Ketogenesis

Step 1

2 acetyl CoA join to become acetoacetyl CoA by using the enzyme acetyl CoA acyl transferase. In this process a CoA is released

Step 2

The acetoacetyl CoA is converted into HMG-CoA by the enzyme HMG-CoA synthase and an insertion of an additional acetyl CoA molecule. A CoA is released as well

This is the rate limiting step

Step 3

HMG-CoA is converted into acetoacetate by the enzyme HMG-CoA lyase, releasing acetyl CoA.

Acetoacetate is a ketone body and it can enter the blood stream

Step 4

Acetoacetate is converted to beta-hydroxybutyrate by the enzyme beta-hydroxybutrate dehydrogenase during which NADH is oxidized to NAD+ because the enzyme is using it as a reducing agent to reduce acetoacetate

beta-hydroxybutrate is a ketone body