Component of the oleanane-type triterpene saponins (e.g. ginsenosides or panaxosides) biosynthetic pathway (PubMed:29378087). Catalyzes the carboxylation of beta-amyrin at the C-28 position to form oleanolic acid during ginsenoside biosynthesis, a class of tetracyclic triterpenoid saponins. beta-amyrin + 3 O2 + 3 reduced [NADPH--hemoprotein reductase] = 4 H(+) + 4 H2O + oleanolate + 3 oxidized [NADPH--hemoprotein reductase] Secondary metabolite biosynthesis; terpenoid biosynthesis. Mostly expressed in roots, and, to a lower extent, in stems and leaves (PubMed:30577538). Accumulates only in the rhizome of plants (PubMed:22875608). Progressive increase in roots from the leaf opened stage to the green fruit, red fruit and root growth stages, respectively. Expression is not affected by methyl jasmonate (MeJA) treatment (PubMed:22875608). Influenced in roots and leaves by relative humidity and soil water potential (PubMed:30577538). Belongs to the cytochrome P450 family.