Pathways

Phosphatidylcholines (PC) are a class of phospholipids that incorporate a phosphocholine headgroup into a diacylglycerol backbone. They are the most abundant phospholipid in eukaryotic cell membranes and has both structural and signalling roles. In eukaryotes, there exist two phosphatidylcholine biosynthesis pathways: the Kennedy pathway and the methylation pathway. The Kennedy pathway begins with the direct phosphorylation of free choline into phosphocholine followed by conversion into CDP-choline and subsequently phosphatidylcholine. It is the major synthesis route in animals. The methylation pathway involves the 3 successive methylations of phosphatidylethanolamine to form phosphatidylcholine. The first reaction of the Kennedy pathway involves the cytosol-localized enzyme choline/ethanolamine kinase catalyzing the conversion of choline into phosphocholine. Second, choline-phosphate cytidylyltransferase, localized to the endoplasmic reticulum membrane, catalyzes the conversion of phosphocholine to CDP-choline. Last, choline/ethanolaminephosphotransferase catalyzes phosphatidylcholine biosynthesis from CDP-choline. It requires either magnesium or manganese ions as cofactors. A parallel Kennedy pathway forms phosphatidylethanolamine from ethanolamine - the only difference being a different enzyme, ethanolamine-phosphate cytidylyltransferase, catalyzing the second step. Phosphatidylethanolamine is also synthesized from phosphatidylserine in the mitochondrial membrane by phosphatidylserine decarboxylase. Phosphatidylethanolamine funnels into the methylation pathway in which phosphatidylethanolamine N-methyltransferase (PEMT) then catalyzes three sequential N-methylation steps to convert phosphatidylethanolamine to phosphatidylcholine. PEMT uses S-adenosyl-L-methionine as a methyl donor.

Phosphatidyl ethanolamine reacts with S-adenosylmethionine through a phosphatdylethanolamine N-methyltransferase resulting in the release of hydrogen ion and S-adenosylhomocysteine an a PE-NMe. The PE-NMe reacts with S'-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resulting in the release of hydrogen ion, s-adenosylhomocysteine and PE-NMe2. The PE-NMe2 reacts with s-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resuilting in the release of hydrogen ion, s-adenosylhomocysteine and PC

Phosphatidyl ethanolamine reacts with S-adenosylmethionine through a phosphatdylethanolamine N-methyltransferase resulting in the release of hydrogen ion and S-adenosylhomocysteine an a PE-NMe. The PE-NMe reacts with S'-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resulting in the release of hydrogen ion, s-adenosylhomocysteine and PE-NMe2. The PE-NMe2 reacts with s-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resuilting in the release of hydrogen ion, s-adenosylhomocysteine and PC

Phosphatidyl ethanolamine reacts with S-adenosylmethionine through a phosphatdylethanolamine N-methyltransferase resulting in the release of hydrogen ion and S-adenosylhomocysteine an a PE-NMe. The PE-NMe reacts with S'-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resulting in the release of hydrogen ion, s-adenosylhomocysteine and PE-NMe2. The PE-NMe2 reacts with s-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resuilting in the release of hydrogen ion, s-adenosylhomocysteine and PC

Phosphatidyl ethanolamine reacts with S-adenosylmethionine through a phosphatdylethanolamine N-methyltransferase resulting in the release of hydrogen ion and S-adenosylhomocysteine an a PE-NMe. The PE-NMe reacts with S'-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resulting in the release of hydrogen ion, s-adenosylhomocysteine and PE-NMe2. The PE-NMe2 reacts with s-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resuilting in the release of hydrogen ion, s-adenosylhomocysteine and PC

Phosphatidyl ethanolamine reacts with S-adenosylmethionine through a phosphatdylethanolamine N-methyltransferase resulting in the release of hydrogen ion and S-adenosylhomocysteine an a PE-NMe. The PE-NMe reacts with S'-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resulting in the release of hydrogen ion, s-adenosylhomocysteine and PE-NMe2. The PE-NMe2 reacts with s-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resuilting in the release of hydrogen ion, s-adenosylhomocysteine and PC

Phosphatidyl ethanolamine reacts with S-adenosylmethionine through a phosphatdylethanolamine N-methyltransferase resulting in the release of hydrogen ion and S-adenosylhomocysteine an a PE-NMe. The PE-NMe reacts with S'-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resulting in the release of hydrogen ion, s-adenosylhomocysteine and PE-NMe2. The PE-NMe2 reacts with s-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resuilting in the release of hydrogen ion, s-adenosylhomocysteine and PC

Phosphatidyl ethanolamine reacts with S-adenosylmethionine through a phosphatdylethanolamine N-methyltransferase resulting in the release of hydrogen ion and S-adenosylhomocysteine an a PE-NMe. The PE-NMe reacts with S'-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resulting in the release of hydrogen ion, s-adenosylhomocysteine and PE-NMe2. The PE-NMe2 reacts with s-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resuilting in the release of hydrogen ion, s-adenosylhomocysteine and PC

Phosphatidyl ethanolamine reacts with S-adenosylmethionine through a phosphatdylethanolamine N-methyltransferase resulting in the release of hydrogen ion and S-adenosylhomocysteine an a PE-NMe. The PE-NMe reacts with S'-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resulting in the release of hydrogen ion, s-adenosylhomocysteine and PE-NMe2. The PE-NMe2 reacts with s-adenosylmethionine through a phosphotidyl-N-methylethanolamine N-methyltransferase resuilting in the release of hydrogen ion, s-adenosylhomocysteine and PC

Phosphatidylcholines (PC) are a class of phospholipids that incorporate a phosphocholine headgroup into a diacylglycerol backbone. They are the most abundant phospholipid in eukaryotic cell membranes and has both structural and signalling roles. In eukaryotes, there exist two phosphatidylcholine biosynthesis pathways: the Kennedy pathway and the methylation pathway. The Kennedy pathway begins with the direct phosphorylation of free choline into phosphocholine followed by conversion into CDP-choline and subsequently phosphatidylcholine. It is the major synthesis route in animals. The methylation pathway involves the 3 successive methylations of phosphatidylethanolamine to form phosphatidylcholine. The first reaction of the Kennedy pathway involves the cytosol-localized enzyme choline/ethanolamine kinase catalyzing the conversion of choline into phosphocholine. Second, choline-phosphate cytidylyltransferase, localized to the endoplasmic reticulum membrane, catalyzes the conversion of phosphocholine to CDP-choline. Last, choline/ethanolaminephosphotransferase catalyzes phosphatidylcholine biosynthesis from CDP-choline. It requires either magnesium or manganese ions as cofactors. A parallel Kennedy pathway forms phosphatidylethanolamine from ethanolamine - the only difference being a different enzyme, ethanolamine-phosphate cytidylyltransferase, catalyzing the second step. Phosphatidylethanolamine is also synthesized from phosphatidylserine in the mitochondrial membrane by phosphatidylserine decarboxylase. Phosphatidylethanolamine funnels into the methylation pathway in which phosphatidylethanolamine N-methyltransferase (PEMT) then catalyzes three sequential N-methylation steps to convert phosphatidylethanolamine to phosphatidylcholine. PEMT uses S-adenosyl-L-methionine as a methyl donor.