Amino acid metabolism Flashcards
What is the concentration of free amino acids in plasma?
Where do free amino acids come from?
Degradation of dietary protein
Synthesis of some proteins
Degradation of endogenous protein
For what are free amino acids used?
For resynthesis of endogenous proteins
Energy production
As precursors for other biological pathways
What happens in essential amino acid deficiency?
Since proteins require pretty much every amino acid, a missing or inadequate intake of a single amino acid can stunt growth in children or lead to protein breakdown in adults
Two primary pathways for protein degradation
ATP-dependent ubiquitin-proteasome system and lysosomal pathway
Relative breakdown time of regulatory proteins
Tend to be degraded and resynthesized faster than other proteins
How much protein is lost every day and must be re-supplied by diet?
55 g
What are examples of body states that would require positive nitrogen balance?
Growth in children, pregnancy, bodybuilding
Major regulated step in the synthesis of urea
Synthesis of carbamoyl phosphate
Where does urea biosynthesis occur?
In the liver
Transamination
Transfer of the amino group to AKG to form glutamate
Cofactor required for transaminases
Pyridoxal phosphate (derivative of B6)
Alanine transaminase blood levels
Shows some sort of inflammation in the liver mostly, as well as some in the pancreas and kidney
Aspartate transaminase blood levels
Shows inflammation/pathology somewhere.
Aspartate transaminase
Glutamate that was just formed donates its nitrogen side chain to oxaloacetate, creating aspartate
Glutamate dehydrogenase
NADP/NAD+ reduces glutamate to alphaketoglutarate and releases the nitrogen group to make ammonium
Major regulated step in the synthesis of urea
Synthesis of carbamoyl phosphate
What is absolutely required in the formation of carbamoyl phosphate?
N-acetylglutamate
Overall reaction of the formation of urea
Aspartate + ammonia + CO2 + 3 ATP + 3 H2O -> urea + fumarate + 2 ADP + AMP + 4 Pi
Where do things take place during urea formation?
Formation of carbamoyl phosphate and citrulline take place in the mitochondria. The others are in the cytosol.
Control of the urea cycle
The amount of glutamate, which is higher postprandially, will lead to higher amounts of N-acetylglutamate and increase the activity of the urea cycle
Main carriers of nitrogen to the liver
Alanine and glutamine
Hyperammonemia
Too high of concentration of ammonia in the blood, which predisposes to coma
Acquired hyperammonemia
Usually due to shunting of blood around the liver due to cirrhosis; ammonia produced from bacteria in the intestines is not converted to urea. Leads to “portal-systemic encephalopathy.”
