MECHANISM OF PHOSPHORYLATION IN THE LUMEN OF THE GOLGI-APPARATUS - TRANSLOCATION OF ADENOSINE 5'-TRIPHOSPHATE INTO GOLGI VESICLES FROM RAT-LIVER AND MAMMARY-GLAND

  • 25 March 1989
    • journal article
    • research article
    • Vol. 264  (9) , 5233-5240
Abstract
The occurrence of phosphorylated secretory proteins such as caseins and vitellogenin and the recent characterization of phosphorylated proteoglycans, in the xylose and protein core, has raised the question of where in the cell and how this phosphorylation occurs. Previous studies have described a casein kinase activity in the lumen of the Golgi apparatus and this organelle as the site of xylose addition to the protein core of proteoglycans. We now report the translocation in vitro of ATP into the lumen of rat liver and mammary gland Golgi veiscles which are sealed and have the same membrane topographical orientation as in vivo. The entire ATP molecule was translocated into the lumen of the Golgi vesicles; this was established by using ATP radiolabeled with tritium in the adenine and .gamma.-32P. Translocation was temperature dependent and saturable, with an apparent Km of 0.9 .mu.M and Vmax of 58 pmol/mg protein/min. Preliminary evidence suggest that translocation fo ATP into the vesicles'' lumen is coupled to exit of AMP from the lumen. Following translocation of ATP into the lumen of the vesicles, proteins were phosphorylated.