n h 2
0 — P — o — lj>— o — CH
F IG U R E 1 9 -2
Synthesis of phosphatidylcholine. The rate-limiting reaction is that catalyzed by cytidylyltransferase (reaction 2) which
appears to be active only when attached to the endoplasmic reticulum, although it is also found free in the cytosol.
Cytidylyltransferase is inactivated by a cAMP-dependent protein kinase and activated by a phosphatase. Translocation
to the endoplasmic reticulum can be stimulated by substrates such as fatty acyl Coenzyme A (CoA). Choline deficiency
can result in deposition of triacylglycerol in liver and reduced phospholipid synthesis. Enzymes: (1) choline kinase;
(2) CTP:phosphocholine cytidylyltransferase; (3) glycerol kinase; (4) acyl-CoA: glycerol-3-phosphate acyltransferase;
(5) acyl-CoA: acyl glycerol-3-phosphate acyltransferase; (
) phosphatidic acid phosphatase; (7) CDP-choline:
diacylglycérol phosphocholine transferase.