Galactosyltransferase Activities in Intact Spinach Chloroplasts and Envelope Membrane Involvement of Galactolipid: Galactolipid Galactosyltransferase

Digalactosyldiacylglycerol (DGDG) is a major lipid of the chloroplast membranes (1). in our studies to the galactolipid synthesis in isolated chloroplast envelopes membrane, we could measure only one enzymatic activity involved in DGDG synthesis: galactolipid: galactolipid galactosyltransferase (GGGT). We were unable to measure an alternative reaction involving an UDPGal: monogalactosyldiacylglycerol galactosyl-transferase (2–4). However, apart from DGDG, GGGT produces diacylglycerol and the higher homologues tri- and tetragalactocyldiacylglycerol (TGDG and TeGDG): $$ \begin{array}{*{20}{c}} {MGDG + MGDG \to DGDG + diacy\lg lycerol}\\ {DGDG + MGDG \to TGDG + diacy\lg lycerol.} \end{array} $$