Enables protein-L-isoaspartate (D-aspartate) O-methyltransferase activity. Acts upstream of or within regulation of calcium-mediated signaling. Predicted to be located in cytosol and membrane. Predicted to be active in cytoplasm. Is expressed in brain; heart; liver; and pleuroperitoneal region. Orthologous to human PCMT1 (protein-L-isoaspartate (D-aspartate) O-methyltransferase).