urea cycle Flashcards
urea cycle requries two molecules of ATP and is catalyzed by what enzyme
carboamoyl phosphate synthase I (CPS I)
found in high concentrations in the mitochondrial matrix
derived from glutamate via GDH and bicarbonate in liver mitochondria
ornithine transcarbamoylase
condensation of carbamoyl phosphate with amino acid ornithine to form citrulline
argininosuccinate synthetase
citrulline is condensed with aspartate to form argininosuccinate requires both ATP and aspartic acid
- reaction cleaves ATP to adenosine monophosphate and inorganic pyrophosphate
the formation of argininosuccinate incorporates the second nitrogen atom atom destined for urea, what enzme cleaves it?
argininosuccinase cleaves argininosuccinate to arginine and fumarate
arginase
arginine is cleaved by arginase to yield urea and ornithine - completing the cyctle
fumarate and ornithine can reenter cycle, urea enters blood transport to kidney and excreted to urine
regulation of the urea cycle
- N-acetylglutamate = activator of CPS I
- ## arginine = allosteric activator of N-acetylglutamate synthase and ornithine
ornithine transcarbamoylase defect
most common
- x linked inheritance pattern
PKU = phenylketonuria
- deficiency of the enzyme phenylalanine hydrozylase
- hydrozylation of phenylalanine is required step in normal degradation and synthesis of tyrosine in carbon skeleton
- light skin pigmentation
- mental retardation
- unusual gait
- sitting posture
- epilepsy
Alkaptonuria (black urine disease)
- deficiency in enzyme that catalyzes oxidation of homogentistic acid intermidate in tyrosine and phenylalanine
- suffer from deposition of dark pigment in cartilage
- subsequent tissue damage
- severe arthritis
Maple syrup urine disease
- loss of alpha amino group
- loss of decarboxylation step is catalyzed by branched cahin keto acid decarboxylase, a multienzyme complex associated with inner membrane of the mitochondrion
