Metabolic Fates of
Amino Groups
Dietary
Protein Is Enzymatically Degraded to Amino Acids
Pyridoxal
Phosphate Facilitates the Transfer of a-Amino
Groups to Glutamate
BOX 17-1 Assays
for Tissue Damage
Ammonia Is
Formed from Glutamate
Glutamine
Carries Ammonia to the Liver
Alanine
Carries Ammonia from Muscles to the Liver
Ammonia Is
Toxic to Animals
Nitrogen Excretion
and the Urea Cycle
Urea Is
Formed in the Liver
The
Production of Urea from Ammonia Involves Five
Enzymatic Steps
The
Citric Acid and Urea Cycles Are Linked
The
Activity of the Urea Cycle Is Regulated
The Urea
Cycle Is Energetically Expensive
Genetic
Defects in the Urea Cycle Can Be Life-Threatening
Habitat
Determines the Molecular Pathway for Nitrogen
Excretion
Pathways of Amino
Acid Degradation
Several
Enzyme Cofactors Play Important Roles in Amino
Acid Catabolism
Ten Amino
Acids Are Degraded to Acetyl-CoA
Phenylalanine
Catabolism Is Genetically Defective in Some
People
Five
Amino Acids Are Converted into a-Ketoglutarate
Four
Amino Acids Are Converted into Succinyl-CoA
BOX 17-2 Scientific
Sleuths Solve a Murder Mystery
Branched-Chain
Amino Acids Are Not Degraded in the Liver
Asparagine
and Aspartate Are Degraded to Oxaloacetate
Some
Amino Acids Can Be Converted to Glucose, Others
to Ketone Bodies
Summary
Further Reading
Problems
