the urea cycle

the two nitrogen groups of urea are usually derived from

carbamoyl phosphate and aspartate

why is the urea cycle important?

essential for nitrogen metabolism, helps maintain proper nitrogen balance in the body, and prevents accumulation of toxic ammonia which is a byproduct of metabolism

urea cycle

converts toxic ammonia into a less harmful waste product, urea, which is then excreted in urine

where does the urea cycle take place?

primarily in the liver and involves enzymatic steps in the mitochondria and cytoplasm

carbamoyl phosphate synthetase I

catalyzes the first step where ammonia and bicarbonate convert to carbamoyl phosphate

rate limiting enzyme

ornithine transcarbamoylase

deficiency/missing causes buildup of ammonia in the blood

argininosuccinate synthetase

catalyzes the reaction where AA citrulline and aspartate combine to form argininosuccinate

regulated by levels of citrulline and availability of ATP

argininosuccinate

requires ATP as energy source

argininosuccinate lyase

catalyzes cleavage of argininosuccinate into arginine and fumerate

also involved in citrulline-NO cycle, where arginine is recycled into citrulline and back to arginine

arginase

catalyzes final step of urea cycle, converting arginine into ornithine and urea

arginine can then be further metabolized by arginase