An element essential for nitrogen metabolism is

The conversion of $NO_{3}^{-} \rightarrow NO_{2}^{-} \rightarrow NH_{3}$ is called and is catalysed by:

Complete the equation.
$\alpha -$ Ketoglutaric acid $+ NH_4^+ +$ ...$A$.... $\xrightarrow[\text{Dehydrogenase}]{\text{glutamate}} $ ...$B$... $+ H_2O + NADP$
Identify $A$ and $B$.

Amino acids are mostly synthesised from

The amino acid which plays a central role in nitrogen metabolism is/are:

Complete the equation for reductive amination.