Question

2a) Describe (in words) the path that the Amine takes from the degradation of Serine to Carbamoyl phosphate in humans. Use specific biochemical names/terms. (4 points) 2b) There are two carbamoyl phosphate synthetases in humans. The first is used in the Urea cycle. i) Where is the other used? (1 point) ii) Draw the mechanism of the second CPS enzyme below. (Hint, I have about 5 steps in this mechanism. None are complicated, but H2O hydrolysis is needed in the middle.) (6 points) iii) Specifically, where does the Nitrogen end up for the second CPS enzyme? (2 points)

Answer 1

2a) Amino acids undergo degradation in the hepatocytes, where the amino acids are deaminated to give their respective keto acids.Here the amino acid that is deaminated is Serine.  The amine (NH4+) group is released from Serine (its keto acid is pyruvate) after deamination the mitochondrial matrix of the hepatocyte. It then combines with the CO2 released due to the cellular respiration in the mitochondria in the form of bicarbonate (HCO3-) ion to give carbamoyl phosphate in the mitochondrial matrix. The enzyme involved in this reaction is carbamoyl phosphate synthetase

2b) i) Carbamoyl phosphate synthetase II is the enzyme that functions in the cytosol to produce the same product as produced by carbamoyl phosphate synthetase I, that is carbamoyl phosphate, during the de novo synthesis of pyrimidines.

ii) Mechanism of formation of cabamoyl phosphate by carbamoyl sythetase II (CPS II) is as the following:

oro APP I 4o-Crot ADP ut 0 0 UNE O=U-u 12ht lo-co-P-01 4. NTC-07 Cuz си, Bicarbonate си. 0=0-5-F_5_9_o Carboxy ч, Carbamate исти, cro Glutamine АГР Gretamate ADP 0= H₂Nt co-p-o- Reactions catalyzed by Carkamolgt phosphate syntrelase II (CPSI) Overall reaction : 400g + Glutamine + 40 + 2ATP Carbamoye Phosphate Icps II LAPP Carbamoyl Phosphate

iii) The nitrogen is obtained from glutamine amino acid. It is attached to the carbonyl (CO) group of the carbamoyl phosphate.