BIOC 302 - Ketone Bodies

what are the ketone bodies

1. acetone

2. acetoacetate

3. D-beta-hydroxybutyrate

which ketone body is exhaled?

acetone

what happens to acetoacetate and D-beta-hydroxybutyrate?

transported to extrahepatic tissues and converted to acetyl-CoA to be oxidized in the TCA cycle

which ketone form is the predominant one in the body?

D-Beta-hydroxybutyrate

ketone synthesis: step 1

thiolase = catalyzes the enzymatic condensation of two acetyl-CoA molecules to form acetoacetyl-CoA

• reversal of the last step of β oxidation

Ketone body synthesis: step 2

HMG-CoA synthase = catalyzes the condensation of acetoacetyl- CoA with acetyl-CoA to form β- hydroxy-β-methylglutaryl-CoA (HMG-CoA)

Ketone body synthesis: step 3

HMG-CoA lyase = catalyzes the cleavage of HMG-CoA to free acetoacetate and acetyl-CoA

Ketone body synthesis: step 4

• acetoacetate decarboxylase = catalyzes the decarboxylation of acetoacetate to acetone OR

• D-β-hydroxybutyrate dehydrogenase = catalyzes the reversible reduction of acetoacetate to D-β-hydroxybutyrate

explain + draw the 3 steps of D-beta-hydroxybutyrate breakdown

1. D-β-hydroxybutyrate dehydrogenase = catalyzes the oxidation of D-β- hydroxybutyrate to acetoacetate in extrahepatic tissue

2. β-ketoacyl-CoA transferase = catalyzes the activation of acetoacetate

3. acetyl-CoA enters the citric acid cycle