Citrulline is formed from ornithine and carbomoyl phosphate. The carbomoyl phosphate donates its carbomoyl group to orinithine. Ornithine has a similar rle to that of oxaloacetate in the citric acid cycle.
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Where does this happen?
It starts in the mitochondrion, then the newly form ed citrulline passes into the cytosol
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What is the second stage?
Formation of argininosuccinate
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Which enzyme?
Argininosuccinate synthetase
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How?
Requires ATP and proceeds trhough a citrullyl-AMP intermediate
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What is the third stage?
Formation of arginine
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Which enzyme?
Argininosuccinase
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How?
Cleavage of argininosuccinate to form arginine and fumarate (which enters the mitochondria to become part of the citric acid cycle)
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What is the fourth stage?
Formation of urea
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Which enzyme?
Argininase
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How?
Cleavage of arginine, to form urea and ornithine (which is transported to the mitochondrion to initiate another urea cycle)
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How many ATP are used?
1, in the formation of Argininosuccinate from citrulline
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