ACETYL-COA CARBOXYLASE - EVIDENCE FOR POLYMERIC FILAMENT TO PROTOMER TRANSITION IN INTACT AVIAN LIVER-CELL

Google Scholar
  • 1 January 1978
    • journal article
    • research article
    • Vol. 253  (10) , 3381-3383
Abstract
Digitonin treatment of chick liver cells in monolayer culture perforates the plasma membrane, causing release of acetyl-CoA carboxylase [EC 6.4.1.2] and other cytosolic enzymes. The rate of carboxylase release is affected by conditions known to alter the position of the protomer-polymer (filament) equilibrium of the enzyme. Citrate, an allosteric activator of the carboxylase, induces polymerization of the protomeric avidin-sensitive form giving rise to the avidin-insensitive polymeric filamentous form. When cells are exposed to N6,O2-dibutyryl cyclic AMP which lowers intracellular citrate levels, the rate of carboxylase release from digitonin-treated cells is greatly accelerated. The presence of avidin, which rapidly enters the cell during digitonin treatment, inactivates carboxylase under conditions that promote depolymerization and rapid release, but not under conditions which promote polymerization and slow release. Carboxylase filaments exist in the intact chick liver cell when the cytoplasmic citrate level is high and undergo depolymerization when citrate levels fall.