Amino acid "X" represents synthetic molecules or molecules that are unidentified or unknown.
Amino acids are known by there full names, their 3 letter abbreviation, and their 1 letter abbreviations. For example, a proline amino acid is known as "Proline", "Pro", or just "P". For our alphabet, we use the one letter abbreviation. Many of customers use this amino acid bead alphabet to spell messages, names, or initials. For instance, a girl named "Anna" can spell her name using the amino acids: Alanine (A) and Asparagine (N).