ABSTRACT
Regulation of metabolic flux, by variation in the amount of active enzyme, is a common mechanism used by cells to control the biosynthesis of important cellular components. The coincidence of the increase in cytidylyltransferase (CT) activity on microsomes and an increased rate of PC synthesis in liver provides another in vivo model system which suggests CT translocation is a physiologically important mechanism for control of phosphatidylcholine (PC) biosynthesis. The effects of hormones on PC biosynthesis have been investigated in several systems. PC biosynthesis is regulated at the level of gene expression in selected cases. PC biosynthesis can occur in several organelles in animal cells, but the major quantitative site is the endoplasmic reticulum. The secretion of other proteins from the liver cells did not seem to be affected by reduced PC biosynthesis. Scientists have suspected for many years that PC is essential for cell viability.
