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.

Immunological analysis of porin polymorphism in Escherichia coli B and K-12.

Two sets of monoclonal antibodies (MoF type I and MoF type II) directed against the OmpF protein were used to analyze the immunological reactivity of the major outer membrane porins of E. coli B and K-12. All these antibodies present a specificity to the native OmpF protein. In addition, among the type II antibodies, MoF 18, 19 and 20 could recognize an epitope present on both monomeric and trimeric forms of the porin as demonstrated by immunoblotting analyses. The use of two different screening methods led to the isolation of two different sets of MoF, one specific for a native conformation accessible only on E. coli B strain and the second directed against epitopes present on OmpF of the two strains, B and K-12. These various responses are discussed in relation to the lipopolysaccharide binding to OmpF and with respect to the screening test used.