Acid lipase and acid cholesterol esterase (CEase) in rat arterial wall were largely associated with lysosomal fraction. Then lysosomal fraction of arterial wall was preincubated with 0.04% Triton-X 100 for 5min. at 0°C. Acid lipase and acid CEase were released from lysosomal fraction. The released lipase and CEase were more inactivated than those associated with lysosomal fraction, when they were preincubated for 10min. at 37°C.
When lysosomal fraction was treated with various concentration of Triton-X 100 for 5min at 0°C and centrifuged, acid lipase was released from lysosome in a small amount than acid CEase. From these results, the relationship between stability of lysosomal enzyme activities and lipid accumulation in lysosome was discussed.
Higher activity of lipase was observed using sonicated substrate than one homogenated with a Hiscotron (Nichion, Japan). High activity was observed when substrate mixed with phosphatidylcholine and arabic gum was sonicated. Lipase activity was elevated by an addition of 0.25mM phospholipid especially phosphatidylserine and phosphatidylcholine to reaction mixture, and was lowered by an addition of 2mM or more dosage of those phospholipids. It is suggested that phospholipids might be an important regulatory factor of lipase activity in the arterial wall.
We reported that serum nonspecific catboxyl esterase (tributyline hydrolase) might be converted to lipase (triolein hydrolase) in aorta. Further study has been done using lysosomal fraction of the arterial wall. Purified serum esterase was incubated with lysosomal fraction which was pretreated with heparin to remove lipase. Elevation of acid lipase activity was observed. But when boiled esterase was incubated with it, no elevation of lipase activity was observed. These results suggested that serum nonspecific carboxyl esterase might be converted to lipase in lysosome of aorta. Further studies were now in progress to certify this possibility.