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PubMed2004

Peptidase activities in rats treated chronically with N(omega)-nitro-L-arginine methyl ester (L-NAME).

The chronic treatment of rats with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) biosynthesis, results in hypertension. This inhibition of NO production results in activation of the renin-angiotensin system, with increased activity of the carboxypeptidase angiotensin I-converting enzyme (ACE). Since chronic NO inhibition increases ACE activity, we hypothesized that this inhibition could also affect the activities of other peptidases involved in cardiovascular functions. To test this possibility, we examined the activities of aminopeptidase M (APM), dipeptidyl peptidase IV (DPP IV), metalloendopeptidase 24.15 (MEP 24.15) and neutral endopeptidase 24.11 (NEP 24.11) in rat brain, heart, kidney, liver, lung and thoracic aorta. Male Wistar rats were treated chronically with L-NAME (80mgkg(-1) per day) administered in the drinking water for 4 weeks and their organs then removed and processed for the determination of peptidase activities. Treatment with L-NAME did not significantly alter the activities of the four peptidases in brain, heart, kidney, liver and lung. In contrast, in aorta, the activity of APM was slightly but significantly reduced whereas those of DPP IV and MEP 24.15 were markedly enhanced; NEP 24.11 was not detected in this tissue. Immunoblotting for DPP IV and MEP 24.15 showed increased expression in aortic tissue. Neither L-NAME (1-100microM) nor the NO donors sodium nitroprusside and 3-morpholinosydnonimine (SIN-1; 1-100microM) had any consistent effect on the activity of recombinant MEP 24.15 or renal DPP IV. The importance of MEP 24.15 in peptide metabolism was confirmed in pentobartibal-anesthetized rats pretreated with the MEP 24.15 inhibitor N-[1-(R,S)-carboxy-3-phenylpropyl]-Ala-Aib-Tyr-p-aminobenzoate (JA2), which significantly potentiated the hypotensive response to bradykinin. The altered peptidase activities seen in aorta may contribute to modulating vascular responses in this model of hypertension.

Animals↗
PubMed2005

Inhibition of dipeptidyl-peptidase IV catalyzed peptide truncation by Vildagliptin ((2S)-{[(3-hydroxyadamantan-1-yl)amino]acetyl}-pyrrolidine-2-carbonitrile).

Vildagliptin (NVP-LAF237/(2S)-{[(3-hydroxyadamantan-1-yl)amino]acetyl}-pyrrolidine-2-carbonitrile) was described as a potent, selective and orally bio-available dipeptidyl-peptidase IV (DPP IV, EC 3.4.14.5) inhibitor [Villhauer EB, Brinkman JA, Naderi GB, Burkey BF, Dunning BE, Prasad K, et al.1-[[(3-Hydroxy-1-adamantyl)amino]acetyl]-2-cyano-(S)-pyrrolidine: a potent, selective, and orally bioavailable dipeptidyl peptidase IV inhibitor with antihyperglycemic properties. J Med Chem 2003;46:2774-89]. Phase III clinical trials for the use of this compound in the treatment of Type 2 diabetes were started in the first quarter of 2004. In this paper, we report on (1) the kinetics of binding, (2) the type of inhibition, (3) the selectivity with respect to other peptidases, and (4) the inhibitory potency on the DPP IV catalyzed degradation of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and substance P. Vildagliptin behaved as a slow-binding DPP IV inhibitor with an association rate constant of 1.4x10(5)M(-1)s(-1) and a K(i) of 17nM. It is a micromolar inhibitor for dipeptidyl-peptidase 8 and does not significantly inhibit dipeptidyl-peptidase II (EC 3.4.11.2), prolyl oligopeptidase (EC 3.4.21.26), aminopeptidase P (EC 3.4.11.9) or aminopeptidase M (EC 3.4.11.2). There was no evidence for substrate specific inhibition of DPP IV by Vildagliptin or for important allosteric factors affecting the inhibition constant in presence of GIP and GLP-1.

Adamantane↗
PubMed2007

Neuropeptide Y (NPY) cleaving enzymes: structural and functional homologues of dipeptidyl peptidase 4.

N-terminal truncation of NPY has important physiological consequences, because the truncated peptides lose their capability to activate the Y1-receptor. The sources of N-terminally truncated NPY and related peptides are unknown and several proline specific peptidases may be involved. First, we therefore provide an overview on the peptidases, belonging to structural and functional homologues of dipeptidyl peptidase 4 (DP4) as well as aminopeptidase P (APP) and thus, represent potential candidates of NPY cleavage in vivo. Second, applying selective inhibitors against DP4, DP8/9 and DP2, respectively, the enzymatic distribution was analyzed in brain extracts from wild type and DP4 deficient F344 rat substrains and human plasma samples in activity studies as well as by matrix assisted laser desorption/ionisation-time of flight (MALDI-TOF)-mass spectrometry. Third, co-transfection of Cos-1 cells with Dpp4 and Npy followed by confocal lasermicroscopy illustrated that hNPY-dsRed1-N1 was transported in large dense core vesicles towards the membrane while rDP4-GFP-C1 was transported primarily in different vesicles thereby providing no clear evidence for co-localization of NPY and DP4. Nevertheless, the review and experimental results of activity and mass spectrometry studies support the notion that at least five peptidases (DP4, DP8, DP9, XPNPEP1, XPNPEP2) are potentially involved in NPY cleavage while the serine protease DP4 (CD26) could be the principal peptidase involved in the N-terminal truncation of NPY. However, DP8 and DP9 are also capable of cleaving NPY, whereas no cleavage could be demonstrated for DP2.

Animals↗
PubMed2003

Degradation of endomorphin-2 at the supraspinal level in mice is initiated by dipeptidyl peptidase IV: an in vitro and in vivo study.

Endomorphin-2 (Tyr-Pro-Phe-PheNH(2)) was discovered as an endogenous ligand for the mu-opioid receptor. The physiological function of endomorphin-2 as a neurotransmitter or neuromodulator may cease through the rapid enzymatic process in the synapse of brain, as for other neuropeptides. The present study was conducted to examine the metabolism of endomorphin-2 by synaptic membranes prepared from mouse brain. Major metabolites were free tyrosine, free phenylalanine, Tyr-Pro and PheNH(2). Both the degradation of endomorphin-2 and the accumulation of major metabolites were inhibited by specific inhibitors of dipeptidyl peptidase IV, such as diprotin A and B. On the other hand, the accumulation of Phe-PheNH(2) and Pro-Phe-PheNH(2) was increased in the presence of bestatin, an aminopeptidase inhibitor, whereas that of free phenylalanine and PheNH(2) was decreased. Furthermore, purified dipeptidyl peptidase IV hydrolyzed endomorphin-2 at the cleavage site, Pro(2)-Phe(3) bond. Thus, degradation of endomorphin-2 by brain synaptic membranes seems to take place mainly through the cleavage of Pro(2)-Phe(3) bond by dipeptidyl peptidase IV, followed by release of free phenylalanine and PheNH(2) from the liberated fragment, Phe-PheNH(2) by aminopeptidase. We have also examined that the effect of diprotin A on the antinociception induced by intracerebroventricularly administered endomorphin-2 in the mouse paw withdrawal test. Diprotin A simultaneously injected with endomorphin-2 enhanced endomorphin-2-induced antinociception. These results indicate that dipeptidyl peptidase IV may be an important peptidase responsible for terminating endomorphin-2-induced antinociception at the supraspinal level in mice.

Aminopeptidases↗
PubMed2003

Pyroglutamyl-peptidase I: cloning, sequencing, and characterisation of the recombinant human enzyme.

Pyroglutamyl-peptidase I (EC 3.4.19.3) is well known from bacteria and archaea, but has not previously been cloned or sequenced from any vertebrate. We describe the cloning and sequencing of the human (AJ278828) and mouse (AJ278829) forms of pyroglutamyl-peptidase I. The deduced amino acid sequences each consist of 209 residues and show approximately 30% identity with bacterial forms of the enzyme. They show clear homology to the enzyme from prokaryotes and place the mammalian forms of the enzyme in peptidase family C15 of the MEROPS database. The catalytic residues Glu81, Cys144, and His166 in the enzyme from Bacillus amyloliquefaciens are all conserved in the human sequence. A simple cartoon model of the human protein was constructed on the basis of the published crystal structures of pyroglutamyl-peptidase I forms from Thermococcus litoralis and B. amyloliquefaciens. The human enzyme was expressed by use of a baculovirus vector in Spodoptera frugiperda cells. The recombinant protein was enzymatically active and had properties similar to those described for the naturally occurring mammalian enzyme. Gel-filtration chromatography of the active enzyme gave a molecular mass of about 24kDa, showing that the enzyme is active as the monomer. This contrasted with indications that the prokaryotic enzymes may be tetrameric. Recombinant human pyroglutamyl-peptidase I was active on pGlu-aminomethylcoumarin in the range pH 6-9, with maximal activity being seen at pH 7.0-8.5; it showed an absolute requirement for a thiol-reducing agent. In crude preparations, the enzyme was completely stable for 90 min at 50 degrees C. The enzyme was inhibited by transition metal ions including Ni(2+), Zn(2+), and Cu(2+), and by sulfhydryl-blocking agents. Reversible inhibition was seen with 2-pyrrolidone (K(i)=50 microM), and surprisingly, with N-ethylmaleimide (K(i)=30 microM).

Amino Acid Sequence↗
PubMed1995

Human dipeptidyl peptidase IV gene promoter: tissue-specific regulation from a TATA-less GC-rich sequence characteristic of a housekeeping gene promoter.

The dipeptidyl peptidase IV gene encodes a plasma-membrane exopeptidase that is highly expressed in small intestine, lung and kidney. In order to better understand the mechanisms responsible for this tissue-specific expression we cloned, sequenced and functionally characterized the 5'-flanking region of the human dipeptidyl peptidase IV gene. The first 500 bases of the 5'-flanking sequence constituted an unmethylated CpG island, contained several Sp1-binding sites and lacked a consensus TATA box, all characteristics of gene promoters lacking tissue-specific expression. RNase-protection analysis using both small intestinal and Caco2 cell RNA indicated that the dipeptidyl peptidase IV transcript was initiated from no fewer than six major and 12 minor start sites. The 5'-flanking sequence also exhibited functional promoter activity in transient transfection experiments. Here, various lengths of the sequence were cloned upstream of a luciferase gene and introduced into cultured cells using lipofectin. A region located between bases -150 and -109 relative to the start of translation was found to be important for high-level promoter activity in both Caco2 and HepG2 cells. Moreover, Caco2 cells and HepG2 cells, which express high levels of dipeptidyl peptidase IV activity, exhibited much higher normalized luciferase activity after transfection than did 3T3, Jurkat or COS-7 cells, which have low enzyme levels. Sodium butyrate was found to increase both enzyme activity and normalized luciferase in HepG2 cells. Thus the dipeptidyl peptidase IV promoter possesses the ability to initiate transcription in a tissue-specific fashion in spite of having the sequence characteristics of a housekeeping gene promoter.

3T3 Cells↗
PubMed1995

Immunoadsorption of hepatic vesicles carrying newly synthesized dipeptidyl peptidase IV and polymeric IgA receptor.

Hepatocytes must transport newly synthesized apical membrane proteins from the basolateral to the apical plasma membrane. Our earlier morphological study showed that the apical proteins share a late (subapical) part of the transcytotic pathway with the well characterized polymeric immunoglobulin A receptor (Barr, V. A., and Hubbard, A. L. (1993) Gastroenterology 105, 554-571). Starting with crude microsomes from the livers of [35S]methionine-labeled rats, we sequentially immunoadsorbed first vesicles containing the endocytic asialoglycoprotein receptor and then (from the depleted supernatant) vesicles containing the polymeric IgA receptor. Biochemical characterization indicated that early basolateral and late endosomes were present in the first population but not in the second. Neither Golgi-, apical plasma membrane (PM)-, nor basolateral PM-derived vesicles were significant contaminants of either population. Both vesicle populations contained 35S-labeled receptor and 35S-labeled-dipeptidyl peptidase IV. Importantly, the elevated relative specific activity of the dipeptidyl peptidase (% of 35S-labeled/% immunoblotted) in the second population indicated that these vesicles must transport newly synthesized dipeptidyl peptidase IV. A distinct kind of vesicle was immunoadsorbed from a "carrier-vesicle fraction"; surprisingly, these vesicles contained little 35S-receptor and virtually no dipeptidyl peptidase IV. These results, together with previous kinetic data from in vivo experiments, are consistent with a computer-generated model predicting that newly synthesized dipeptidyl peptidase IV is delivered to basolateral endosomes, which also contain newly synthesized polymeric immunoglobulin A receptor. The two proteins are then transcytosed together to the subapical region.

Animals↗
PubMed1992

Ontogeny of prolyl endopeptidase, pyroglutamyl peptidase I, TRH, and its metabolites in rat pancreas.

We demonstrate that two enzymes, soluble unspecific pyroglutamyl peptidase I and prolyl endopeptidase, able to degrade thyrotropin-releasing hormone (TRH) in vitro were present in pancreas at the early stage of rat development. Specific particulate pyroglutamyl peptidase II remained undetectable during ontogenesis. Pyroglutamyl peptidase I specific activity increased until day 3 and decreased after day 5. Furthermore, prolyl endopeptidase specific activity rose slightly to a peak on postnatal day 20. A good correlation between immunoreactive TRH and deaminated TRH (TRH-OH) was found in the 1st wk after birth. However, His-Pro diketopiperazine (DKP) levels were stable and low during development. We show that hot acidic extraction conditions could artefactually generate His-Pro DKP. In vivo, active site-directed inhibitors of pyroglutamyl peptidase I and prolyl endopeptidase enzymes do not show any TRH-deamidating and/or pyroglutamyl peptidase I pathways in neonatal rat pancreas. The data suggest that these two enzymes are not involved in intra- or extracellular control of TRH levels in neonatal rat pancreas and that pancreatic TRH content appears to be principally regulated by biosynthetic steps. Nevertheless, low levels of endogenous His-Pro DKP and TRH-OH identified in neonatal rat pancreas suggest that TRH or TRH-like peptides may be metabolized in this tissue in intact rats, albeit at low rates.

Aging↗
PubMed1989

Sodium butyrate induces pyroglutamyl peptidase I and decreases thyrotropin-releasing hormone receptors in GH3 cells.

The effect of sodium butyrate treatment on TRH-degrading enzymes and TRH receptors in GH3 cells was investigated. The specific activity of pyroglutamyl peptidase I (EC 3.4.19.3) was increased by exposure to sodium butyrate in a time- and concentration-dependent manner, whereas the specific activity of prolyl endopeptidase (EC 3.4.21.26) was unchanged. The maximal effect occurred at a concentration of 1 mM sodium butyrate and 16 h after exposure. The increase was reversible upon removal of sodium butyrate from the cell culture. Cycloheximide totally blocked the stimulation, indicating that the increase was due to new protein synthesis. Sodium butyrate had no effect on pyroglutamyl peptidase I activity in the AtT-20 cell line. [methyl-3H]TRH binding to intact GH3 cells was reduced to 70% of the control value when cells were exposed to 1 mM sodium butyrate for 8 h. A maximal decrease in binding to 40% of the control value occurred after 16 h of exposure. The Kd of [methyl-3H]TRH binding was not changed. Sodium butyrate altered GH3 cell morphology, but the morphological changes occurred after alterations of pyroglutamyl peptidase I activity and [methyl-3H]TRH-binding sites. Other agents known to alter GH3 cell morphology had no effect on pyroglutamyl peptidase I activity. These results indicate that sodium butyrate can in some respects mimic the action of T3 on GH3 cells. Moreover, they provide further evidence that the activity of pyroglutamyl peptidase I, but not prolyl endopeptidase, is subject to regulation in the GH3 cell.

Aminopeptidases↗
PubMed1998

Soluble and membrane-bound pyroglutamyl-peptidase I activity in the developing cerebellum and brain cortex.

Developmental changes of soluble and particulate pyroglutamyl (pGlu)-peptidase I activities in the rat brain cortex and in the cerebellum are described in this work. The enzyme activity has been measured spectrofluorimetrically using pGlu-b-naphthylamide as substrate (in the presence and absence of EDTA and DTT, necessary activators of the enzyme) in both soluble and particulate fractions. In the soluble fraction of the cerebellum and brain cortex, pGlu-peptidase I activity is high in the perinatal period and decreases two or three folds subsequently, at a later stage in the cerebellum than in the brain cortex, reaching adult levels at the end of the first postnatal month. The decrease in the activity of pGlu-peptidase observed in this work coincides with increasing levels of brain thyroliberin concentration after the second postnatal week. The particulate pGlu-peptidase I activity, obtained after osmotic shock and high-salt treatment, shows less significant changes during brain development in the areas under study. It is suggested that cytosolic pGlu-peptidase I could play a part in the normal development of the rat central nervous system.

Animals↗
PubMed1985

Histochemical demonstration of peptidases in the human kidney.

The localization of several peptidases in the human kidney was investigated histochemically. The membrane-bound peptidases, aminopeptidase A (APA), aminopeptidase M, gamma-glutamyltransferase (gamma-GT) and dipeptidylpeptidase IV, were mainly demonstrable in the brush border of the proximal tubule. In addition, APA was found in the glomeruli, while gamma-GT was found in the basal labyrinth of the proximal tubule. The lysosomal peptidases, dipeptidylpeptidase I and cathepsin B, were most strongly concentrated in the different-sized lysosomes of the proximal tubule, but they were also found in the small lysosomes of the distal tubule. Dipeptidylpeptidase II showed only a weak reaction in lysosomes of the proximal tubule. It is concluded that, in comparison with other previously studied species, the human kidney has a well-developed equipment with membrane-bound and lysosomal peptidases.

Adult↗
PubMed1989

Kinetic and end-point microdensitometry (section biochemistry) of gamma-glutamyl transpeptidase and dipeptidyl peptidase IV in the mature mouse decidua and visceral yolk sac.

gamma-Glutamyl transpeptidase (EC 2.3.2.2) and dipeptidyl peptidase IV (EC 3.4.14.5) were measured in mature mouse decidual and visceral yolk sac epithelial cells by means of kinetic (continuous) and end-point (static) microdensitometry (section biochemistry). For continuous measurements a new device for starting the enzyme reaction allowed the first readings to be made already during its very early phase. Since the initial reaction rates of both peptidases were very different in the plasma membrane of decidual and also in the visceral yolk sac epithelial cells, it was difficult to select a sufficient number of cells of the same activity for representative measurements on the basis of kinetic microdensitometry. Static section biochemistry was performed also for statistical reasons, i.e., in order to obtain information about the distribution of the activities of the decidual and visceral epithelial cells and the number of measurements required to guarantee valid data. Various groups of decidual and visceral yolk sac epithelial cells with different gamma-glutamyl transpeptidase and dipeptidyl peptidase IV activities were formed. In this way, different activities of gamma-glutamyl transpeptidase were measured in the plasma membrane of the cells of the antimesometrial, intermediate, and mesometrial decidua. Compared with dipeptidyl peptidase IV, gamma-glutamyl transpeptidase was significantly more active in the plasma membrane of the antimesometrial decidual cells and microvillous zone of the visceral yolk sac epithelial cells.

Animals↗
PubMed1986

Complementary action of dipeptidyl peptidase IV and aminopeptidase M in the digestion of beta-casein.

Purified bovine beta-casein was digested in vitro with varying mixtures of purified proteinases and peptidases including trypsin, chymotrypsin, dipeptidyl peptidase IV (DP IV), aminopeptidase M and prolidase. In digestion mixtures without DP IV the yield of free amino acids was considerably lower than in the corresponding assays with this peptidase. Especially, the release of proline increases drastically from almost zero to the theoretical amount in the presence of DP IV. Quantitative results indicated that the specificities of the two microvillar peptidases (aminopeptidase M and DP IV) optimally complemented each other. This effect elucidates the hitherto obscure physiological role of intestinal DP IV. A similar effect may also apply to other caseins and nutritional proteins.

Amino Acid Sequence↗
PubMed1984

Dipeptidyl peptidase IV of human lymphocytes. Evidence for specific hydrolysis of glycylproline p-nitroanilide in T-lymphocytes.

Glycylproline p-nitroanilide is hydrolysed in lymphocytes from human blood exclusively by dipeptidyl peptidase IV. This was demonstrated by specific inhibition with N-alanylprolyl-O-(4-nitrobenzoyl)hydroxylamine and di-isopropyl phosphorofluoridate and by studying the membrane localization of dipeptidyl peptidase IV and determining specific dipeptidyl peptidase II activity. Additional evidence that dipeptidyl peptidase IV is a marker for T-lymphocytes, obtained from determinations of biochemical activity on intact lymphocyte preparations and correlation studies with other T-cell markers, is also presented.

Dipeptides↗
PubMed1994

Localization of aminopeptidase N and dipeptidyl peptidase IV in pig striatum and in neuronal and glial cell cultures.

The subcellular distribution of the plasma membrane ectoenzymes, aminopeptidase N (aminopeptidase M) and dipeptidyl peptidase IV, has been examined by fractionating homogenates of porcine striata by a discontinuous Percoll gradient centrifugation procedure which distinguishes fractions containing pre- and post-synaptic elements. The two enzymes showed different distributions--dipeptidyl peptidase IV did not show a significant pre-synaptic location, whereas aminopeptidase N was present on both pre- and post-synaptic fractions. Immunofluorescent staining on mixed and neuron-enriched primary cultures of pig striatal tissue using affinity purified antibodies to the aminopeptidase and to the dipeptidyl peptidase revealed the ectoenzymes on distinct populations of cells. The astrocytic identity of the aminopeptidase N-staining cells was established by correlation with immunostaining for glial fibrillary acidic protein and for vimentin by confocal microscopy. Ultracryosections of striatum immunostained with gold-labelled immunoglobulins of differing diameters demonstrated aminopeptidase N on pericytes and confirmed its location on endothelial and astrocytic glial cells. Thus, several independent approaches indicated that aminopeptidase N, in addition to being present on endothelial and synaptic membranes, is found on astrocytes and pericytes in the perivascular neuropil, whereas dipeptidyl peptidase IV is less widely distributed on microvessels and appears not to have a synaptosomal location.

Aminopeptidases↗
PubMed1991

Extended investigation of the substrate specificity of dipeptidyl peptidase IV from pig kidney.

The substrate specificity of dipeptidyl peptidase IV (dipeptidyl peptide hydrolase, EC 3.4.14.5) from pig kidney was investigated, using a series of substrates, in which the amino-acid residue in position P1, a structural derivative of proline, was altered with respect to ring size and substituents. It was demonstrated that dipeptidyl peptidase IV hydrolyses substrates of the type Ala-X-pNA, where X is proline (Pro), (R)-thiazolidine-4-carboxylic acid (Thz), (S)-pipecolic acid (Pip), (S)-oxazolidine-4-carboxylic acid (Oxa), or (S)-azetidine-2-carboxylic acid (Aze). The ring size and ring structure of the residue in the P1 position influence the rate of enzyme-catalysed hydrolysis of the substrate. The highest kcat value (814 s-1) was found for Ala-Aze-pNA. In contrast, the kcat value for Ala-Pro-pNA is nearly 55 s-1. With all substrates of this series, the rate-limiting step of the hydrolysis by dipeptidyl peptidase IV is the deacylation reaction. Compounds of substrate-like structure, in which the P2 residue has an R-configuration, are not hydrolysed by dipeptidyl peptidase IV.

Animals↗
PubMed1991

[Distribution of the activity of some peptidases in the pancreas of human embryo].

In the developing pancreas of human embryos and fetusses (in weeks 4 to 20 of the intrauterine life) activities of aminopeptidase A (APA) and M (APM), dipeptidyl peptidase IV (DPP IV), and gamma-glutamyl transferase (GGT) were studied in cryostat sections using methods as recommended by Lojda (J. Histochem. Cytochem. 29, 481 (1981)). In the youngest embryos (4-7 weeks) a high DPP IV activity was recorded in the epithelium of differentiating primitive glandular tubules. Activity of other peptidase was low. In older fetusses (8-20 weeks, particularly after week 15) activities of all peptidases studied gradually increase. In acinic "anlage" a high DPP IV activity was observed. APM activity was substantially lower. The reaction product originating in the reaction for GGT is localized particularly at the luminal surfase of epithelial lining of primitive tubuli. In this period APA activity was hardly discernible. This is in contrast with other organs. High DPP IV and APM activities were present in cells of differentiating Langerhans islets. The appearance of peptidases studied does not occur simultaneously, however, their activities increase with the morphological differentiation.

Aminopeptidases↗
PubMed1986

Processing of pro-colipase and trypsinogen by pancreatic dipeptidyl peptidase IV.

Purified dipeptidyl peptidase IV from porcine pancreas or from human placenta cleaves N-terminal dipeptides from two proteins of the pancreatic juice, namely trypsinogen and pro-colipase. Phenylalanyl-proline is very effectively released (Km approximately 50 microM) from bovine or porcine trypsinogen. Both purified dipeptidyl peptidases also rapidly cleave valyl-proline from the N-terminus of porcine pro-colipase. This degradation does not increase the colipase activity of the precursor. However, under certain conditions, which are not fully understandable at present, dipeptidyl peptidase IV releases more slowly a second dipeptide, aspartyl-proline, from pro-colipase, and this results in a partial activation. Dipeptidyl peptidase IV apparently lines the excretory ducts of porcine pancreas and, therefore, is in close contact to the proteins of pancreatic juice in vivo. The possible significance of these degradations is discussed.

Amino Acids↗