PCMT1, also known as L-isoaspartyl protein carboxyl methyltransferase, is an enzyme that catalyses the methyl esterification of L-isoaspartyl and D-aspartyl residues in peptides and proteins that result from spontaneous decomposition of normal L-aspartyl and L-asparaginyl residues. This protein plays a role in the repair and/or degradation of damaged proteins.