Coenzymes: pyridoxal phosphate: 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 · Coenzymes: pyridoxal phosphate

Sample item

A 40-year-old man on isoniazid for tuberculosis develops tingling in his feet. The responsible coenzyme depletion affects which type of reaction?

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

The answer and the reasoning

D. Transamination by aminotransferases

Isoniazid forms a hydrazone with pyridoxal phosphate and increases its urinary loss, producing functional pyridoxine deficiency and peripheral neuropathy, particularly in slow acetylators and malnourished patients. Pyridoxal phosphate is the coenzyme of aminotransferases (ALT, AST), decarboxylases and ALA synthase. Pyridoxine supplements are therefore given with isoniazid.

Option by option

  • A. Oxidative decarboxylation of pyruvate

    Pyruvate dehydrogenase needs thiamine pyrophosphate, lipoate, CoA, FAD and NAD.

  • B. Isomerisation of methylmalonyl-CoA

    Methylmalonyl-CoA mutase needs adenosylcobalamin.

  • C. Carboxylation of pyruvate to oxaloacetate

    Pyruvate carboxylase needs biotin.

  • D. Transamination by aminotransferases (correct)

    Correct. Pyridoxal phosphate is the coenzyme for transamination.

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 D, Transamination by aminotransferases. Isoniazid forms a hydrazone with pyridoxal phosphate and increases its urinary loss, producing functional pyridoxine deficiency and peripheral neuropathy, particularly in slow acetylators and malnourished patients.

Why is "Oxidative decarboxylation of pyruvate" not the answer?

Pyruvate dehydrogenase needs thiamine pyrophosphate, lipoate, CoA, FAD and NAD.

Why is "Isomerisation of methylmalonyl-CoA" not the answer?

Methylmalonyl-CoA mutase needs adenosylcobalamin.

Why is "Carboxylation of pyruvate to oxaloacetate" not the answer?

Pyruvate carboxylase needs biotin.

What concept does this question test?

It tests Coenzymes: pyridoxal phosphate in Biochemistry. Pyridoxal phosphate is the coenzyme of aminotransferases (ALT, AST), decarboxylases and ALA synthase. Pyridoxine supplements are therefore given with isoniazid.

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 Coenzymes: pyridoxal phosphate?

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.