Amino Acid Flow In/Out of TCA Cycle
- Pyruvate
- Alanine (3C) produces pyruvate via transamination (in which Alpha-Ketoglutarate is the alpha– ketoacid)
- Serine (3C) converts via non–oxidative deamination, which directly releases serine’s alpha amino group via serine dehydratase
- Cysteine (3C) can convert to pyruvate through numerous different means.
- Threonine (4C) converts to pyruvate through an intermediary.
- Glycine (2C) and serine can reversibly interconvert.
- Oxaloacetate
- Aspartate transaminates into oxaloacetate via the AST (in which alpha ketoglutarate is the acceptor).
- Asparginase hydrolyzes asparagine to ammonium (ie, it removes the nitrogen from the R group) and aspartate, which is then transaminated to oxaloacetate
- Fumarate
- Phenylalanine degrades to tyrosine via the oxygenase: phenylalanine hydroxylase
- Tyrosine can interconvert with phenylalanine
- Aspartate (4C) can convert to fumarate via the urea cycle
Carbon Skeleton of Amino Acids
Carbon Skeletons of Amino Acids
- Amino acid carbon skeletons are transformed into major metabolic intermediates that can be:
- Oxidized via the TCA Cycle
- Converted to Glucose
- Seven key intermediates, so we can start to commit them to memory:
- Pyruvate
- Acetyl CoA
- Acetoacetyl CoA
- Alpha-Ketoglutarate
- Succinyl CoA
- Fumarate
The flow of amino acids into/out of the TCA cycle via their keto acid counterparts.
- We assign these intermediates as being either:
- Glucogenic, which means that the intermediates degrade into glucose occurs via phosphoenolpyruvate.
- Ketogenic, which means that the intermediates degrade to ketone bodies or fatty acids.
- We'll see that certain amino acids end up on both camps: glucogenic and ketogenic.