Vitamins: pyridoxine and isoniazid: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Vitamins: pyridoxine and isoniazid

Sample item

A 45-year-old malnourished man on isoniazid-containing antituberculosis therapy complains of numbness and burning in both feet. Prophylactic pyridoxine would have prevented this. Which type of reaction depends on the coenzyme form of the depleted vitamin?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Transamination of amino acids

Isoniazid forms hydrazones with pyridoxal phosphate and inhibits pyridoxal kinase, depleting the active coenzyme. Pyridoxal phosphate is required for transamination, amino acid decarboxylation, heme synthesis (ALA synthase) and glycogen phosphorylase. Peripheral neuropathy is the main clinical consequence, particularly in malnourished, diabetic or alcoholic patients.

Option by option

  • A. Transamination of amino acids (correct)

    Correct. PLP is the coenzyme of aminotransferases.

  • B. Transfer of one-carbon groups in purine synthesis

    One-carbon transfers in purine synthesis use tetrahydrofolate.

  • C. Oxidative decarboxylation of alpha-keto acids

    Oxidative decarboxylation of alpha-keto acids uses thiamine pyrophosphate, lipoate, CoA, FAD and NAD.

  • D. Carboxylation of pyruvate

    Pyruvate carboxylation uses biotin.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, Transamination of amino acids. Isoniazid forms hydrazones with pyridoxal phosphate and inhibits pyridoxal kinase, depleting the active coenzyme.

Why is "Transfer of one-carbon groups in purine synthesis" not the answer?

One-carbon transfers in purine synthesis use tetrahydrofolate.

Why is "Oxidative decarboxylation of alpha-keto acids" not the answer?

Oxidative decarboxylation of alpha-keto acids uses thiamine pyrophosphate, lipoate, CoA, FAD and NAD.

Why is "Carboxylation of pyruvate" not the answer?

Pyruvate carboxylation uses biotin.

What concept does this question test?

It tests Vitamins: pyridoxine and isoniazid in Biochemistry. Pyridoxal phosphate is required for transamination, amino acid decarboxylation, heme synthesis (ALA synthase) and glycogen phosphorylase. Peripheral neuropathy is the main clinical consequence, particularly in malnourished, diabetic or alcoholic patients.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Vitamins: pyridoxine and isoniazid?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.