answer was acetyl CoA. I referred NCERT. There is one flow diagram where entry of various substrates is shows and according to that proteins are broken down to AAs and then enter at the level of pyruvic acid. Text mentions they can enter at acetyl CoA or pyruvic acid level. please clarify.
Pyruvic acid and acetyl CoA are intermediate compounds produced during oxidation of all types of respiratory substrates carbohydrates, fats, proteins.