Question

The ammonia in urea cycle is produced by

• A. Aspartate
• B. Ornithine
• C. Fumarate
• D. None of the above

Answer 1

The correct option is A Aspartate

An aspartate ammonia-lyase is an enzyme that catalyzes the chemical reaction:

L-aspartate ----->(reversible) fumarate + NH3

This deamination of amino acids results in the production of ammonia (NH3). Ammonia is an extremely toxic base and its accumulation in the body would quickly be fatal. However, the liver contains a system of carrier molecules and enzymes which quickly converts the ammonia (and carbon dioxide) into urea.

So, the correct answer is 'Aspartate'.