Apiin is a natural flavonoid, a diglycoside of the flavone apigenin found in the winter-hardy plants parsley and celery, and in banana leaf. The glycoside moiety at carbon-7 of apigenin, O-β-D-apiofuranosyl(→)2-β-D-glucosyl, is carried by several other flavones in parsley plant and seed. The sugar apiose possibly play a role in winter hardiness of celery, duckweed and parsley.
Biosynthesis Apiin is a diglycoside of the flavone, apigenin. Its biosynthesis in plants involves a sequence of enzymes, with chalcone synthase being the one that forms the ring system of the natural product naringenin. Naringenin is then oxidised to apigenin:
Next, the enzyme flavone 7-O-beta-glucosyltransferase transfers a glucose sugar fragment from UDP-glucose, giving apigetrin, with uridine diphosphate (UDP) as byproduct:
Finally, apigetrin is converted to apiin when a second apiose sugar is added by the enzyme flavone apiosyltransferase:
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