Outline

Introduction (Figure 20.1)

Utilization of Inorganic Nitrogen: The Nitrogen Cycle (Figure 20.2)

> Biological Nitrogen Fixation (Diagram, Figure 20.4, Figure 20.5)

> Nitrate Utilization (Figure 20.6, Diagram 1, #2)

Utilization of Ammonia: Biogenesis of Organic Nitrogen (Figure 20.7)

> Glutamate Dehydrogenase: Reductive Amination of -ketoglutarate (Diagram 1, #2)

> Glutamine Synthetase: Generation of Biologically Active Amide Nitrogen (Diagram)

> > Regulation of Glutamine Synthetase (Diagram, Figure 20.9)

> Asparagine Synthetase: A Similar Amidation Reaction (Diagram)

> Carbamoyl Phosphate Synthetase: Generation of an Intermediate for Arginine and Pyrimidine Synthesis (Diagram)

The Nitrogen Economy: Aspects of Amino Acid Synthesis and Degradation

> Metabolic Consequences of the Absence of Nitrogen Storage Compounds

> Biosynthetic Capacities of Organisms (Table 20.1)

> Transamination (Diagram 1, #2, #3)

Protein Turnover

> Quantitative features of Protein Turnover (Table 20.2)

> Biological Importance of Protein Turnover

> Intracellular Proteases and Sites of Turnover (Figure 20.10)

> Chemical Signals for Turnover

> > Ubiquitination (Figure 20.11)

> > Oxidation of Amino Acid Residues

> > PEST Sequences

> > N-Terminal Amino Acid Residue

Amino Acid Degradation and Metabolism of Nitrogenous End Products

> Common features of Amino Acid Degradation Pathways (Diagram, Figure 20.12)

> Detoxification and Excretion of Ammonia

> The Krebs-Henseleit Urea Cycle (Figure 20.13, Figure 21.2, Diagram)

> Transport of Ammonia to the Liver (Figure 20.14, Diagram)

Coenzymes Involved Primarily in Nitrogen Metabolism

> Pyridoxal Phosphate (Figure 20.15, Diagram 1, #2)

> Tetrahydrofolate Coenzymes and One-Carbon Metabolism

> > Discovery and Chemistry of Folic Acid (Diagram)

> > Conversion of Folate to Tetrahydrofolate (Diagram 1, #2, #3)

> > Tetrahydrofolate in the Metabolism of Single-Carbon Units (Figure 20.17, Diagram 1, #2, #3)

> B 12 Coenzymes (Figure 20.18)

> > Coenzyme forms of B 12 (Figure 20.19, Diagram 1, #2)

> > Action of Adenosylcobalamin (Figure 20.20)

> > B 12 Coenzymes and Pernicious Anemia (Figure 20.22)