Abstract
LC-Orbitrap-MS provides accurate monoisotopic masses which enable the prediction of molecular formulas of individual compounds. It is well-known that some of the oxygen atoms found in natural products are incorporated from molecular oxygen by the action of monooxygenases such as cytochrome P450s. Incorporation of the oxygen atoms into metabolites is one of the driving forces leading to the diversification of natural products. To clarify the origin of the oxygen atoms in metabolites, we conducted an incorporation experiment with molecular 18O2 using two phototrophs (Lotus japonicus and Physcomitrella patens).
L. japonicus was grown with molecular 18O2 for a short term (one week) or a long term (four weeks) at 22ºC under a 16/8-h (day/night) photoperiod. After the long term cultivation, enrichment of 18O in the flavonoid aglycones has been confirmed by LC-Orbitrap-MS analysis. On the other hand, no detectable 18O has been found in all metabolites from P. patens grown with molecular 18O2 for four weeks at 22ºC under continuous light condition. We will discuss the MS/MS analysis of the 18O labeled metabolites.
