The metabolism of glyceride glycolipids. IV. Enzymatic hydrolysis of monogalactosyl and digalactosyl diglycerides in rat brain.

Particulate fractions of rat brain catalyze the hydrolysis of radiochemically pure monogalactosyl and digalactosyl diglycerides, which had been synthesized in vifro by enzymes derived from rat brain or spinach chloroplasts. Monogalactosyl-U-W diglyceride (the galactose being uniformly labeled) yields W-galactose when incubated with the mitochondrial fraction of brain at the optimum pH of 4.4 (galactosidase conditions) and monogalactosyl-UJ4C glycerol when incubated with the microsomal fraction of brain at the optimum pH of 7.2 (galactolipase conditions). Biosynthesized digalactosyl-U-14C diglyceride is degraded in a similar way. There is no cross-contamination of the two degradative enzyme systems. Studies of activity plotted against age reveal that the galactolipase activity with either monogalactosyl or digalactosyl diglyceride as substrate increases with age (up to at least 40 days) except during the period of most active myelination (approximately 10 to 20 days of age), at which time the galactolipase activity is notably depressed.