3-beta-D-Galactosyl-1,2-diacylglycerol mono-beta-D-galactosyldiacyl glycerol beta-D-galactosyltransferase (n-C18 3)
2.0 mgdg183_9_12_15_c ⇌ dgdg183_9_12_15_c + 12dgr183_9_12_15_c