= Pyridoxal
<Pyridoxal> is an aldehyde-containing member of the <Vitamin B6> family, with formula $\mathrm{C_8H_9NO_3}$. Its substituted pyridine ring carries methyl, hydroxy and hydroxymethyl groups as well as the <aldehyde> group. It differs chemically from the phosphorylated <coenzyme> <pyridoxal phosphate>.<Pyridoxal in ChEBI>[CHEBI:17310, Definition and Formula]{ref}
The distinction can be located in the structure. Formation of <pyridoxal phosphate> modifies the primary alcohol group through a phosphate ester; it does not mean that the two names are interchangeable descriptions of one unchanged compound.<Pyridoxal phosphate in ChEBI>[CHEBI:18405, monophosphate ester at the primary hydroxy group]{ref} The broader <Vitamin B6> family also includes other chemical forms.<Vitamin B6 Fact Sheet for Health Professionals by the Office of Dietary Supplements>[Introduction, vitamers]{ref}
A simple assay example illustrates the implication. Suppose one sample contains a measured amount of free <pyridoxal> and another the same molar amount of <pyridoxal phosphate>. The molecular counts can match while charge, binding and catalytic availability differ. Interpreting a <coenzyme>-dependent reaction requires identifying the actual form supplied and any conversion steps, rather than inferring functional equivalence from the shared vitamin-family name.
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