Pyridoxal-5-Phosphate

CAS Number	54-47-7 (verified against PubChem CID 1051)
Molecular Formula / MW	C8H10NO6P / 247.14 g/mol
Chemical Class	Phosphorylated pyridine aldehyde — the biologically active coenzyme form of vitamin B6
Relationship to Pyridoxine	Pyridoxine (the common supplement form) is a provitamin; it must be converted to P5P by pyridoxal kinase and PNPO in the liver
Catalytic Role	Forms a Schiff base with amino groups — enabling transamination, decarboxylation, and racemisation
Dependent Pathways	>140 enzymes; synthesis of serotonin, GABA, dopamine, sphingolipids, haem (via ALA synthase), and homocysteine clearance
⚠ Safety	High-dose B6 causes sensory peripheral neuropathy. This is a real, documented, dose-dependent toxicity
Buy from Herbuno	Pyridoxal-5-Phosphate (P5P) Powder →

Name origin: Pyridoxal-5′-phosphate (P5P, or PLP) is the phosphorylated aldehyde form of the pyridine ring that gives the B6 vitamers their family name. The distinction that matters commercially is straightforward: pyridoxine — the form in most supplements and fortified foods — is a provitamin, and must be converted in the liver by pyridoxal kinase and pyridoxine-5′-phosphate oxidase (PNPO) into P5P before it can do anything. P5P is the coenzyme. Traditional use: None applies. Vitamin B6 was identified in the 1930s and P5P characterised as the active coenzyme through mid-century enzymology. Research trajectory: P5P is one of the most catalytically versatile coenzymes in biology, serving more than 140 enzymes. It works by forming a Schiff base — a covalent aldimine — with the amino group of an amino acid substrate, which delocalises electrons into the pyridine ring and enables a remarkable range of transformations: transamination, decarboxylation, racemisation, and β/γ-eliminations. Practically, this places it at the heart of neurotransmitter synthesis (serotonin, GABA, dopamine, via aromatic L-amino acid decarboxylase), haem synthesis (ALA synthase), sphingolipid metabolism, glycogen phosphorylase function, and homocysteine clearance via the transsulfuration pathway. Commercial source: Synthetic. P5P is not a botanical.

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Evidence for Pyridoxal-5-Phosphate Applications

The coenzyme role is established beyond dispute and is worth stating precisely because it grounds every downstream claim. Pyridoxal-5′-phosphate is the biologically active form of vitamin B6 and serves as a coenzyme in enzymatic reactions primarily in amino acid metabolism — transamination, decarboxylation and racemisation — forming a Schiff base with the amino group of amino acids to facilitate these transformations; its involvement in the synthesis of neurotransmitters such as serotonin and GABA, and in glycogen phosphorylase function, extends its reach into neuroscience and glucose metabolism (PubChem CID 1051). Claim strength: High.

The clinical importance of the active form over the provitamin is demonstrated most sharply by the disorders in which the conversion fails. P5P deficiency causes a loss of aromatic L-amino acid decarboxylase in patients and in human neuroblastoma cells, with implications for AADC function and vitamin B6 deficiency states (Allen 2010). This is the mechanistic basis of PNPO deficiency, a rare inborn error causing neonatal seizures that respond to P5P but not to pyridoxine — the clearest possible demonstration that the two forms are not interchangeable in everyone. Claim strength: High.

Whether P5P is superior to pyridoxine for the general population is a genuinely more contested question than the market allows, and honesty requires saying so. The argument for P5P is real: it bypasses hepatic conversion, which requires riboflavin (as FMN) for the PNPO step and is impaired in liver disease, in riboflavin deficiency, in some genetic variants, and by certain drugs. The argument against is that in healthy individuals, conversion is efficient, and that orally administered P5P is in any case dephosphorylated in the intestine to pyridoxal before absorption and re-phosphorylated in tissues — so the ingested phosphate group does not survive to the target. A formulator should understand this rather than repeat the marketing. Claim strength: Emerging (superiority in healthy people).

The safety issue is the most important thing on this page and must not be buried. High-dose vitamin B6 causes sensory peripheral neuropathy — a well-documented, dose-dependent, sometimes irreversible toxicity presenting as numbness, tingling, ataxia and loss of proprioception. This is not a theoretical concern: it is the reason the EU has set a tolerable upper intake level for B6, why several jurisdictions have moved to restrict high-dose B6 supplements, and why B6 is one of the few water-soluble vitamins with a meaningful toxicity ceiling. The paradox is cruel: B6 deficiency causes neuropathy, and so does B6 excess. Claim strength: High.

The homocysteine and neurotransmitter roles are real but should not be over-claimed. P5P is required for cystathionine β-synthase and cystathionine γ-lyase in the transsulfuration pathway, and B6 status is a determinant of homocysteine levels alongside folate and B12 — but the large intervention trials that lowered homocysteine with B-vitamins largely failed to reduce cardiovascular events, and that null should be stated rather than omitted. Similarly, P5P’s role as the AADC cofactor makes it necessary for serotonin and dopamine synthesis, but necessary is not the same as limiting: supplementing a cofactor only helps if the cofactor is what is short. Claim strength: Moderate.

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Dosage & Formulator Specification

Herbuno carries Pyridoxal-5-Phosphate (P5P) Powder. Formulators should note the documented dose-dependent sensory neuropathy risk associated with high-dose vitamin B6 in any form, and should be aware that several jurisdictions restrict high-dose B6 supplements.

Nutritional requirement for vitamin B6 is on the order of 1.3–1.7 mg/day in adults, and typical P5P supplement servings run 10–50 mg. The critical number is the upper one, not the lower: the EU tolerable upper intake level for B6 has been set at 12 mg/day for adults, and doses well below the levels historically associated with severe neuropathy have been implicated in sensory symptoms. A formulator should treat B6 as a nutrient with a real ceiling rather than as an open-ended water-soluble vitamin, should not stack B6 across multiple products in a regimen, and should ensure adequate riboflavin status where the pyridoxine-to-P5P conversion is relevant.

Analytical verification should specify pyridoxal-5′-phosphate by HPLC against a certified reference standard, with related B6 vitamers (pyridoxine, pyridoxal, pyridoxamine and their phosphates) quantified separately, since these are the relevant related substances and the market has seen mislabelling between forms. P5P is light-sensitive and hygroscopic; it degrades on exposure to light and moisture, and photostability data, protective packaging and moisture specification are genuine requirements rather than boilerplate. Because P5P is synthetic, residual solvent testing and route documentation apply.

The dominant safety consideration is sensory peripheral neuropathy from high-dose vitamin B6 — a real, documented, dose-dependent and sometimes irreversible toxicity that presents as numbness, tingling, ataxia and loss of proprioception, and which has driven regulatory restriction of high-dose B6 supplements in several markets. The EU tolerable upper intake level is 12 mg/day for adults. This applies to P5P as much as to pyridoxine, and a supplier who does not state it plainly is failing their customer. Note also that B6 antagonises levodopa when given without a decarboxylase inhibitor, may interact with phenytoin and phenobarbital, and that high-dose B6 has been used to suppress lactation — a relevant consideration in breastfeeding. Anyone experiencing sensory symptoms on B6 should stop and seek medical assessment.

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Frequently Asked Questions — Pyridoxal-5-Phosphate

Is P5P better than pyridoxine?
More contested than the market allows. The argument for is real — it bypasses hepatic conversion, which needs riboflavin and is impaired in liver disease and some genetic variants. The argument against: in healthy people conversion is efficient, and ingested P5P is dephosphorylated in the intestine to pyridoxal before absorption anyway, so the phosphate group does not survive to the target.

Is high-dose vitamin B6 dangerous?
Yes, and this is the most important fact on this page. High-dose B6 causes sensory peripheral neuropathy — numbness, tingling, ataxia, loss of proprioception — which is dose-dependent and sometimes irreversible. The EU tolerable upper intake level is 12 mg/day for adults, and several jurisdictions have restricted high-dose B6 supplements. B6 deficiency causes neuropathy; so does B6 excess.

When does the P5P form genuinely matter?
In PNPO deficiency — a rare inborn error where the enzyme converting pyridoxine to P5P fails. Those neonatal seizures respond to P5P but not to pyridoxine, which is the clearest possible proof the two forms are not interchangeable in everyone. It may also matter in liver disease, riboflavin deficiency, and certain drug interactions.

Does B6 lower cardiovascular risk through homocysteine?
It lowers homocysteine, but that did not translate. P5P is required for the transsulfuration enzymes and B6 status is a determinant of homocysteine alongside folate and B12. However, the large B-vitamin intervention trials that successfully lowered homocysteine largely failed to reduce cardiovascular events. That null should be stated, not omitted.

Related compounds: Benfotiamine, Betaine, Choline, L-Glutathione

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Claim-strength scale – High = multiple human RCTs; Moderate = limited trials or strong preclinical convergence; Emerging = early-stage lab or animal data.

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