Involved in the malonylation of the 5-O-glucose residue of anthocyanin. Acts only on anthocyanin substrates containing a 5-O glucosyl moiety. Not able to catalyze acyl transfer using acetyl-CoA, butyryl-CoA, hexanoyl- CoA, benzoyl-CoA, cinnamoyl-CoA, methylmalonyl-CoA, succinyl-CoA, p-coumaroyl-CoA or caffeoyl-CoA. kcat is 0.02 sec(-1) for cyanin. kcat is 1.79 sec(-1) for malvin. kcat is 0.12 sec(-1) for cyanidin 3-O-[2''-O-(xylosyl)-6''-O-(p-O-(glucosyl)-p-coumaroyl) glucoside]5-O-glucoside. kcat is 0.00012 sec(-1) for cyanidin 3-O-[2''-O-(2'''-O-(sinapoyl) xylosyl)6''-O-(p-O-(glucosyl) p-coumaroyl) glucoside]5-O-glucosid. kcat is 6.4 sec(-1) for cyanidin 3,5-diglucoside. kcat is 5.9 sec(-1) for pelargonidine 3,5-diglucoside. kcat is 6.6 sec(-1) for peonidine 3,5-diglucoside. kcat is 0.2 sec(-1) for malonyl-CoA (with cyanidin 3-O-[2''-O-(xylosyl)-6''-O-(p-O-(glucosyl)-p-coumaroyl) glucoside]5-O-glucoside as cosubstrate). kcat is 0.0013 sec(-1) for malonyl-CoA (with cyanidin 3-O-[2''-O-(2'''-O-(sinapoyl) xylosyl)6''-O-(p-O-(glucosyl) p-coumaroyl) glucoside]5-O-glucoside as cosubstrate). kcat is 6.4 sec(-1) for malonyl-CoA (with cyanidin 3,5-diglucoside as cosubstrate). Optimum pH is 6.0-7.5. Expressed in flowers. Detected in leaves, stems, roots and siliques. Up-regulated by high sucrose and by low phosphate stresses. Absence of malonyl-modified anthocyanins. Belongs to the plant acyltransferase family.