REVERSIBLE TRANSLOCATION OF CTP-PHOSPHOCHOLINE CYTIDYLYLTRANSFERASE FROM CYTOSOL TO MEMBRANES IN THE ADULT BOVINE LIVER AROUND PARTURITION

The key regulatory enzyme of phosphatidylcholine (PC) synthesis, CTP:p hosphocholine cytidylyltransferase (CT), is known to be activated in v itro by translocation from soluble to particulate fractions of the cel l. In the present study the periparturient cow was chosen as a model t o investigate whether translocation of CT can contribute to the regula tion of PC synthesis in vivo. Between parturition and 1.5 weeks post-p artum, the cytosolic CT activity in the liver of the adult animal decr eased 1.9-fold, and this correlated with a 1.8-fold increase in micros omal CT activity. At that time, microsomal CT activity started to decl ine again whereas the cytosolic activity rose concomitantly until both activities reached their pre-partum values at 8 weeks post-partum The activities of soluble and membrane-bound CTP:phosphoethanolamine cyti dylyltransferase (ET), the analogous enzyme in the CDP-ethanolamine pa thway, did not change significantly throughout this period. Whereas he patic FC concentrations declined until about 2 weeks post-partum and t hereafter gradually returned to pre-partum levels, the PC levels in ve ry-low-density-lipoproteins, started to rise 2 weeks after the partus reaching a maximum of 219% of the original value at 8 weeks post-partu m. These results strongly suggest that there is a reversible membranes in a physiologically relevant animal model, supporting the concept th at translocation of CT is occurring in vivo. (C) 1998 Elsevier Science B.V.