Christy, M. Robert; Barkley, Robert M.; Koch, Tad H.; Van Buskirk, John J.; Kirsch, Wolff M. (1981). «The new amino acid .beta.-carboxyaspartic acid (asa). Laboratory synthesis and identification in the ribosomal proteins of E. coli». Journal of the American Chemical Society (American Chemical Society (ACS)) 103 (13): 3935–3937. doi:10.1021/ja00403a060. ISSN0002-7863.
Christy, M. Robert; Barkley, Robert M.; Koch, Tad H.; Van Buskirk, John J.; Kirsch, Wolff M. (1981). «The new amino acid .beta.-carboxyaspartic acid (asa). Laboratory synthesis and identification in the ribosomal proteins of E. coli». Journal of the American Chemical Society (American Chemical Society (ACS)) 103 (13): 3935–3937. doi:10.1021/ja00403a060. ISSN0002-7863.