– Human protein N-terminal glutamine amidohydrolase (WDYHV1) is an enzyme that in humans is encoded by the WDYHV1 gene, belongs to the NTAQ1 family.WDYHV1 mediates the side-chain deamidation of N-terminal glutamine residues to glutamate, which is an important step in N-end rule pathway of protein degradation. Conversion of the resulting N-terminal glutamine to glutamate renders the protein susceptible to arginylation, polyubiquitination and degradation as specified by the N-end rule. However,it does not act on substrates with internal or C-terminal glutamine andnon-glutamine residues in any position. With the exception of proline, all tested second-position residues on substrate peptides do not greatly influence the activity. In contrast, a proline at position 2, virtually abolishes deamidation of N-terminal glutamine.