Amino Acid Metabolism

Question 1

Amino acids used in protein maintenance come from the ___

Answer 1

Protein/amino acid pool

Question 2

The amino acid pool is supplied by:

Answer 2

Diet (digestion of proteins)

Body’s own degraded tissue

Synthesis of amino acids in the liver

Question 3

The amino acid pool is used to synthesize:

Answer 3

Proteins

Other amino acids

Other nitrogen-containing biomolecules

Question 4

The amino acid pool is used for energy:

Answer 4

When there is excess

When glycogen is consumed (about 12-18 hr after last meal)
- starvation conditions

Question 5

Unlike carbohydrates and fatty acids, amino acids in excess of the body’s immediate needs ____ be stored for later use

Answer 5

Cannot

They are degraded

Question 6

Nitrogen in excess amino acids is converted to:

Answer 6

Ammonium ions
Urea
Uric acid

Excreted

Question 7

Carbon skeletons from excess amino acids are converted to:

Answer 7

Pyruvate
Acetyl CoA
TCA intermediate

Used for:
Energy production
Synthesis of glucose through gluconeogenesis
Converted to triacylglycerols
Converted to ketone bodies

Question 8

Excess from diet or starvation, amino acids used for energy

Answer 8

1. Remove nitrogen by transamination –> oxidative deamination –> NH4+ –> biosynthesis & excess NH4+ converted to urea in liver
2. Carbon skeleton
   —-> pyruvate
   —> gluconeogenesis to make glucose
   —> TCA –> energy

—-> acetyl CoA
—> TCA –> energy
—> triacylglycerol –> energy
—> ketone bodies –> energy

—-> TCA intermediate
—> gluconeogenesis to make glucose
—> other amino acids
—> other molecules (heme groups)

Question 9

Deamination

Answer 9

Removal of alpha-amino group

Two ways:
- transamination
- oxidative deamination

Question 10

Transamination

Answer 10

The first step of most AA

Most common N acceptor is alpha-ketoglutarate

Question 11

Oxidative Deamination

Answer 11

Glutamate is deaminated by glutamate dehydrogenase

Question 12

Transamination General Reaction

Answer 12

Catalyzed by transaminase

AA + a-ketoglutarate
<——–>
a-keto acid + glutamate

Happens in 2 steps:

1. AA + enzyme-PLP —> a-keto acid + enzyme-PLP-NH2
2. enzyme-PLP-NH2 + a-ketoglutarate —> enzyme-PLP + glutamate

Alanine makes pyruvate

Question 13

To carry amino group, aminotransferases need PLP cofactor

Answer 13

PLP is attached covalently to enzyme via Schiff base with a lysine

Question 14

Transamination Steps

Answer 14

1 & 1’: Transamination
- Exchange Schiff base C of PLP to N of amino acid
- Released lysine acts as a general base, removes alpha H

2 & 2’: Tautomerization
- Resonance-stabilized intermediate created by lysine abstraction of H+ followed by protonation at C4 = ketamine

3 & 3’: Hydrolysis
- Ketamine is hydrolyzed to PMP and a-keto acid
- PMP + new acid reverses to produce new amino acid and PLP-enzyme

Question 15

Amino groups of most amino acids are funneled into _____ and _____

Answer 15

Aspartate and glutamate

Question 16

Aminotransferases specific for first amino acid but most use ______ for accepting acid

Answer 16

alpha-ketoglutarate (some oxaloacetate)

Question 17

If oxaloacetate (OAA) is the acceptor, what is the product?

Answer 17

Aspartate

Question 18

Glutamate-aspartate aminotransferase can ____

Answer 18

Interconvert them

Question 19

Muscle aminotransferase use ____ as the acceptor

Answer 19

Pyruvate

Glucose-alanine cycle
Source of glucose

Question 20

Oxidative Deamination General Reaction

Answer 20

Catalyzed by glutamate dehydrogenase

glutamate + H2O + NAD(P)+
<——–>
a-ketoglutarate + NH4+ + NAD(P)H

Question 21

Glutamate Dehydrogenase

Answer 21

Homohexameric

D3 symmetry

Dimer of Trimers