Dual modulation of hepatic and intestinal acyl-CoA: cholesterol acyltransferase activity by (de-)phosphorylation and substrate supply in vitro.

Acyl-CoA: cholesterol acyltransferase (ACAT) activity in microsomes from rat liver and rat intestinal epithelial cells was increased by incubation of the microsomes with the 100 000 x g supernatant fraction in the presence of ATP/MgCl2 and NaF. The measured activity was further increased by including cholesterol-rich liposomes in the preincubation. The ACAT activity in rat liver microsomes could be inhibited by preincubation in the presence of 100 000 x g supernatant and MgCl2 and microsomes preactivated by ATP/MgCl2 could also be inhibited in this way. The results suggest that ACAT activity in vitro is modulated by substrate supply and also reversibly by an ATP-dependent process which may be protein phosphorylation.