U01.01.078 Vitamin B6

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Learning Objectives

  • Identify Pyridoxal Phosphate (PLP) as the active cofactor for transamination and decarboxylation.
  • List the critical neurotransmitters and metabolites synthesized using Vitamin B6.
  • Recognize Sideroblastic Anemia and peripheral neuropathy as key deficiency findings.
  • Understand the pharmacological interaction between Isoniazid and B6 levels.

1. Biochemical Function: The PLP Cofactor

Vitamin B6 (Pyridoxine) is converted into its active form, Pyridoxal Phosphate (PLP). PLP is one of the most versatile cofactors in the human body.

  • Transamination: Essential for the transfer of amino groups (e.g., ALT and AST).
  • Decarboxylation: Used in the synthesis of biogenic amines.
  • Glycogenolysis: A required cofactor for Glycogen Phosphorylase (breaking down glycogen to glucose-1-phosphate).

 

2. Synthesis of Vital Compounds

Vitamin B6 is a “master regulator” of nitrogen metabolism and is required for the synthesis of:

  • Neurotransmitters: Serotonin, Epinephrine, NE, Dopamine, and GABA.
  • Heme: Required for the rate-limiting step of porphyrin synthesis.
  • Niacin (B3): Conversion of Tryptophan to Niacin requires B6.
  • Others: Histamine, Glutathione, and Cystathionine.

3. Deficiency Manifestations

Deficiency is often characterized by neurological and hematological disturbances.

Symptom Pathophysiology/Cause
Sideroblastic Anemia Impaired heme synthesis leads to iron accumulation in mitochondria of RBC precursors (ringed sideroblasts).
Neurological Convulsions, hyperirritability, and peripheral neuropathy (due to decreased GABA and neurotransmitter synthesis).
Inducible Causes Isoniazid (INH) and Oral Contraceptives can precipitate B6 deficiency.

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