[Isoform 1]: Catalyzes the key rate-limiting step in the CDP- choline pathway for phosphatidylcholine biosynthesis. . [Isoform 2]: Catalyzes the key rate-limiting step in the CDP- choline pathway for phosphatidylcholine biosynthesis. . This is the function of PCYT1B (phosphate cytidylyltransferase 1B, choline, Ensembl gene identifier ENSG00000102230).