Presentation on theme: "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."— Presentation transcript:
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
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