Why are cysteine, glycine and serine not ketogenic amino acids?

[kevv]

Cysteine, glycine and serine could be transaminated to become pyruvate which could then become acety-CoA.
So, as acetyl-CoA could form ketone bodies, why are these amino acids not ketogenic amino acids as well?

---

Members don't see this ad.

 

[JustAPhD]

If I recall*, because the definition of ketogenic states that the AA has to be able to be degraded directly into Acetyl-COA, not modified first. Best of luck on your biochem final/MCAT, don't ask HW questions here.



*It's been awhile since biochem, better double check with someone.

 

[Lawpy]

Cysteine, glycine and serine could be transaminated to become pyruvate which could then become acety-CoA.
So, as acetyl-CoA could form ketone bodies, why are these amino acids not ketogenic amino acids as well?

If I recall*, because the definition of ketogenic states that the AA has to be able to be degraded directly into Acetyl-COA, not modified first. Best of luck on your biochem final/MCAT, don't ask HW questions here.



*It's been awhile since biochem, better double check with someone.

Yep. Take a look at the following diagram

Ketogenic amino acids require direct conversion to acetyl-CoA and/or acetoacetyl-CoA since both can result in immediate production of ketone bodies. This is why there are only 5 amino acids that are both ketogenic and glucogenic (able to produce glucose).