The N-acylpeptide hydrolase from porcine intestine: isolation, subcellular localization and comparative hydrolysis of peptide and isopeptide bonds.

The N-acylpeptide hydrolase from porcine intestinal mucosa was 2000-fold purified by a five-step procedure. The resulting protein (about 300 kDa) is composed of four apparently identical N-acylated polypeptide chains. The enzyme activity was found to be equally distributed along the crypt-villus axis in the intestine and was characterized as a cytosolic protein. Besides the ability of porcine intestinal APH to cleave the first peptide bond in N-protected peptides (Km: 0.8 mM), it is worth stressing that the enzyme was also found to efficiently catalyze the hydrolysis of the isopeptide bond in N-epsilon-Ac-L-Met-L-Lys (Km: 0.7-1.1 mM). It is suggested that N-acylpeptide hydrolase might not only be involved in the catabolism of intracellular N-acylated protein catabolism but also be responsible for the biological utilization of N-acylated food proteins.