Angular stomatitis and cracked lips are caused by deficiency of

A tetrapeptide is formed from four amino acids: alanine, serine, glycine, and valine. The C-terminal is fixed as alanine, and the N-terminal amino acid is chiral. Determine the number of possible sequences.

Cheilosis and digestive disorders are due to deficiency of

A tetrapeptide is made of naturally occuring alanine, serine, glycine and valine. If the $ C $-terminal amino acid is alanine and N-terminal amino acid is chiral, the number of possible sequence of the tetrapeptide is