Journal of Lipid Research, Vol. 10, 623-630, November 1969
Copyright © 1969 by Lipid Research, Inc.
Biosynthesis of galactolipids by enzyme preparations from spinach leaves
J. B. Mudd , H. H. D. M. Van Vliet , and L. L. M. Van Deenen
Laboratory of Biochemistry, University of Utrecht, Utrecht, The Netherlands
The pH optimum for galactolipid synthesis from UDP-galactose by spinach chloroplasts is 7.2 in Tris-HCl or phosphate buffer. The products include sterol glycosides, trigalactosyl diglyceride (tentatively identified), digalactosyl diglyceride, and monogalactosyl diglyceride in increasing order of quantity. The proportion of monogalactosyl diglyceride decreases and that of digalactosyl diglyceride increases as the pH is lowered. The galactolipid synthesis is quite resistant to elevated temperature; maximal incorporation of galactose from UDP-galactose was observed at 45°C. The proportion of monogalactosyl diglyceride was greater at the higher temperatures. As much as 40% of the galactolipid-synthesizing capability of a spinach leaf homogenate is not sedimented by centrifugation for 60 min at 100,000 g.
An acetone powder of spinach chloroplasts contains enzymes which catalyze galactolipid synthesis. This preparation is dependent on added diglycerides in order to make galactolipid, whereas the chloroplast preparation is not dependent on added diglycerides. Molecular species of diglycerides were compared as requirements for galactolipid synthesis. The requirement was satisfied best by the diglycerides of highest unsaturation. Methylation of the free hydroxyl of the diglyceride eliminated the effectiveness.
Supplementary key words diglyceride molecular species • chloroplasts • subcellular distribution • UDP-galactose • fatty acid composition
Submitted on May 12, 1969
Accepted on July 8, 1969
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