title: Protein NH2-terminal asparagine deamidase. Isolation and characterization of a new enzyme.
abstract: An apparently unique enzyme, designated protein NH2-terminal asparagine deamidase (PNAD), that specifically converts NH2-terminal asparagine residues of peptide and protein substrates to aspartic acid, has been isolated to homogeneity from porcine liver by an eight-step procedure. PNAD is a relatively low abundance protein, is readily solubilized, and exists as a monomeric species of approximately 33 kDa. PNAD does not act on internal asparagine residues and requires a free N alpha-amino group. It has reduced or no activity on NH2-terminal asparagine dipeptides and no activity toward free asparagine or asparagine amide. It does not act on any NH2-terminal glutamine substrates. PNAD does not show a strong pH dependence suggesting that the enzyme can act equally well on substrates with ionized or unionized alpha-amino groups. The properties and specificity of PNAD are consistent with those expected for the enzyme required for the ubiquitin-dependent turnover of intracellular proteins that initiate with Met-Asn-. Such proteins should be N alpha-acetylated on the retained initiator methionine and can subsequently be modified by the removal of N-acetyl methionine by acylaminoacid hydrolase. Conversion of the resulting NH2-terminal asparagine to aspartic acid by PNAD would render the protein susceptible to arginylation, polyubiquitinylation and degradation as specified by the N-end rule.
authors.affiliation: Department of Biological Chemistry, College of Medicine, University of California, Irvine 92717.
authors.forename: A E
authors.initials: AE
authors.lastname: Stewart
authors.forename: S M
authors.initials: SM
authors.lastname: Arfin
authors.forename: R A
authors.initials: RA
authors.lastname: Bradshaw
mesh_terms: D000581:Amidohydrolases / Q000302:isolation & purification* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001216:Asparagine / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D013379:Substrate Specificity; D013552:Swine
chemical_list: D010455:Peptides; D001216:Asparagine; D000581:Amidohydrolases; C089503:protein NH2-terminal asparagine deamidase