Catalyzes the transfer of the malonyl group from malonyl-CoA to the 4'''-hydroxyl group of the 5-glucosyl moiety of anthocyanins. Anthocyanins are ubiquitous colored pigments that are responsible for petal color. 4'''-demalonylsalvianin + malonyl-CoA = CoA + salvianin Inhibited by the following metal ions: Cd(2+), Cu(2+), Fe(2+), Hg(2+) and Zn(2+). Activity is strongly inhibited by CoA-SH and partially inhibited by acetyl-CoA, caffeic acid and bisdemalonylsalvianin. kcat is 0.55 sec(-1) (with native enzyme). kcat is 0.76 sec(-1) (with recombinant enzyme). Pigment biosynthesis; anthocyanin biosynthesis. Monomer. Expressed at higher level in recently opened, fully pigmented flowers. Belongs to the plant acyltransferase family.