A peptidyl dipeptidase-4 from Pseudomonas maltophilia: purification and properties

New Insights into the Proteolytic System of Streptococcus thermophilus: Use of Isracidin To Characterize Cell-Associated Extracellular Peptidase Activities

The influence on the hydrolysis of isracidin of cell-associated extracellular aminopeptidase and X-prolyl dipeptidyl peptidase activities in addition to protease PrtS of Streptococcus thermophilus strains was investigated. S. thermophilus LMD-9 (PrtS(+) phenotype) efficiently hydrolyzed the isracidin mainly through the PrtS activity, whereas strain CNRZ1066 (PrtS(-) phenotype) and two mutant strains LMD-9-ΔprtS and LMD-9-ΔprtS-ΔhtrA also displayed substrate hydrolysis, but different from that of the wild type strain LMD-9. Identification by mass spectrometry of breakdown products of isracidin revealed the existence of novel cell-associated extracellular carboxypeptidase and peptidyl dipeptidase activities in all PrtS(-) strains, besides known cell-associated extracellular aminopeptidase and X-prolyl dipeptidyl peptidase activities. Both aminopeptidase and peptidyl dipeptidase activities were not able to cleave the isracidin at peptide bonds with proline residues. No hydrolysis of isracidin was detected in cell free filtrate for all the strains studied, indicating that no cell lysis had occurred. Taken together, these results suggested the presence of cell-associated extracellular peptidase activities in S. thermophilus strains that could be vital for the growth of PrtS(-) strains.

Some molecular and inhibitory specifications of a dipeptidyl carboxypeptidase from the polychaete Neanthes virens resembling angiotensin I converting enzyme

Dipeptidyl carboxypeptidase (DCP) from the polychaete Neanthes virens, resembling mammalian angiotensin I converting enzyme (ACE), was studied to discover some of its molecular and inhibitory properties, as the first evidence of these in a marine invertebrate. Amino acid and carbohydrate contents were analyzed. The N-terminal amino acid sequence of N. virens DCP was (NH2)D-E-E-A-G-R-Q-W-L-A-E-Y-D-L-R-N-Q-T-V-L-. Peptide maps of N. virens DCP from lysyl endopeptidase digestion were different from rabbit p-ACE. The far-ultraviolet circular dichroic spectra of N. virens DCP indicated that the secondary structure of this enzyme seemed to be an alpha-helical structure and was similar to that of rabbit p-ACE, but the near-ultraviolet circular dichroic spectra of N. virens DCP indicated that the aromatic amino acid residue circumambience of this enzyme was different from rabbit p-ACE. The effects of several reagents for chemical modification of amino acids on the activity of N. virens DCP were tested. Arg, Tyr, Glu, and/or Asp, His, Trp, and Met caused loss of the activity. In addition, the IC50 and Ki values for a well-known ACE inhibitor, Val-Tyr, which was a competitive inhibitor of N. virens DCP, were 263 and 20 microM, respectively. These results suggested that N. virens DCP is different from mammalian ACE in the molecular and inhibitory properties, although the same substrate specificity was demonstrated in a previous paper.

Purification and characterization of a dipeptidyl carboxypeptidase from the polychaete Neanthes virens resembling angiotensin I converting enzyme

Dipeptidyl carboxypeptidase (DCP) is well known as a mammalian angiotensin I converting enzyme (ACE) which plays an important role in blood pressure homeostasis. DCP was purified from the whole body of a polychaete, Neanthes virens. The purified enzyme was homogeneous by SDS-PAGE, with a molecular mass of 71 kDa by SDS-PAGE and 69 kDa by gel filtration, indicating that it is monomeric. The isoelectric point was 4.5 and optimum pH for the activity was 8.0. It showed a specific activity of 466.8 U/mg, which is the highest of known DCPs. The enzyme hydrolyzed angiotensin I to angiotensin II and sequentially released Phe-Arg and Ser-Pro from the C-terminus bradykinin, but does not cleave imido-bonds. Activity was completely inhibited by 1 mM EDTA and 5 mM o-phenanthroline, but it was not affected by serine and aspartic protease inhibitors. The original activity of EDTA-inactivated DCP was restored by addition of cobalt, manganese or low concentrations of zinc. The Km and Vmax values of the enzyme for Bz-Gly-His-Leu were 0.56 mM and 600 mumol/min per mg, respectively. The Ki values for specific mammalian ACE inhibitors, such as captopril and lisinopril, were 1.38 and 2.07 nM, respectively. In conclusion, we have shown the existence of a DCP from the polychaete, N. virens, with similar properties to those of mammalian ACE.