Comparison of the phospholipid requirements and molecular form of CTP: Phosphocholine cytidylyltransferase from rat lung, kidney, brain and liver

The Cytidylyltransferase activity in fresh cytosol from different tissues of the rat was measured in the absence and presence of phosphatidylglycerol. In all cases addition of this lipid produced large increases in enzyme activity. Agarose gel (A-5.0) filtration profiles of the enzyme activities indicated that the L-form of the enzyme (190000 molecular weight) predominated in liver, brain, kidney, and fetal lung. However, adult lung cytosol contained 70–80% of the activity in the H-form (molecular weight ⩾ 5 · 106). Removal of phospholipid material from the alveolar spaces by lavage produced a significant reduction of the H-form of the enzyme in the cytosol fraction. The L-form of the cytidylyl-transferases from fetal lung and adult liver, kidney, and brain all possess the same specificities for activation by phospholipids in vitro. In all cases, phosphatidylglycerol was the most potent activator at 0.2 mM. Lysophosphatidylethanolamine stimulated enzyme activity, whereas lysophosphatidylglycerol was a potent inhibitor. These studies implicate the role of acidic phospholipids in the regulation of cytidylyltransferase activity in vivo and the existence of a common L-form of the enzyme in several tissues of the rat.