3-beta-D-Galactosyl-1,2-diacylglycerol mono-beta-D-galactosyldiacyl glycerol beta-D-galactosyltransferase (n-C18 4)
2.0 mgdg184_6_9_12_15_c ⇌ dgdg184_6_9_12_15_c + 12dgr184_6_9_12_15_c