catecholamine synthesis

Question 1

What is the rate-limiting enzyme in catecholamine synthesis?

Answer 1

Tyrosine Hydroxylase

Question 2

Which amino acid is the immediate precursor to catecholamine synthesis?

Answer 2

L-Tyrosine

Question 3

Which cofactor is required by both Phenylalanine Hydroxylase and Tyrosine Hydroxylase?

Answer 3

Tetrahydrobiopterin (BH4)

Question 4

Which vitamin is a mandatory cofactor for DOPA Decarboxylase?

Answer 4

Vitamin B6 (Pyridoxal Phosphate/PLP)

Question 5

Why is Vitamin B6 restricted in Parkinson’s patients taking Levodopa?

Answer 5

It increases peripheral conversion of Levodopa to Dopamine (decreasing CNS availability).

Question 6

Which catecholamine synthesis enzyme is located inside synaptic vesicles rather than the cytoplasm?

Answer 6

Dopamine β-hydroxylase

Question 7

What are the two essential cofactors for Dopamine β-hydroxylase?

Answer 7

Vitamin C (Ascorbic acid) and Copper (Cu2+)

Question 8

Which enzyme converts Norepinephrine to Epinephrine?

Answer 8

PNMT (Phenylethanolamine N-methyltransferase)

Question 9

Which hormone induces the synthesis of PNMT in the adrenal medulla?

Answer 9

Cortisol

Question 10

What is the universal methyl donor required by PNMT for Epinephrine synthesis?

Answer 10

SAM (S-adenosylmethionine)

Question 11

What is the major urinary metabolite of Epinephrine and Norepinephrine?

Answer 11

Vanillylmandellic Acid (VMA)

Question 12

What is the major urinary metabolite of Dopamine?

Answer 12

Homovanillic Acid (HVA)

Question 13

A deficiency in BH4 leads to which ‘malignant’ condition?

Answer 13

Malignant Phenylketonuria (PKU)

Question 14

High levels of urinary VMA are a diagnostic marker for which tumor?

Answer 14

Pheochromocytoma

Question 15

Which drug acts as a competitive inhibitor of Tyrosine Hydroxylase?

Answer 15

Metyrosine

Question 16

Where in the cell does the conversion of Norepinephrine to Epinephrine occur?

Answer 16

Cytoplasm (after NE leaks out of the vesicle)