Ornithine carbamoyltransferase (OTC) catalyzes the reversible transfer of the carbamoyl group from carbamoyl phosphate (CP) to the Nε atom of L-ornithine (ORN) to produce L-citrulline. There are two types of the enzyme – anabolic (aOTC) and catabolic (cOTC). Anabolic OTCs participate in the urea cycle and L-arginine biosynthesis. Catabolic OTCs are part of the catabolic arginine deiminase pathway found in a number of microorganisms. The reported structure is for the anabolic enzyme from pathogen Vibrio vulnificus. The structure has three monomers in the asymmetric unit which form the physiologically active trimer. One of the three enzyme subunits is entrapped in a complex with its first substrate carbamoyl phosphate and its inhibitor arginine. That complex provides additional structural insights into mechanism of inhibition by arginine. It shows that binding of CP together with arginine causes closure of interdomain cleft and brings catalytic loops K*STRTR, B2–H3 and SMG into the catalytic site that adopt conformations same as in the the Michaelis complex. However, binding mode of arginine is substantially different from binding of citrulline, which is the product of the enzymatic reaction.