Three varieties of methyl citrate and 1-methyl malate were isolated from th
e fruits of Opuntia ficus-indica var. saboten Makino through in vitro bioas
say-guided isolation for the inhibition on monoamine oxidase(MAO). The IC50
values for MAO-B of l-monomethyl citrate, 1,3-dimethyl citrate, trimethyl
citrate and 1-methyl malate were 0.19, 0.23, 0.61 and 0.25 mM, respectively
. However, on MAO-A, their inhibitions showed only marginal activity.