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What is the key reaction in the degradation of many amino acids?
transamination
What are the two steps of transamination?
transaminase produces an alpha-keto acids
glutamate dehydrogenase regenerates alpha-ketoglutarate and produces ammonia
What happens in aminotransferase?
the NH3+ and double bonded O "switch" places
Glutamate dehydrogenase reaction
Major route for oxidative deamination
Regenerates the amino acceptor (α-ketoglutarate) and provides ammonia, either for re-utilization or disposal as urea
glutamate + NAD+ + H2O > α-ketoglutarate + NADH + NH3
pyridoxal phosphate (PLP)
The active coenzyme form of vitamin B6 (6 forms)
How is the pyridoxine cofactor bound to the enzyme? How is the binding spot displaced?
bound via lysine to the active site and is displaced by substrate binding
What is the committed step of the urea cycle?
the formation of the carbamoyl phosphate
What is the first step of the urea cycle?
coupling of ammonia with bicarbonate
What is the second step of the urea cycle?
formation of citrulline
What is the third step of the urea cycle?
process: formation of arginosuccinate (from citrulline + aspartate)
enzyme: arginosuccinate synthase
What is the fourth step of the urea cycle?
arginosuccinate is cleaved into arginine and fumarate
What is the fifth step in the urea cycle?
process: formation of ornithine + urea (from arginine)
enzyme: arginase
Where does the urea cycle take place?
cytosol and mitochondrial matrix
what is the key intermediate that links the urea cycle to the citric acid cycle?
arginosuccinate
converted to arg which is used in the urea cycle and fumarate which is converted to oxaloacetate in the citric acid cycle
What is the "fate" of oxaloacetate?
transamination forms aspartate which is used in the urea cycle and biosynthesis
gluconeogenesis to form glucose
citric acid cycle to form ATP
What are the glucogenic amino acids?
alanine, cysteine, glycine, serine, threonine, asparagine, aspartate, methionine, valine, arginine, glutamate, glutamine, histidine, proline
What are the ketogenic amino acids?
leucine, lysine
Which are both?
phenylalanine, isoleucine, tryptophan, tyrosine
transamination of alanine and alpha-ketoglutarate produces what?
pyruvate and glutamate
What are the two pathways of aspartate?
oxaloacetate via transamination or fumarate via the urea cycle
What does glutaminase do?
converts glutamine to glutamate and NH4+ and then to alpha-ketoglutarate
What are the metabolic intermediates if the ketogenic amino acids?
acetyl CoA and Acetoacetyl CoA
What is an acceptor group for amino acids during catabolism?
alpha-ketoglutarate
How is the urea cycle connected to gluconeogenesis?
fumarate and oxaloacetate