Amino acid polymorphisms of the human L-isoaspartyl/D-aspartyl methyltransferase involved in protein repair.

We have analyzed DNA from three exons of the human protein-L-isoaspartate(D-aspartate) O-methyltransferase gene in 30 individuals. We present evidence for two polymorphisms in these regions that result in amino acid changes. At a site corresponding to amino acid position 119, we find the ATA codon for Ile at a frequency of 0.77 and the GTA codon for Val at a frequency of 0.23. At the site corresponding to amino acid position 205, we find the AAG codon for Lys at a frequency of 0.98 and the AGG codon for Arg at a frequency of 0.02. These amino acid changes may affect the ability of this enzyme to recognize and catalyze the first step in the repair of proteins spontaneously damaged in the aging process.