Pyridoxal phosphate is the 5′-phosphate derivative of pyridoxal, a Vitamin B6 form whose ring carries a reactive aldehyde group. It serves as a coenzyme in amino acid chemistry. The phosphate-bearing substituent and the aldehyde have different roles: identifying one does not explain the reactivity of the other.[ref]
Pyridoxal phosphate in ChEBI. CHEBI:18405; definition, structure and classification
An example is 1-aminocyclopropane-1-carboxylate synthase. In a 1990 experiment, chemical reduction with tritium-labelled reagent trapped the coenzyme attached to the enzyme. Subsequent protein digestion and sequencing localized the labelled active-site segment; acid hydrolysis released a modified lysine bearing the pyridoxyl group. This provided chemical evidence for the linkage, beyond observing that adding pyridoxal phosphate improves activity.[ref]
Characterization and sequencing of the active site of 1-aminocyclopropane-1-carboxylate synthase by W. K. Yip and others. PNAS 87, pp. 7930–7934; Abstract, tritiated borohydride labelling and pyridoxyllysine identification
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