Question

Biochemistry

1.

A) Tetrahydrobiopterin serves an essential role in the biosynthesis of one amino acid and several neurotransmitters. What is its function in all those reactions?

B) Pyridoxal P (or pyridoxamine P) is an essential cofactor for what reaction during formation of tryptamine, dopamine and serotonin? What reaction does it facilitate there?

C) Tetrahydrofolate is a vitamin. Why is it required for methionine resynthesis? From what non-protein amino acid is methionine resynthesized?

D) What amino acid provides the C skeleton of cysteine?

E) Describe the overall reaction of serine hydroxymethyl transferase.What form of vitamin B6 (pyridoxine) is needed for this reaction? What form of folic acid is needed?

Answer 1

Ans 1) Tetrahydrobiopterin is one of the essential co-factor for one of three aromatic amino acid hydroxylase enzymes and helps in phenylalanine degradation and production of a number of neurotransmitters like serotonin, melatonin, epinephrine, dopamine etc. The co-factor helps in converting amino acids like phenylalanie, tryptophan etc. to neurotransmitters likes dopamine and serotonin. It helps in conversion of L-tyrosine into L-dopamine, it helps in many neurological functions. It is also one of the key regulators of the nitric oxide synthase in the endothelium and is able to regulate wide range of regulatory functions like monoamine neurotransmitter formation, pain sensitivity etc. It plays a significant role in the cardiovascular diseases as the nitric oxide produced helps in regulation of blood pressure and flow of blood. The availability of the endothelial nitric oxide synthase is dependent on the availability of the tetrahydrobiopterin.

Ans 2) Pyridoxal P is an important co-factor which forms tryptamine, dopamine and serotonin via the transamination of the amino acid. It is basically the active form of Vitamin B6 and helps with the transamination reaction. In this they use the enzyme aminotransferase enzyme where the α-amino group of amino acid substrate tends to displace the ε-amino group of the amino acid and hence produces the product. It helps in converting the levodopa into dopamine by converting the neurotransmitter glutamate to GABA.