Abstract
Phospholipase C markedly reduced the ATPase activity of microsomes isolated from gastric mucosa of rabbit or bullfrog. After such treatment the ATPase enzyme remained in the particulate fraction and was not released into the supernatant. Synthetic lecithin (dipalmitoyl) restored a large fraction of the ATPase activity in microsomes pretreated with phospholipase C, whereas cephalin (dipalmitoyl) was without effect. Analysis of lipid constituents of the gastric microsomes after vigorous extraction procedures showed large quantities of lecithin, cephalin and cholesterol. Extraction of the microsomal membranes with ether removed only the more neutral lipids and did not alter the ATPase activity of the preparation. Electron microscopic oxservations of negatively stained gastric microsomes revealed them to be tubular structures, morphologically similar to elements of the smooth-surfaced endoplasmic reticulum of acid secreting cells. After treatment with phospholipase C a structural degradation of the gastric microsomal membranes occurs; the formerly smooth surfaces become rough and irregular. A conformational change in the proteinaceous ATPase, as a result of destruction of specific phospholipid attachment sites, is suggested as the mechanism for the observed changes in enzymic activity.
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