The answer depends on the two sequences. If the two sequences are identical, then there would be 0 different amino acids between them. If the two sequences differ by one amino acid, then there would be 1 different amino acid between them. If the two sequences differ by two amino acids, then there would be 2 different amino acids between them. If the two sequences differ by three or more amino acids, then there would be 3 or more different amino acids between them.
