Enzymes of the Urea Cycle

Enzymes of the Urea Cycle

Introduction:
The urea cycle can be described as a metabolic pathway that uses carbon in CO2 and nitrogen present in glutamate and NH3 to synthesise urea; a mechanism for detoxifying NH3. (Boyer, 2002).
The transformation of NH4+ into urea requires a five-step pathway. This pathway utilises the enzymes Carbamyl Phosphate Synthetase, Ornithine Transcarbamylase, Arginine Synthetase and Arginase in varying amounts to catalyse reactions.

To assay Carbamyl Phosphate Synthetase, citrulline formation from ammonia, bicarbonate and Ornithine is measured, to assay Ornithine Transcarbamylase; citrulline formation from Ornithine and Carbamyl phosphate is measured.
Arginine Synthetase is assayed by measuring urea production from citrulline and Aspartate while Arginase activity can be estimated by measuring urea formation from Arginine. (Mosse, 2003).
Aim:
By assaying Carbamyl Phosphate Synthetase (CPS) and Ornithine Transcarbamylase (OTC), citrulline produc...