Prolinase and non-specific dipeptidase of human kidney

State of the Art in the Development of Human Serum Carnosinase Inhibitors

Human serum carnosinase is an enzyme that operates the preferential hydrolysis of dipeptides with a C-terminus histidine. Only higher primates excrete such an enzyme in serum and cerebrospinal fluid. In humans, the serum hydrolytic rate has high interindividual variability owing to gene polymorphism, although age, gender, diet, and also diseases and surgical interventions can modify serum activity. Human genetic diseases with altered carnosinase activity have been identified and associated with neurological disorders and age-related cognitive decline. On the contrary, low peripheral carnosinase activity has been associated with kidney protection, especially in diabetic nephropathy. Therefore, serum carnosinase is a druggable target for the development of selective inhibitors. However, only one molecule (i.e., carnostatine) has been discovered with the purpose of developing serum carnosinase inhibitors. Bestatin is the only inhibitor reported other than carnostatine, although its activity is not selective towards serum carnosinase. Herein, we present a review of the most critical findings on human serum carnosinase, including enzyme expression, localization and substrate selectivity, along with factors affecting the hydrolytic activity, its implication in human diseases and the properties of known inhibitors of the enzyme.

Tutorial review for peptide assays: An ounce of pre-analytics is worth a pound of cure

The recent increase in peptidomimetic-based medications and the growing interest in peptide hormones has brought new attention to the quantification of peptides for diagnostic purposes. Indeed, the circulating concentrations of peptide hormones in the blood provide a snapshot of the state of the body and could eventually lead to detecting a particular health condition. Although extremely useful, the quantification of such molecules, preferably by liquid chromatography coupled to mass spectrometry, might be quite tricky. First, peptides are subjected to hydrolysis, oxidation, and other post-translational modifications, and, most importantly, they are substrates of specific and nonspecific proteases in biological matrixes. All these events might continue after sampling, changing the peptide hormone concentrations. Second, because they include positively and negatively charged groups and hydrophilic and hydrophobic residues, they interact with their environment; these interactions might lead to a local change in the measured concentrations. A phenomenon such as nonspecific adsorption to lab glassware or materials has often a tremendous effect on the concentration and needs to be controlled with particular care. Finally, the circulating levels of peptides might be low (pico- or femtomolar range), increasing the impact of the aforementioned effects and inducing the need for highly sensitive instruments and well-optimized methods. Thus, despite the extreme diversity of these peptides and their matrixes, there is a common challenge for all the assays: the need to keep concentrations unchanged from sampling to analysis. While significant efforts are often placed on optimizing the analysis, few studies consider in depth the impact of pre-analytical steps on the results. By working through practical examples, this solution-oriented tutorial review addresses typical pre-analytical challenges encountered during the development of a peptide assay from the standpoint of a clinical laboratory. We provide tips and tricks to avoid pitfalls as well as strategies to guide all new developments. Our ultimate goal is to increase pre-analytical awareness to ensure that newly developed peptide assays produce robust and accurate results.

Two broad-specificity dipeptide hydrolysing activities from cytoplasm of guinea pig brain, both of which contain prolinase but neither of which contain carnosinase activity

Two dipeptide hydrolysing activities were purified from cytoplasm of guinea pig brain. Dipeptide hydrolase I has been shown to be a strict dipeptidase requiring a free amino and a free carboxy terminus, while dipeptide hydrolase II displays very low activity against Leu-Leu-Leu. Of the 41 dipeptides presented to both enzymes, 25 were hydrolysed by both enzymes, while six (including carnosine) were hydrolysed by neither. Six were hydrolysed solely by dipeptide hydrolase I and four were hydrolysed solely by Pro-Leu hydrolase II. Kinetic analysis suggested that dipeptides which were hydrolysed with unfavourable kinetics or which were not hydrolysed by one dipeptide hydrolase were generally hydrolysed with more favourable kinetics by the other dipeptide hydrolase. Dipeptide hydrolase I displays optimum activity at pH 9.0, while dipeptide hydrolase II was optimally active at pH 8.0. Both enzymes were inhibited by 1,10-phenanthroline, p-chloromercuribenzoate and bestatin. Dipeptide hydrolase II was more strongly inhibited by arphamenine B than was dipeptide hydrolase I. Dipeptide hydrolase II was also inhibited by N-ethyl maleimide, while dipeptide hydrolase I was inhibited by dithiothreitol. Native M(r) values of 70,000 and 67,000 were computed for dipeptide hydrolase I and dipeptide hydrolase II, respectively. Sodium dodecyl sulphate polyacrylamide gel electrophoresis conducted with each enzyme under denaturing conditions suggested that both enzymes were comprised of a single polypeptide chain.

Proline specific peptidases

Proline is unique among the 20 amino acids due to its cyclic structure. This specific conformation imposes many restrictions on the structural aspects of peptides and proteins and confers particular biological properties upon a wide range of physiologically important biomolecules. In order to adequately deal with such peptides, nature has developed a group of enzymes that recognise this residue specifically. These peptidases cover practically all situations where a proline residue might occur in a potential substrate. In this paper we endeavour to discuss these enzymes, particularly those responsible for peptide or protein hydrolysis at proline sites. We have detailed their discovery, biochemical attributes and substrate specificities and have provided information as to the methodology used to detect and manipulate their activities. We have also described the roles, or potential roles that these enzymes may play physiologically and the consequences of their dysfunction in varied disease states.

High-performance liquid chromatographic enantioseparation of glycyl di- and tripeptides on native cyclodextrin bonded phases. Mechanistic considerations

Di- and tripeptides containing at least one glycine moiety were separated into enantiomers on alpha-, beta- and gamma-cyclodextrin bonded phases after their precolumn derivatization with 9-fluorenylmethyl chloroformate (FMOC-Cl). It is shown that the choice of a suitable cyclodextrin bonded phase used with a nonaqueous polar mobile phase offers a wide range of possibilities to optimize enantioselectivity. Use of the FMOC derivative greatly enhances sensitivity, stability and enantioselectivity. It is postulated that under reversed-phase conditions the inclusion complex formation between the hydrophobic aromatic part of the FMOC-functionalized peptides and non-polar cyclodextrin cavity interior is the major factor contributing to retention. However, under these conditions there seems to be insufficient interaction between the hydrophilic peptide chain and cyclodextrin hydroxyls. Hence no chiral recognition and enantiomeric separation is observed. In systems operating with polar organic mobile phases the inclusion complex is suppressed as the cyclodextrin cavity is largely occupied by the mobile phase. The enantioselectivity observed is caused by hydrogen bonding between peptide chain and the hydroxyl groups at the mouth of the cyclodextrin. The stereospecific interactions depend very strongly on the cyclodextrin size, the length of the peptide chain and the mobile phase composition.