Amino acid biosynthesis/metabolism & Urea Cycle

Amino Acid Carbon Skeletons

transaminase

3-carbon a-keto acid pyruvate is produced from alanine, cysteine, glycine, serine, & threonine. Alanine deamination via Transaminase directly yields pyruvate

The 4-carbon Krebs Cycle intermediate oxaloacetate is produced from aspartate & asparagine. Aspartate deamination via transaminase directly yields oxaloacetate . Aspartate also is converted to fumarate in the Urea Cycle. Fumarate is then converted by Krebs Cycle enzymes in the cytosol (fumerase) to malate, and by Mdh to oxaloacetate

The 4-carbon Krebs Cycle intermediate succinyl-CoA is produced from isoleucine, valine, & methionine

Propionyl-CoA, which is an intermediate on these pathways, is also a product of β-oxidation of fatty acids with an odd number of C atoms fatty acid chains.

Catalytic cycle of Transaminases.

The amino donor is colored blue and the amino acceptor molecule in red.

carbamoyl phosphate synthase I: regulate by N-acetylglutamate

glutaminase - matrix of the mitochondria of the liver

very exothermic - no reverse reaction

ornitine-citruline antiportert

glutamine → liver via other cells

all cells: glutamine synthase (homoduodecamer (8/10/12 subunits int two face to face rings → bifunnel), VERY Allosterically controlled, six way radial symmetry, 3 substrate binding sites: nucleotide, ammonium, amino acid)

ATP binds to the top of the bifunnel that opens to the external surface of GS. Glutamate binds at the bottom of the active site. The middle of the bifunnel contains two sites in which divalent cations bind (Mn+2 or Mg+2). One cation binding site is involved in phosphoryl transfer of ATP to glutamate, while the second stabilizes active GS and helps with the binding of glutamate.