D-Amino-acid racemase, a PLP-dependent enzyme, racemizes amino acids via the formation of the alpha-iminoacids, where the stereogenic center is lost. L-amino-acid oxidases convert L-amino acids to the alpha-ketoacids, which are susceptible to reductive amination. Some amino acids are prone to racemization, one example being lysine, which racemizes via formation of pipecolic acid.