Soluble plasma peptidases

Vascular endothelial tissue peptidases and soluble plasma peptidases further contribute to peptide hydrolysis. As a consequence, the plasma half-life of most peptides is limited to minutes, as shown for endogenous peptides, such as angiotensin 11 and glucagon-like peptide 1 (Deacon et al., 1995 Werle Bemkop-Schniirch, 2006). In order to exert anti-hypertensive effect the ACE-inhibitory peptides need to resist different peptidases, such as ACE. In this regard ACE-inhibitory peptides can be classified into three groups the inhibitor type, of which the IC50 value is not affected by pre-incubation with ACE the substrate type, peptides that are hydrolysed by ACE to yield peptides with a weaker activity the pro-drug type inhibitor, peptides that are converted to true inhibitors by ACE or other proteases/peptidases. Only peptides... 

Hosono O, HommaT, Kobayashi H et al (1999) Decreased dipeptidyl peptidase IV enzyme activity of plasma soluble CD26 and its inverse correlation with HIV-1 RNA in HIV-1 infected individuals. Qin Immunol 91 283-295... 

The source of the peptidase will depend on the aim of the assay i.e., one may wish to measure catalytic activity in tissue or plasma samples, in which case specificity of the substrate is of prime importance. Conversely, if the assay is to be used in the development of peptidase inhibitors, the enzyme should be present in as pure a form as possible. We routinely express a recombinant form of ECE-1 in Chinese hamster ovary cells, and generally use the wild-type, membrane-bound form of the enzyme in crude membrane preparations. However, we have also designed a soluble, secreted form of ECE-1 containing a hexahistidine tag this allows purification on a nickel affinity resin and eliminates potential problems involved with the use of crude, particulate membranes. 

The distinction between penicillin-sensitive enzymes (PSEs) and PBPs appears arbitrary and is probably a reflection of the interests of the investigators. Three non-membrane bound water-soluble D-alanyl-D-alanine peptidases have been studied in detail (Frere and Joris, 1985) R39, R61 and alhus G enzymes. The R61 and alhus G enzymes have been crystallised and the crystal structure for R61 solved to 2.8 A resolution (Kelly et al., 1985). Although for both R61 and R39 it is very unlikely that these exocellular enzymes are the killing targets of (3-lactam antibiotics (Dusart et al., 1973), their study has provided useful models for the mechanism of inhibition of the enzymes anchored in the bacterial plasma membrane. The albus G enzyme contains zinc(II) and catalyses the hydrolysis of the C-terminal D-alanine of o-alanyl-o-alanine terminated peptides but it is only very weakly inactivated by penicillins and cephalosporins (Frere and Joris, 1985). 

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