Introduction

Ornithine transcarbamoylase (OTC), also called ornithine carbamoyltransferase, is an enzyme that catalyzes the reaction between carbamoyl phosphate (CP) and ornithine (Orn) to form citrulline (Cit) and phosphate (P).  In plants and microbes OTC is involved in arginine biosynthesis.  In mammals it is located in the mitochondria and is part of the urea acid cycle. (1)  OTC has three identical subunits that undergo very little cooperativity or inhibition. There exist over 100 human mutations in OTC that cause hyperammonemia, a toxic level of ammonia in the blood, and subsquent neurological damage or even death that have been identified. (2)  Better understanding of how this enzyme works could lead to better treatment of hyperammonemia.