1 Amino Acid Metabolism 1.Proteins are degraded to amino acids 2.Removal of nitrogen is first step in degradation 3.Ammonium is converted into urea 4.C-skeleton enters known pathways 5.Nitrogen fixation -> ammonia production 6.Amino acids are made from intermediates of other pathways 7.Amino acids are precursors

2 Amino Acid Metabolism

3

Protein Turn Over 4 Ubiquitin (8.5 kDa) marks proteins (in eukaryotes) for destruction -> tag Ubiquitin-Activating Enzyme (E1) Ubiquitin-Conjugating Enzyme (E2) Ubiquitin-Protein Ligase (E3)

Protein Turn Over 5 What determines if protein ubiquitinated? -> n-terminal amino acid (N-rule) -> proteins containing PEST sequence Phosphorylation of PEST domains activates ubiquitination Glycosylation of some PEST proteins with N-acetylglucosamine (GlcNAc) has the opposite effect, prolonging the half-life of these proteins. -> Some proteins (e.g., mitotic cyclins involved in regulation of the cell cycle) have a sequence called a destruction box that is recognized by a domain of the corresponding Ubiquitin Ligase. A chain of four or more ubiquitins targets proteins for degradation in proteasomes.

Protein Turn Over 6 Proteasome digests Ub-tagged proteins

7 Amino Acid Metabolism

8 Fate of Nitrogen in Different Organism

9 Amino Acid Degradation 1 st Step -> Removal of Nitrogen

10 Amino Acid Degradation Removal of Nitrogen by aminotransferase Prosthetic group involved in amino transfer

11 Serine and Threonine can be Directly Deaminated Threonine Urea

12 Ammonium Ion is Converted into Urea Urea cycle

13 The Urea Cycle is Linked to the Citric Acid Cycle NH 4 +

14 Fate of the C-Skeleton of Amino Acids

15 Fate of the C-Skeleton of Amino Acids

16 Fate of the C-Skeleton of Amino Acids Aromatic amino acids need oxygenases + O 2

17 Biosynthesis of Amino Acids The nitrogen cycle

18 Biosynthesis of Amino Acids Nitrogen Fixation -> Microorganism

19 Major Ammonium ion carrier Ammonium Ion Is Assimilated into Amino Acids Through Glutamate and Glutamine

20 Biosynthesis of Amino Acids

21 Biosynthesis of Amino Acids in Bacteria and Plants Essential ones are in bold letters

22 Biosynthesis of Amino Acids in Bacteria and Plants

23 In Mammals Plants and bacteria can produce all of them

Feedback inhibition regulates amino acid biosynthesis 24

Amino acids are precursors 25

Amino acids are precursors 26

Amino acids are precursors 27 Heme degradation: -> bilirubin responsible for color of bruises