Post-proline cleaving enzyme (prolyl endopeptidase) from bovine brain

A post-proline cleaving enzyme [prolyl endopeptidase, EC 3.4.21.26] was purified about 3,700-fold from an extract of bovine brain by a series of column chromatographies on DEAE-Sephadex, hydroxyapatite and PCMB-T-Sepharose, and gel filtration on Sephadex G-200 using N-carbobenzoxy-Gly-Pro-beta-naphthylamide (Z-Gly-Pro-2-NNap), thyrotropin releasing hormone (TRH) and oxytocin as substrates. The purified enzyme appeared homogeneous as judged by disc gel and SDS gel electrophoreses. The enzyme was most active at pH 7.5 and 7.2 with Z-Gly-Pro-2-NNap and TRH, respectively, and hydrolyzed peptide bonds involving Pro-X (X=amino acid, peptide, ester and amide) bonds of synthetic substrates, oxytocin, vasopressin, neurotensin, substance P, tuftsin, bradykinin, and insulin B chain. However, the enzyme was inert toward collagen, gelatin, and casein. The enzyme was completely inactivated by diisopropylphosphorofluoridate (DFP), Z-Gly-Pro-chloromethyl ketone and p-chloromercuribenzoate (PCMB), while it was not inhibited by phenylmethane sulfonylfluoride (PMSF) or metal chelators. Determination of the amino acid composition revealed that the enzyme contained 25 half-cystines. Modification of three cysteine residues of the enzyme by PCMB led to complete inactivation. The isoelectric point of the enzyme was 4.8, and the molecular weight was estimated to be 76,000 by ultracentrifugal analysis and 75,000-74,000 by both gel filtration and sodium dodecyl sulfate (SDS) gel electrophoresis, suggesting that the enzyme is present as a monomer. These results indicate that the post-proline cleaving enzyme from bovine brain is very similar to those previously purified from lamb brain and kidney in its enzymatic properties, substrate specificity and physicochemical properties, in sharp contrast with the results obtained by Tate, who reported that the bovine brain prolyl endopeptidase was inert toward oxytocin, vasopressin and bradykinin.     

Post-proline cleaving enzyme. Purification of this endopeptidase by affinity chromatography.

The endopeptidase, post-proline cleaving enzyme, has been purified 10,500-fold in an overall yield of 18% from lamb kidney. The enzyme possesses a specific activity of 45 mumol/mg/min as tested with the substrate Z-Gly-Pro-Leu-Gly (Km = 6.0 X 10(-5)), has a molecular weight of 115,000, is comprised of two subunits with a molecular weight of 57,000, and exhibits maximal activity at pH 7.5 to 8.0. With the exception of the -Pro-Pro linkage, the -Pro-X-peptide bond (X equals L- and D-amino acid residues) located internally in the peptide sequence can be hydrolyzed (cleavage occurs faster when X = lipophilic side chain as compared to X = acidic side chain). The appropriate -Pro-X- bonds in zinc-free porcine insulin, oxytocin, arginine vasopressin, angiotensin II, bradykinin-potentiating factor were cleaved. Human gastrin, adrenocorticotropic hormone, denatured guinea pig skin collagen, and ascaris cuticle collagen were not degraded. Dipeptides with the structure Z-Pro-LD-X competitively inhibit post-proline cleaving enzyme.     

Molecular heterogeneity of angiotensin converting enzyme in human cerebrospinal fluid.

Three different molecular forms of angiotensin converting enzyme (ACE) (approximately Mr 150,000, 80,000 and 40,000, respectively), have been recovered from human cerebrospinal fluid. All three enzymes were inhibited by captopril and enalapril and their activity was potentiated by chloride ions. They were capable of degrading Leu-enkephalin-Arg6 and substance -P, but gave no conversion of neurokinin A. In all these aspects, the CSF enzymes were identical with the human pulmonary enzyme. The Mr 40,000 form of ACE is the smallest active form of the enzyme hitherto reported and is likely to represent a fragment of the C-terminal part of native ACE, where its active center is located.     

Characterization of a substance P-Gly12 amidating enzyme in human cerebrospinal fluid

Enzyme activity capable of converting the glycine-extended substance P precursor, substance P-Gly12, into substance P was purified from human cerebrospinal fluid. The conversion reaction was monitored by radioimmunoassay measurement of substance P formation. The chemical identity of the product was verified by reversed-phase HPLC. The enzyme reaction was stimulated by Cu(II) ion and ascorbic acid and inhibited by the presence of diethyldithiocarbamate. By HPLC molecular sieving, the major enzyme activity appeared as a protein of 26,000 molecular weight.     

Characterization of the human ventricular cerebrospinal fluid proteome obtained from hydrocephalic patients

The continuing expansion of proteomic technology has been fueled by the potential for discovering novel biomarkers that may be used for the early detection of disease. It has been proposed that human cerebrospinal fluid (CSF), which surrounds and protects the brain and spinal cord from traumatic injury, may be a valuable target for the diagnosis of a variety of conditions such as Alzheimer's disease, traumatic brain injury, amyotrophic lateral sclerosis and Parkinson's disease. The immense complexity of biofluids, however, still requires that considerable development be made in the analytical techniques used so that comprehensive coverage of the proteins present in such samples is achieved. Using a simple separation strategy the protein complement of human ventricular cerebrospinal fluid obtained from patients with hydrocephalus was evaluated. The study resulted in the identification of over 1500 unique proteins that were found within all nine CSF samples that were analyzed. Comparison with the HUPO serum proteome database demonstrated that human ventricular CSF contains a large array of proteins that may be unique to CSF. This analysis greatly increases our knowledge of the protein content of this clinically important biofluid.     

Neuropeptides in human cerebrospinal fluid

Ten neuropeptides were measured by RIA in human cerebrospinal fluid obtained from 30 normal volunteers. The levels of seven peptides (corticotropin releasing factor, adrenocorticotropin, vasoactive intestinal peptide, somatostatin, beta-endorphin, beta-lipotropin, and the N-terminal fragment of proopiomelanocortin) were highly, positively correlated with one another. This result is consistent with the hypothesis that cerebrospinal fluid levels of these seven peptides are a function of some common regulatory factor, such as shared release into the cerebrospinal fluid.     

Endorphins in human cerebrospinal fluid

Opiate activity in CSF samples drawn from patients with suspected intracranial hydrodynamic dysfunction has been fractionated on Sephadex G-10 and separated by column electrophoresis in agarose suspension. From the Sephadex G-10 chromatography two receptor active fractions (FI and FII) were recovered. Both FI and FII were further resolved by the electrophoresis. FI separated into at least four components and FII into two components. The study also includes a comparison of the endorphin concentrations in CSF (samples drawn from healthy volunteers) measured by receptorassay with those detected by radioimmunoassay of beta-endorphin, [Met]enkephalin and dynorphin, respectively. The data obtained indicated negligible quantities of the radioimmunoassayable endorphins in the total CSF opiate activity.     

Post-proline cleaving enzyme. Synthesis of a new fluorogenic substrate and distribution of the endopeptidase in rat tissues and body fluids of man.

Synthesis and application of the first fluorogenic substrate, N-carbobenzoxyglycylprolyl-4-methylcoumarinyl amide (Z-Gly-Pro-MeCouNH) for the determination of the post-proline cleaving enzyme (EC 3.4.21.-) were reported. Maximal activity of the enzyme purified from lamb kidney for the new substrate was observed at pH 7.0. This substrate showed a higher affinity (Km = 0.02 mM) for the enzyme than the proline containing substrates studied previously and allowed the detection of 10-50 ng post-proline cleaving enzyme activity per ml sample after a 1 min incubation period. Distribution of post-proline cleaving enzyme and other proline specific peptidases in rat tissues was studied using Z-Gly-Pro-MeCouNH and other proline-containing substrates. High post-proline cleaving enzyme activity was observed in testis, liver and skeletal muscle. Inhibition experiments indicated that post-proline cleaving enzyme activity was completely inactivated by 0.1 mM diisopropylphosphofluoridate and Z-Gly-Pro-chloromethylketone, as had been found in the case of the enzyme isolated from lamb kidney. Activity in human body fluids was also tested for levels of post-proline cleaving enzyme activity using Z-Gly-Pro-MeCouNH and semen was found to show the highest cleaving activity.     

A bromine compound isolated from human cerebrospinal fluid

A new bromine compound with properties characteristic of a ketone was isolated from human cerebrospinal fluid. It was degraded by alkali treatment producting acetic acid, glycoli acid, oxalic acid, HBr and 1-methylheptanol. By this treatment, a part of the compound was converted to di-1-methylheptyl-2,5-dioxocyclohexane-1,4-dicarboxylate. These degradation products were also obtained from synthetic 1-methylheptyl-γ-bromoacetoacetate by alkali treatment. 1-methylheptyl-γ-bromoacetoacetate and realted substances were synthesized and compared with the isolated bromine compound in chemical properties, infrared spectra, spectra of nuclear magnetic resonance, and elemental analysis, etc. These results showed that the isolated bromine compound corresponded well to 1-methylheptyl-γ-bromoacetoacetate (synonym of 2-octyl-γ-bromoacetoacetate).     

Studies of specificity and inhibition of human cerebrospinal fluid dynorphin converting enzyme.

Dynorphin-converting activity was recently discovered in human cerebrospinal fluid. This enzyme (hCSF-DCE) cleaves dynorphin A, dynorphin B and alpha-neoendorphin to release Leu-enkephalin-Arg6. To characterize the enzyme further we used several protease inhibitors, including N-peptidyl-O-acyl hydroxylamines which are known to act as potent irreversible inhibitors of serine and cysteine proteinases. No irreversible inactivation occurred but strong, reversible effects on the dynorphin-converting activity by some of the inhibitors tested could be observed. Although, hCSF-DCE binds its substrates (dynorphin A and B) in the microM-mM concentration range, it exhibits high specificity in recognizing and cleaving the linkage between the two basic amino acids in the substrate sequence.     

Zinc and copper in human cerebrospinal fluid

Zinc and copper have been estimated in CSF of 14 normal volunteers, nine men and five women. Zinc was analyzed by limited-aspiration flame atomic absorption spectrophotometry using a deuterium continuum light source. Copper was analyzed in 0.1% HNO₃ by flameless atomic absorption spectrophotometry with a graphite cuvette on a flameless atomizer. Recovery of added zinc varied less than 5% and that of the added copper varied less than 8%. CSF zinc was 31.5±19.8 μg/L (mean ± 1 SD); CSF copper, 7.5±3.1 μ/L. Values obtained for CSF zinc are about 1/2 those we and others obtained previously, the decrease related almost exclusively to removal of interference by the CSF matrix, which produced spuriously elevated values without use of the deuterium light source. Values obtained for CSF copper were approximately one-tenth those we and others had obtained previously. The decrease related, in part, to the removal of matrix effects, but also to improvement of the signal-to-noise ratio present in other techniques.     

Beta-endorphin-immunoreactive components in human cerebrospinal fluid

Cerebrospinal fluid (CSF) from patients without neurological disorder was analyzed after Sep-Pak extraction for beta-endorphin (beta-EP)-immunoreactive components by combined reversed-phase high-performance liquid chromatography (HPLC) and radioimmunoassay. A C-terminal directed antibody detected one major immunoreactive component, probably identical with beta-EP1-31. An N-terminal directed antibody detected several immunoreactive components. One co-eluted with beta-EP1-31 but the others are probably C-terminal truncated or otherwise modified forms of beta-EP1-31. However, they eluted differently from beta-EP1-16 (alpha-endorphin), beta-EP1-26, 1-27 and alpha,N-acetyl-beta-EP1-31. Alternatively, some of the fragments may represent C-terminal extended forms of pro-enkephalin A-derived Met-enkephalin. A Met-enkephalin antiserum detected several immunoreactive components probably representing N-terminal extended forms; neither of them were identical with the beta-EP-immunoreactive components. The results illustrate the heterogeneity of the beta-EP-immunoreactive components in CSF and the need to characterize the beta-EP radioimmunoassay before its application to biological extracts.     

Assay and biochemical characterization of angiotensin-I-converting enzyme in cerebrospinal fluid

A spectrofluorimetric method was adapted for determination of angiotensin-I-converting enzyme (ACE) in untreated native cerebrospinal fluid (CSF). Benzyloxycarbonyl-phenylalanyl-histidyl-leucine was applied as enzyme substrate. The biochemical behavior of ACE of CSF (CACE) was studied. The pH optimum was found to be 8.0 using borax phosphate buffer. The determination of Km was 10.7 +/- 3.3 (SD) mumol/l. ACE could be blocked by 8-hydroxyquinoline (100%) and phenanthroline (80%), but only slight inhibition was observed by teprotide (43%), EDTA (40%) and captopril (31%). The influence of various drugs on CACE was also tested. The different biochemical behavior of CACE compared to serum ACE suggested that an isoenzyme exists in CSF. CACE has been found to be elevated in neuroimmunological and inflammatory disorders of the nervous system compared to levels in healthy controls.     

The human cerebrospinal fluid metabolome

With continuing improvements in analytical technology and an increased interest in comprehensive metabolic profiling of biofluids and tissues, there is a growing need to develop comprehensive reference resources for certain clinically important biofluids, such as blood, urine and cerebrospinal fluid (CSF). As part of our effort to systematically characterize the human metabolome we have chosen to characterize CSF as the first biofluid to be intensively scrutinized. In doing so, we combined comprehensive NMR, gas chromatography-mass spectrometry (GC-MS) and liquid chromatography (LC) Fourier transform-mass spectrometry (FTMS) methods with computer-aided literature mining to identify and quantify essentially all of the metabolites that can be commonly detected (with today's technology) in the human CSF metabolome. Tables containing the compounds, concentrations, spectra, protocols and links to disease associations that we have found for the human CSF metabolome are freely available at http://www.csfmetabolome.ca.     

Distribution of post-proline cleaving enzyme in human brain and the peripheral tissues

Summary We have studied the distribution of post-propline cleaving enzyme activity in the various tissues in humans using 7-(succinyl-Gly-Pro)-4-methylcoumarinamide as substrate. The post-propline cleaving enzyme activity was high in muscle, testes, kidney and submandibular gland, but was low in the heart, mesenterium and aorta. In the brain, relatively high post-propline cleaving enzyme activity was observed in the cerebral cortex, but other brain regions showed a very low enzyme activity.On Sephadex G-100 column chromatography, enzyme activity in human kidney showed a major peak and a minor peak. The major peak coincided with the enzyme in human cerebral cortex, but was different from human serum enzyme. Diisopropylfluorophosphate, a serine protease inhibitor, strongly inhibited the enzyme activity of each active fraction. The enzyme in the cerebral cortex and kidney was inhibited by heavy metals and thiol blocking agents. However, inhibition of enzyme activity in the serum was not observed with such inhibitors. Therefore, we suppose that post-proline cleaving enzyme activity in the brain is similar, if not identical, to that in the kidney.     

Proteomic analysis of cerebrospinal fluid from multiple sclerosis patients

Multiple sclerosis is an autoimmune inflammatory demyelinating disease of the central nervous system. Disease mechanisms in multiple sclerosis at the molecular level remain poorly understood and no reliable proteinaceous disease markers are available yet. The goal of the present study is the construction of a protein database of two-dimensional gel electrophoresis (2-DE) separated cerebrospinal fluid (CSF) proteins from multiple sclerosis patients. By means of liquid chromatography tandem mass spectrometry 65 different proteins were identified from 300 spots. Eighteen of these proteins have not been reported previously on 2-DE gels of CSF. Here we report on the identification of these proteins and discuss their potential relation to multiple sclerosis.     

Neuropeptide Y immunoreactivity in human cerebrospinal fluid

Neuropeptide Y (NPY) immunoreactivity has been determined in human cerebrospinal fluid (CSF). High pressure liquid chromatography revealed that the NPY immunoreactivity co-eluted with authentic NPY. The range of NPY levels was 108 +/- 18 pg/ml (mean +/- S.D.) in a group of 28 normal subjects. In five additional subjects NPY immunoreactivity was measured in 4 sequential 8 ml aliquots of CSF to determine whether a rostro-caudal gradient was present. No significant differences in NPY levels were detected between any of the 4 aliquots.