoA (from second reaction) to acetoacetate and acetyl-CoA in a mixed aldol-Claisen ester cleavage reaction during ketone body synthesis.

β-hydroxybutyrate dehydrogenase

A membrane-bound enzyme that can reduce acetoacetate to β-hydroxybutyrate.

Acetoacetate

The first ketone produced that can be used directly or converted to one of the other ketones; a true ketone.

β-Hydroxybutyrate

The most prevalent ketone which is formed from acetoacetate; not a true ketone but considered a ketone body.

Acetone

Formed as a side product of acetoacetate which undergoes rapid breakdown and exits the body in breath and urine.

Keto esters

Taken as performance enhancers for athletes and for those on ketogenic diets, under ongoing research focus, and even fueling the brain in Alzheimer’s disease.

Type 1 Diabetes (10% of all cases)

Elevated blood glucose results from inadequate secretion of insulin by the islets of Langerhans in the pancreas, leading to increased gluconeogenesis and ketone body production.

consumes most of the avaliable oxaloacetate but breakdown of fat produces large amounts of acetyl CoA which cannot enter the citric acid cycle, resulting in large amounts of ketone bodies.

Type 2 Diabetes (90% of all cases)

Normal or even elevated levels of insulin, but their cells are not responsive to insulin, often due to a shortage of insulin receptors leading to increased gluconeogenesis and ketone body production.