28 - Biologically Active Amines

Question 1

What is thyroxine?

Answer 1

A hormone containing iodine modified turosine

Melanine derived from tyrosine as well

Catecholamines are tyrosine metabolites that act as both neurotransmitters and as hormones

Question 2

What is the precursor to serotonin?

Answer 2

Tryptophan

Question 3

How do most amino acids acquire hormonal or neurotransmitter activity?

Answer 3

Decarboxylation

Decarboxylases are found in neurons, adrenal cells and the intestines
- Requires pyridoxal phosphate as a cofactor and a Schiff base intermediate

Question 4

Give three PLP dependent reactions

Answer 4

• Transamination
• Serine dehydratase
• Amino acid decarboxylase

Question 5

How is GABA inactivated?

Answer 5

Transamination with aKG (rather than be MAO)

Question 6

What are the two steps of serotonin synthesis from tryptophan?

Answer 6

1. Ring hydroxylation

2. Side chain decarboxylation

Question 7

What can iodine deficiency cause?

Answer 7

Goiter (thyroid enlargement) as the organ expands to acquire all available iodine

Question 8

What are the catecholamines?

Answer 8

• Dopamine
• Norepinephrine
• Epinephrine

Produced by adrenal gland & neurons

Question 9

Give the four steps for synthesizing catecholamines

Answer 9

1. Tyrosine hydroxylated to DOPA via tyrosine hydroxylase (KO lethal, rescue with DOPA)
2. DOPA decarboxylated to dopamine
3. Side chain hydroxylation to norepinephrine
4. Methylation of amino group for epinephrine (uses SAM)

Question 10

What is the most common type of neurotransmitter inactivation?

What are some other ways?

Answer 10

Removal of the amine function by oxidation on the outer membrane of the mitochondria
- Inactivated by MAO, converting amine function to an inactive aldehyde

Other:
- O-methylation of catechol ring by COMT (converts to metanephrines)

Question 11

Give two disorders of catecholamine metabolism

Answer 11

Parkinson’s disease
- Low dopamine

Pheochromocytoma

• Tumors of adrenal medulla
• Extra epinephrine and norepinephrine causes hypertension because of vasoconstrictor properties

Question 12

Give two disorders of catecholamine metabolism

Answer 12

Parkinson’s disease
- Low dopamine

Pheochromocytoma

• Tumors of adrenal medulla
• Extra epinephrine and norepinephrine causes hypertension because of vasoconstrictor properties
• Can detect by looking for metanephrines and plasma catecholamine levels