The amino acid which is basic in nature is

$A$ tetrapeptide $x$ on complete hydrolysis produced glycine $(Gly)$,alanine $(Ala)$,valine $(Val)$,and leucine $(Leu)$ in equimolar proportions. The number of possible tetrapeptide sequences involving each of these amino acids exactly once is:

Leucine amino acid is:

At the isoelectric point:

Which of the following tests cannot be used for identifying amino acids?

$\beta-$pleated sheets of polypeptide chains are present in