Flashcards in Protein Biochemistry 2 Deck (19):
The relative directionality of the reactions catalyzed by AST and ALT is determined by ____________.
the concentrations of the reactants
Because ___________ is toxic, glutamine is used to transport it from the tissues to the liver.
The enzyme _____________ is located in peripheral tissues.
After glutamine gets to the liver, what happens?
Glutaminase breaks off one NH3 which goes into the production of urea.
Two things happen in the kidneys regarding urea: _____________.
ammonia is removed from glutamine and urea is disposed
What enzyme in the urea cycle is an anti-cancer drug?
Asparaginase (which deprives cells of asparagine)
What enzyme is defective in someone with maple-syrup urine disease?
Branched-chain alpha-keto-acid dehydrogenase
Thyroxin is made from ______________.
The active form of thyroxin is cleaved be which enzyme?
Deiodinase (which activates T3 from T4)
Trace the urea cycle.
NH4 + HCO3
(Mitochondrial carbamoyl phosphate synthetase) ***Rate-limiting; uses ATP***
(Mitochondrial ornithine transcarbamoylase) **Ornithine enters***
(Cytosolic arginosuccinate synthetase) ***Aspartate enters; requires ATP***
(Cytosolic arginosuccinate lyase)
Arginine and fumarate
Urea and Ornithine
_____________ is an allosteric activator of carbamoyl phosphate synthetase.
Why do muscles use ALT instead of AST?
Because muscle accumulates pyruvate, which can be shuttled into alanine
Describe how ALT and AST "feed" the urea cycle.
ALT produces glutamate, which can release an NH4+ molecule (that enters the urea cycle) by glutamate dehydrogenase. AST can produce aspartate (when the concentration is low) which enters the urea cycle.
What protein helps transport urea-cycle reactants to their necessary locations?
ORNT1, which moves citrulline out of the mitochondria and ornithine in.
Glutamine transport in the brain is necessary because _______________.
glutamate cannot cross the BBB
Glutamate dehydrogenase goes both ways and thus serves as a control point for protein catabolism. What things allosterically stimulate the breakdown of glutamate?
All things that signal low-energy states: ADP, GDP
__________ degrades arginine to citrulline and a neurotransmitter.
Ornithine and creatine phosphate (a source of energy for muscle) are synthesized from what two reactants?
Arginine and glycine