Answer- Case study- Oral contraceptives induced vitamin deficiencies

Case Details

Oral contraceptives are known to lower blood levels of folate and vitamin B6. Which of the following conversion processes might be directly affected?

A. Ornithine to Citrulline

B. Histidine to histamine

C. Glutamate to Glutamine

D. Propionyl co A to Methyl malonyl co A

E. Phenyl alanine to Tyrosine

Answer- B- The correct answer is conversion of Histidine to histamine. The reaction is catalyzed by decarboxylase that requires B6-P as a cofactor (Figure-1) that gets deficient in women upon long-term oral contraceptive usage. Folic acid is not required in this reaction.

Histidine to histamine

Figure-1- Decarboxylation of Histidine is carried out by histidine decarboxylase. Histamine is an important chemical for allergies and anaphylaxis.PLP is pyridoxal phosphate(B6-P)

The conversion of Ornithine to citrulline (Figure-2) takes place in urea formation. None of these vitamin B6 or folic acid is required in this conversion process.

ornithine to citrulline conversion

Figure-2- Ornithine to citrulline conversion is carried out by ornithine transcarbamoylase, which is an important mitochondrial enzyme required for urea synthesis.

Glutamate to glutamine conversion is catalyzed by glutamine synthetase (figure-3). It is a reaction to detoxify ammonia, the first line of defense in brain. These vitamins are not required in this reaction process.

Glutamate to glutamine conversion

Figure-3- Gamma glutamyl phosphate is an intermediate in the conversion of Glutamate to glutamine,

Propionyl co A to Methyl malonyl co A conversion requires biotin as a coenzyme (figure-4). It is a carboxylation reaction; ATP is also required for this process.


Figure-4- Propionyl co A to methyl malonyl co A conversion is an intermediate step in the actual conversion of propionyl co A to Succinyl co A, which is an intermediate of TCA cycle.

Phenyl alanine to Tyrosine conversion requires Tetrahydrobiopterin (BH4) as a coenzyme. The reaction is catalyzed by Phenyl alanine hydroxylase and it is the first step of metabolism of phenyl alanine (figure-5)

Phenyl alanine to tyrosine

Figure-5- Phenyl alanine hydroxylase catalyzing the conversion of phenyl alanine to tyrosine is a mono oxygenase, deficiency of which causes Phenylketonuria.

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