Profiling Substrate Specificity of the SUMO Protease Ulp1 by the YESS–PSSC System to Advance the Conserved Mechanism for Substrate Cleavage

SUMO modification is a vital post-translational regulation process in eukaryotes, in which the SUMO protease is responsible for the maturation of the SUMO precursor and the deconjugation of the SUMO protein from modified proteins by accurately cleaving behind the C-terminal Gly–Gly motif. To promote the understanding of the high specificity of the SUMO protease against the SUMO protein as well as to clarify whether the conserved Gly–Gly motif is strictly required for the processing of the SUMO precursor, we systematically profiled the specificity of the S. cerevisiae SUMO protease (Ulp1) on Smt3 at the P2–P1↓P1’ (Gly–Gly↓Ala) position using the YESS–PSSC system. Our results demonstrated that Ulp1 was able to cleave Gly–Gly↓ motif-mutated substrates, indicating that the diglycine motif is not strictly required for Ulp1 cleavage. A structural-modeling analysis indicated that it is the special tapered active pocket of Ulp1 conferred the selectivity of small residues at the P1–P2 position of Smt3, such as Gly, Ala, Ser and Cys, and only which can smoothly deliver the scissile bond into the active site for cleavage. Meanwhile, the P1’ position Ala of Smt3 was found to play a vital role in maintaining Ulp1’s precise cleavage after the Gly–Gly motif and replacing Ala with Gly in this position could expand Ulp1 inclusivity against the P1 and P2 position residues of Smt3. All in all, our studies advanced the traditional knowledge of the SUMO protein, which may provide potential directions for the drug discovery of abnormal SUMOylation-related diseases.

The Interfacial Interactions of Glycine and Short Glycine Peptides in Model Membrane Systems

The interactions of amino acids and peptides at model membrane interfaces have considerable implications for biological functions, with the ability to act as chemical messengers, hormones, neurotransmitters, and even as antibiotics and anticancer agents. In this study, glycine and the short glycine peptides diglycine, triglycine, and tetraglycine are studied with regards to their interactions at the model membrane interface of Aerosol-OT (AOT) reverse micelles via ¹H NMR spectroscopy, dynamic light scattering (DLS), and Langmuir trough measurements. It was found that with the exception of monomeric glycine, the peptides prefer to associate between the interface and bulk water pool of the reverse micelle. Monomeric glycine, however, resides with the N-terminus in the ordered interstitial water (stern layer) and the C-terminus located in the bulk water pool of the reverse micelle.

Synthesis, Docking, Computational Studies, and Antimicrobial Evaluations of New Dipeptide Derivatives Based on Nicotinoylglycylglycine Hydrazide

Within a series of dipeptide derivatives (5–11), compound 4 was refluxed with d-glucose, d-xylose, acetylacetone, diethylmalonate, carbon disulfide, ethyl cyanoacetate, and ethyl acetoacetate which yielded 5–11, respectively. The candidates 5–11 were characterized and their biological activities were evaluated where they showed different anti-microbial inhibitory activities based on the type of pathogenic microorganisms. Moreover, to understand modes of binding, molecular docking was used of Nicotinoylglycine derivatives with the active site of the penicillin-binding protein 3 (PBP3) and sterol 14-alpha demethylase’s (CYP51), and the results, which were achieved via covalent and non-covalent docking, were harmonized with the biological activity results. Therefore, it was extrapolated that compounds 4, 7, 8, 9, and 10 had good potential to inhibit sterol 14-alpha demethylase and penicillin-binding protein 3; consequently, these compounds are possibly suitable for the development of a novel antibacterial and antifungal therapeutic drug. In addition, in silico properties of absorption, distribution, metabolism, and excretion (ADME) indicated drug likeness with low to very low oral absorption in most compounds, and undefined blood–brain barrier permeability in all compounds. Furthermore, toxicity (TOPKAT) prediction showed probability values for all carcinogenicity models were medium to pretty low for all compounds.

Recognition of the Diglycine C-End Degron by CRL2KLHDC2 Ubiquitin Ligase

Aberrant proteins can be deleterious to cells and are cleared by the ubiquitin-proteasome system. A group of C-end degrons that are recognized by specific cullin-RING ubiquitin E3 ligases (CRLs) has recently been identified in some of these abnormal polypeptides. Here, we report three crystal structures of a CRL2 substrate receptor, KLHDC2, in complex with the diglycine-ending C-end degrons of two early-terminated selenoproteins and the N-terminal proteolytic fragment of USP1. The E3 recognizes the degron peptides in a similarly coiled conformation and cradles their C-terminal diglycine with a deep surface pocket. By hydrogen bonding with multiple backbone carbonyls of the peptides, KLHDC2 further locks in the otherwise degenerate degrons with a compact interface and unexpected high affinities. Our results reveal the structural mechanism by which KLHDC2 recognizes the simplest C-end degron and suggest a functional necessity of the E3 to tightly maintain the low abundance of its select substrates.

C-terminal processing of GlyGly-CTERM containing proteins by rhombosortase in Vibrio cholerae

Vibrio cholerae and a subset of other Gram-negative bacteria, including Acinetobacter baumannii, express proteins with a C-terminal tripartite domain called GlyGly-CTERM, which consists of a motif rich in glycines and serines, followed by a hydrophobic region and positively charged residues. Here we show that VesB, a V. cholerae serine protease, requires the GlyGly-CTERM domain, the intramembrane rhomboid-like protease rhombosortase, and the type II secretion system (T2SS) for localization at the cell surface. VesB is cleaved by rhombosortase to expose the second glycine residue of the GlyGly-CTERM motif, which is then conjugated to a glycerophosphoethanolamine-containing moiety prior to engagement with the T2SS and outer membrane translocation. In support of this, VesB accumulates intracellularly in the absence of the T2SS, and surface-associated VesB activity is no longer detected when the rhombosortase gene is inactivated. In turn, when VesB is expressed without an intact GlyGly-CTERM domain, VesB is released to the extracellular milieu by the T2SS and does not accumulate on the cell surface. Collectively, our findings suggest that the posttranslational modification of the GlyGly-CTERM domain is essential for cell surface localization of VesB and other proteins expressed with this tripartite extension.

Identification and Isolation of Novel Sugar-Like RNA Protecting Materials: Glycylglycerins from Pluripotent Stem Cells

Pluripotent stem cells are a resourceful treasure box for regenerative medicine. They contain a large variety of novel materials useful for designing and developing new medicines and therapies directed against many aging-associated degenerative disorders, including Alzheimer's disease, Parkinson's disease, stroke, diabetes, osteoporosis, and cancers. Currently, identification of these novel stem cell-specific materials is one of major breakthroughs in the field of stem cell research. Particularly, since the discovery of induced pluripotent stem cells (iPSC) in year 2006, the methods of iPSC derivation further provide an unlimited resource for screening, isolating, and even producing theses novel stem cell-specific materials in vitro. Using iPSCs, we can now prepare high quality and quantity of pure stem cell-specific agents for testing their therapeutic functions in treating various illnesses. These newly found stem cell-specific agents are divided into four major categories, including proteins, saccharides, nucleic acids, and small molecules (chemicals). In this article, we herein disclose one of the methodologies for isolating and purifying glycylglycerins-a group of glycylated sugar alcohols that protect hairpin-like microRNA precursors (pre-miRNA) and some of tRNAs in pluripotent stem cells. In view of such a unique RNA-protecting feature, glycylglycerins may be used to preserve and deliver functional small RNAs, such as pre-miRNAs and small interfering RNAs (siRNA), into human cells for eliciting their specific RNA interference (RNAi) effects, which may greatly advance the use of RNAi technology for treating human diseases.

GlyGly-CTERM and rhombosortase: a C-terminal protein processing signal in a many-to-one pairing with a rhomboid family intramembrane serine protease

The rhomboid family of serine proteases occurs in all domains of life. Its members contain at least six hydrophobic membrane-spanning helices, with an active site serine located deep within the hydrophobic interior of the plasma membrane. The model member GlpG from Escherichia coli is heavily studied through engineered mutant forms, varied model substrates, and multiple X-ray crystal studies, yet its relationship to endogenous substrates is not well understood. Here we describe an apparent membrane anchoring C-terminal homology domain that appears in numerous genera including Shewanella, Vibrio, Acinetobacter, and Ralstonia, but excluding Escherichia and Haemophilus. Individual genomes encode up to thirteen members, usually homologous to each other only in this C-terminal region. The domain's tripartite architecture consists of motif, transmembrane helix, and cluster of basic residues at the protein C-terminus, as also seen with the LPXTG recognition sequence for sortase A and the PEP-CTERM recognition sequence for exosortase. Partial Phylogenetic Profiling identifies a distinctive rhomboid-like protease subfamily almost perfectly co-distributed with this recognition sequence. This protease subfamily and its putative target domain are hereby renamed rhombosortase and GlyGly-CTERM, respectively. The protease and target are encoded by consecutive genes in most genomes with just a single target, but far apart otherwise. The signature motif of the Rhombo-CTERM domain, often SGGS, only partially resembles known cleavage sites of rhomboid protease family model substrates. Some protein families that have several members with C-terminal GlyGly-CTERM domains also have additional members with LPXTG or PEP-CTERM domains instead, suggesting there may be common themes to the post-translational processing of these proteins by three different membrane protein superfamilies.

[Evaluation of the role of the peptide transport system in absorption of dipeptides in the rat small intestine in chronic experiments in vivo]

Hydrolysis and absorption of glycylgycine and glycyl-L-leucine as well as absorption of glycine and leucine were studied in chronic experiments on rats with their isolated small intestine loop. Values of the true kinetic constants (with taking into account effect of the preepithelial layer) were determined to be as follows: 1) Kt = 46.7 +/- 4.0 and 2.15 +/- 0.59 mM; Jmax = 0.74 +/- 0.15 and 0.16 +/- 0.03 micromol x min(-1) x cm(-1) (for the transport of free glycine and leucine, respectively); 2) Kt = 4.4 +/- 0.6 and 4.8 +/- 0.9 mM, Jmax = 0.24 +/- 0.02 and 0.23 +/- 0.02 micromol x min(-1) x cm(-1) (for the transport of glycylgycine and glycyl-L-leucine, respectively); 3) Km = 5.4 +/- 1.0 and 38.2 +/- 4.4 mM, Vmax = 0.09 +/- 0.02 and 0.24 +/- 0.07 micromol x min(-1) x cm(-1) (for membrane hydrolysis of these dipeptides, respectively). According to our calculations, in the wide range of the initial glycylgycine concentrations (2.5-40 mM) the part of the peptide component in its total absorption accounts for 0.77-0.80. In the case of glycyl-L-leucine the part of the peptide component in the total glycine absorption decreases from 0.89 to 0.84, while in the total leucine absorption--from 0.86 to 0.71, the initial dipeptide concentration rising from 5 to 40 mM. The obtained results show that the peptide component prevails in absorption of the studied dipeptides in the rat small intestine, but its role is much lesser that what many authors believe. In the case of glycyl-L-leucine, the peptide component can achieve saturation in the range of high substrate concentrations, its part decreasing essentially to become compared with absorption of free amino acids formed as a result of the dipeptide membrane hydrolysis.

In vivo evaluation of cysteine-based chelators for attachment of 99mTc to tumor-targeting Affibody molecules

Affibody molecules present a new class of affinity proteins, which utilizes a scaffold based on a 58-amino acid domain derived from protein A. The small (7 kDa) Affibody molecule can be selected to bind to cell-surface targets with high affinity. An Affibody molecule (ZHER2:342) with a dissociation constant (Kd) of 22 pM for binding to the HER2 receptor has been reported earlier. Preclinical and pilot clinical studies have demonstrated the utility of radiolabeled ZHER2:342 in imaging of HER2-expressing tumors. The small size and cysteine-free structure of Affibody molecules enable complete peptide synthesis and direct incorporation of radionuclide chelators. The goal of this study was to evaluate if incorporation of the natural peptide sequences cysteine-diglycine (CGG) and cysteine-triglycine (CGGG) sequences would enable labeling of Affibody molecules with 99mTc. In a model monomeric form, the chelating sequences were incorporated by peptide synthesis. The HER2-binding affinity was 280 and 250 pM for CGG-ZHER2:342 and CGGG-ZHER2:342, respectively. Conjugates were directly labeled with 99mTc with 90% efficiency and preserved the capacity to bind specifically to HER2-expressing cells. The biodistribution in normal mice showed a rapid clearance from the blood and the majority of organs (except kidneys). In the mice bearing SKOV-3 xenografts, tumor uptake of 99mTc-CGG-ZHER2:342 was HER2-specific and a tumor-to-blood ratio of 9.2 was obtained at 6 h postinjection. Gamma-camera imaging with 99mTc-CGG-ZHER2:342 clearly visualized tumors at 6 h postinjection. The results show that the use of a cysteine-based chelator enables 99mTc-labeling of Affibody molecules for imaging.

[The influence of protein starvation on hydrolytic and transport characteristics of the rat small intestine in chronic experiments]

Time dynamics of maltose, glycylglycine, glucose, and glycine hydrolysis and absorption in isolated loop of the small intestine was studied in chronic experiments on Wistar rats (group 1) after their transition from the standard diet to the protein-free one with enhanced content of carbohydrates. During protein starvation, there were different changes in the rates of glucose and glycine absorption, and glycylglycine hydrolysis and absorption in isolated intestinal loop, but to the end of the 2nd week they returned to the initial levels (for glucose and glycylglycine) or increased (for glycine). The rates of maltose hydrolysis and derived glucose absorption remained at the initial levels for the first days of protein starvation, decreased on the 5th day, and did not change afterwards. Maltase, alkaline phosphatase, and amino peptidase M activities, determined in homogenates of the small intestinal mucosa (per g of the tissue) after 2 weeks of protein starvation, were lower in the rats of group 1 in comparison with the rats of group 2, kept on the standard diet. Thus, under protein deficiency the hydrolytic and absorptive capacities of the small intestine correspond to both ingested food composition, and body requirements.

The ubiquitin binding domain ZnF UBP recognizes the C-terminal diglycine motif of unanchored ubiquitin

Ubiquitin binding proteins regulate the stability, function, and/or localization of ubiquitinated proteins. Here we report the crystal structures of the zinc-finger ubiquitin binding domain (ZnF UBP) from the deubiquitinating enzyme isopeptidase T (IsoT, or USP5) alone and in complex with ubiquitin. Unlike other ubiquitin binding domains, this domain contains a deep binding pocket where the C-terminal diglycine motif of ubiquitin is inserted, thus explaining the specificity of IsoT for an unmodified C terminus on the proximal subunit of polyubiquitin. Mutations in the domain demonstrate that it is required for optimal catalytic activation of IsoT. This domain is present in several other protein families, and the ZnF UBP domain from an E3 ligase also requires the C terminus of ubiquitin for binding. These data suggest that binding the ubiquitin C terminus may be necessary for the function of other proteins.

Catalytic transformations with copper-metalated diglycine conjugates

A series of copper-metalated, water-soluble bis-diglycine conjugates were synthesized and characterized through spectroscopic methods. These conjugates were evaluated for the cleavage of phosphodiester substrates, supercoiled plasmid relaxation in the presence of co-oxidants, and for the oxidation of a diphenolic substrate, 2,6-dimethoxyphenol. Appreciable rate enhancements were observed for these reactions and the oxidative nucleolytic cleavage activity and phenol oxidative coupling was presumably manifested via formation of reactive oxygen species.

Effect of Dipeptides on the Growth of Oenococcus oeni in Synthetic Medium Deprived of Amino Acids

Oenococcus oeni has numerous amino acid requirements for growth and dipeptides could be important for its nutrition. In this paper the individual or combined effect of dipeptides on growth of O. oeni X2L in synthetic media deficient in one or more amino acids with L-malic acid was investigated. Utilization of dipeptides, glucose, and L-malic acid was also analyzed. Dipeptides were constituted by at least one essential amino acid for growth. Dipeptides containing two essential amino acids, except leucine, had a more favorable effect than free amino acids on the growth rate. Gly-Gly was consumed to a greater extent than Leu-Leu and a rapid exodus of glycine to the extracellular medium accompanied it. The microorganism could use glycine in exchange for other essential amino acids outside the cell, favoring growth. In the presence of Leu-Leu, the increase in glucose consumption rate could be related to the additional energy required for dipeptide uptake.

Modification of the furanacryloyl-l-phenylalanylglycylglycine assay for determination of angiotensin-I-converting enzyme inhibitory activity

Angiotensin-I-converting enzyme (ACE, EC 3.4.15.1) plays a central role in the regulation of blood pressure in man. The objective of this study was to evaluate and modify the furanacryloyl-L-phenylalanylglycylglycine (FAPGG) assay method for quantification of ACE activity. The fixed time conditions developed for assay of ACE activity were as follows: 0.8 mM FAPGG, 175 + or - 10 units l(-1) ACE, incubation at 37 degrees C for 30 min and enzyme inactivation with 100 mM ethylenediaminetetra-acetic acid (EDTA). Hydrolysis of FAPGG to FAP and GG was quantified by measuring the decrease in absorbance at 340 nm. It was shown that increasing the level ACE activity in the assay from 155 to 221 + or - 15 units l(-1) resulted in a corresponding increase in the apparent IC(50) value for Captopril from 9.10 to 39.40 nM. Similar trends in the apparent IC50 values for a whey protein hydrolysate were obtained. The results demonstrate the requirement for carefully controlling ACE activity levels in the assay in order to obtained comparable and reproducible values for the inhibitory potency of ACE inhibitors.

Evidence for the pro-oxidant effect of gamma-glutamyltranspeptidase-related enzyme

It has been previously reported that the metabolism of reduced glutathione (GSH) by gamma-glutamyltranspeptidase (GGT) in the presence of chelated metals leads to free radical generation and lipid peroxidation (LPO). The present study demonstrates for the first time that an established cell line expressing GGT-rel, a human GGT-related enzyme, metabolizes extracellular GSH to cysteinylglycine (CysGly) in a time-dependent manner when cells were incubated in a medium containing 2.5 mM GSH and 25 mM glycylglycine. Supplementation with 150-165 microM Fe(3+)-EDTA resulted in a reactive oxygen species (ROS) generation process. The resulting data showed a significantly higher level (7.6-fold) of ROS production in the GGT-rel positive cells in comparison with the GGT-rel negative control cells. CysGly and Cys, but not GSH, were responsible for the observed ROS production, as we confirmed by measuring the same process in the presence of Fe(3+)-EDTA and different thiols. A higher iron reduction and an increased LPO level determined by malondialdehyde HPLC measurement were also found in GGT-rel-overexpressing cells compared to GGT-rel negative cells. Our data clearly indicate that in the presence of iron, not only GGT, but also GGT-rel has a pro-oxidant function by generation of a reactive metabolite (CysGly) and must be taken into account as a potential physiopathological oxidation system.

Role of an interdomain Gly-Gly sequence at the regulatory-substrate domain interface in the regulation of Escherichia coli. D-3-phosphoglycerate dehydrogenase

The regulatory and substrate binding domains of D-3-phosphoglycerate dehydrogenase (PGDH, EC 1.1.1.95) from Escherichia coli are connected by a single polypeptide strand that contains a Gly-Gly sequence approximately midway between the domains. The potential flexibility of this sequence and its strategic location between major domain structures suggests that it may function in the conformational change leading from effector binding to inhibition of the active site. Site-directed mutagenesis of this region (Gly-336-Gly-337) supports this hypothesis. When bulky side chains were substituted for the glycines at these positions, substantial changes in the ability of serine to inhibit the enzyme were seen with little effect on the activity of the enzyme. The effect of these substitutions could be alleviated by placing a new glycine residue at position 335, immediately flanking the original glycine pair. On the other hand, substituting a glycine at position 338 revealed a critical role for the side chain of Arg-338. This residue may function in stabilizing the conformation about the Gly-Gly turn, resulting in a specific orientation of the adjacent domains relative to each other. Rotation about the phi or psi bonds of either Gly-336 or Gly-337 would have a profound effect on this orientation. The data are consistent with this as a role for the Gly-Gly sequence between the regulatory and substrate binding domains of PGDH.

Determination of chiral catabolites from S-[2-carboxyl-1-(1H-imidazol-4-yl)ethyl]glutathione, a proposed metabolite of L-histidine, by capillary electrophoresis]

A new method for simultaneous determination of two diastereomers in each of S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-L-cysteine (I) and N-¿S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-L-cysteinyl¿glycine (II) was developed by electrophoresis using a neutral coated capillary with a separation buffer, pH 6.00, containing 80 mM hydroxypropyl-beta-cyclodextrin at a field strength of 500 V cm-1 at 20 degrees C. This method was applied to establishment of a catabolic pathway from S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]glutathione (III) to compound I. Incubation of either of compound II diastereomers as an enzyme substrate with rat kidney homogenate in a phosphate buffer, pH 7.4, resulted in a formation of compound I only having correspondent configurations on asymmetric carbon atoms of its molecule with those of the substrate, i.e., no occurrence of isomerization in the catabolism. Additionally, little difference in action as the substrate between two diastereomers of compound II was found. When an equimolar mixture of two diastereomers of compound III was allowed to react with the homogenate in the presence of glycylglycine, two diastereomers of compound II were formed in the same yield with each other and then these were catabolized gradually to both isomers of compound I. These results suggest that compound II is a metabolic intermediate for the formation of compound I from compound III, and that little variation in reactivities of two diastereomers of compound III as well as compound II with enzymes is given by the difference in stereoisomerism of asymmetric carbon atoms on their molecules.

Metabolism of diglycine and triglycine by non-filtering kidneys

We have studied the metabolism of diglycine and triglycine in the isolated non-filtering rat kidney. Kidneys from adult male Wistar Kyoto rats weighing 250-350 g were perfused with Krebs-Henseleit solution containing either 1 mM diglycine or triglycine. The analysis of the peptide residues and their components was performed using an amino acid microanalyzer utilizing ion exchange chromatography. Diglycine was degraded to a final concentration of 0.09 mM after 120 min (91%); this degradation occurred predominantly during the first hour, with a 56% reduction of the initial concentration. The metabolism of triglycine occurred similarly, with a final concentration of 0.18 mM (82%); during the first hour there was a 67% reduction of the initial concentration of the tripeptide. Both peptides produced glycine in increasing concentrations, but there was a slightly lower recovery of glycine, suggesting its utilization by the kidney as fuel. The hydrolysis of triglycine also produced diglycine, which was also hydrolyzed to glycine. The results of the present study show the existence of functional endothelial or contraluminal membrane peptidases which may be important during parenteral nutrition.

On the usefulness of glycylglycine in hemodialysis and peritoneal dialysis solutions

This article reviews current knowledge on the usefulness of glycylglycine in preparing single stable hemodialysis (HD) and peritoneal dialysis (PD) solutions containing bicarbonate. The coexistence of bicarbonate and glycylglycine in a dialysis solution renders it a potent, stable buffer in which the well known reactions between bicarbonate and calcium and magnesium, and the subsequent formation of insoluble neutral calcium and magnesium carbonate salts, are avoided. Single stable bicarbonate-glycylglycine (BiGG) solutions for HD and PD have been successfully prepared and studied, both experimentally and clinically. These studies have demonstrated the advantages of BiGG solutions in terms of simplicity, stability, convenience, tolerance, biocompatibility, protection of the peritoneum, and higher ultrafiltration, compared to standard acetate or lactate solutions, and on-line prepared bicarbonate solutions. Progressive accumulation of glycylglycine or glycine, even after prolonged use, side effects, or signs of toxicity were not observed. In conclusion, BiGG solutions ensure a physiologic dialysis both from the theoretic and practical points of view.

Glycylcyclines bind to the high-affinity tetracycline ribosomal binding site and evade Tet(M)- and Tet(O)-mediated ribosomal protection

N,N-dimethylglycylamido (DMG) derivatives of 6-demethyl-6-deoxytetracycline and doxycycline bind 5-fold more effectively than tetracycline to the tetracycline high-affinity binding site on the Escherichia coli 70S ribosome, which correlates with a 10-fold increase in potency for inhibition of E. coli cell-free translation. The potencies of DMG-doxycycline and DMG-6-demethyl-6-deoxytetracycline were unaffected by the ribosomal tetracycline resistance factors Tet(M) and Tet(O) in cell-free translation assays and whole-cell bioassays with a conditional Tet(M)-producing E. coli strain.

Selective effect of zinc on uphill transport of oligopeptides into kidney brush border membrane vesicles

Based on the involvement of zinc in hydrolysis of peptides, we hypothesized that Zn2+ may also play a role in peptide transport. To investigate this hypothesis, kidney brush border membrane vesicles (BBMV) were incubated for 30 min with different concentrations of ZnSO4 before use in uptake studies. This incubation increased by twofold the overshoot uptake of 3H-Gly-L-Gln, D-Leu-125I-Tyr and 3H-cephalexin (all high-affinity substrates for the oligopeptide/H+ symporter) without affecting passive and/or facilitated diffusion of these substrates. Zinc had no effect on the uptake of either glutamine or glucose by kidney BBMV. Among a group of metal ions (cobalt, iron, copper, cadmium, and manganese), only manganese and copper substantially stimulated the activity of the oligopeptide/H+ symporter. DTPA (a complexing agent) inhibited dipeptide uptake, which was reversed by the addition of zinc to the BBMV. Zinc treatment of BBMV reduced the EC50 value of inhibition of 3H-Gly-L-Gln uptake by unlabeled Gly-L-Gln by twofold (90 +/- 8 vs. 45 +/- 4 microM). Similarly, zinc treatment of BBMV reduced the EC50 value for inhibition of D-Leu-125I-Tyr uptake by bestatin from 80 +/- 4 to 40 +/- 3 mM. In conclusion, the data show that zinc has a selective effect on transport of nutrients into kidney BBMV. It stimulates uphill transport of oligopeptides by a modification of their affinity for the binding site of the membrane transporter.

Dipeptide transport in barley mesophyll vacuoles

The transport of [14C]glycyl-glycine (Gly-Gly) across the tonoplast of isolated barley vacuoles has been characterized. Uptake of the dipeptide Gly-Gly into barley mesophyll vacuoles was strongly increased by the addition of ATP, while Mg2+ inhibited the ATP-dependent fluxes. Inhibition of the vacuolar proton pump by bafilomycin or dissipation of the delta pH had no effect on the ATP-dependent Gly-Gly uptake. Only the non-hydrolysable ATP analogue 5'-adenylylimidodiphosphate could partially substitute for ATP; ADP, GTP and UTP had no effect. Transport of Gly-Gly was saturable exhibiting an apparent Km of 49 +/- 5 mM. Uptake was inhibited by the sulphydryl reagents N-ethylmaleimide and p-chloromercuribenzenesulphonic acid. When present at 30 mM, various dipeptides as well as tri-glycine inhibited Gly-Gly (10 mM) uptake by 30-50%, whereas 5 mM phenylalanine was able to inhibit Gly-Gly uptake almost completely. Comparison with published data suggests that Gly-Gly is transferred across the tonoplast by the same system as several amino acids and inorganic ions.

Comparison of kinetic property between human seminal and renal gamma-glutamyltransferase

The initial-velocity kinetics, optimal pH, acceptor specificity and the influence of metal ions, EDTA and urea were studied on the human seminal gamma-glytamyltransferase (GGT) in comparison with the human renal GGT. The activity was measured with glycylglycine as an acceptor and with gamma-glutamyl-4-nitroanilide or gamma-glutamyl-3-carboxy-4-nitroanilide as a donor. Because the double-reciprocal plots showed paralled lines, the reaction of seminal GGT proceeds in nonsequence (Ping Pong Bi Bi) mechanism. The acceptor Michaelis constants for the seminal GGT were about 2 times higher than those for the renal enzyme with gamma-glutamyl-3-carboxy-4-nitroanilide as well as gamma-glutamyl-4-nitroanilide as donors, which the donor michaelis constants for seminal GGT were very similar to those for renal enzyme. The optimal pH and pK values were 8.2-8.6 and about 7.7, respectively. There was little difference in the specificity for various acceptors between the seminal and renal enzyme. Glycylglycylglycine was an effective acceptor other than glycylglycine, showing 80% of the activity with glycylgycine. Various substrates including metal ions tested were practically neither inhibitory nor stimulatory for seminal and renal GGTs.

Epithelial properties of human intestinal Caco-2 cells cultured in a serum-free medium

Human intestinal Caco-2 cells were cultured under serum-free conditions on an insoluble collagen and FCS matrix (Caco-2-SF), and a comparison was made between several characteristics of Caco-2 and Caco-2-SF cells. Their morphological appearance was identical. Slight differences were found in cell growth and expression of brush border enzymes between Caco-2 and Caco-2-SF cells. Similar levels of activity of Gly-Gly transport were expressed in both types of cell. Caco-2 cells cultured on permeable filters showed high transepithelial electrical resistance (TEER), indicating the high monolayer integrity. The transepithelial transport activity for glucose, alanine and Gly-Gly was detected by measuring the change in short-circuit current (delta Isc) after adding each of these nutrients to the apical chamber. In Caco-2-SF cells, such parameters as TEER and delta Isc were reduced drastically, suggesting that the monolayer integrity and cell polarity that are important for transepithelial transport were not attained. These parameters, however, could be restored by adding FCS or by milk whey. The result suggested that FCS and milk whey contain factors which regulate the formation of the tight junctions and, consequently, the development of cell polarity. Thus the Caco-2-SF cell-culture system will provide a useful model for studying factors which regulate the intestinal transepithelial transport functions.

H+/glycyl-glycine cotransport in eel intestinal brush-border membrane vesicles: studies with the pH-sensitive dye Acridine orange

Monitoring the fluorescence quenching of the pH-sensitive dye Acridine orange, proton accumulation in the presence of an inside-negative transmembrane potential was measured in eel (Anguilla anguilla) intestinal brush-border membrane vesicles. It was demonstrated that the proton accumulation was specifically increased by the presence of the dipeptide glycyl-glycine in the extravesicular space, showing saturation kinetics at increasing dipeptide concentrations and was specifically inhibited by diethylpyrocarbonate. Data reported suggest the presence of an electrical-potential-dependent H+/glycyl-glycine cotransport system in the eel intestinal brush-border membrane vesicles.

Protein-peptide interactions as probed by tryptophan fluorescence: serum albumins and enkephalin metabolites

Binding of Leu-enkephalin and the enkephalin metabolite, tyrosine-glycine-glycine (TGG), to bovine serum albumin (BSA) was studied as a model to investigate protein peptide interactions. TGG and Leu-enkephalin quench the tryptophyl fluorescence of BSA. Stern-Volmer quenching constants were typically in the range of 40 to 300 M-1, depending on the experimental conditions. The addition of Cu(II) or Ni(II) did not change the quenching constant, indicating that TGG does not compete for the metal binding sites on BSA. From fluorescence quenching studies with TGG, tyrosyl-glycine, tyrosine and glycyl-glycine, it was concluded that the presence of the tyrosine residue is required for the observed quenching. The phenolic group in tyrosine accounted for the quenching mechanism because phenol was efficient in quenching BSA fluorescence, whereas phenylalanine had no detectable effect. A large solvent isotope effect on the quenching constant of phenol and TGG with BSA strongly suggests an active role of the -OH functionality in the quenching mechanism.

Developmental changes in the activity of membrane-bound gamma-glutamyl transpeptidase and in the sialylation of synaptosomal membranes from the chick embryonic brain

gamma-Glutamyl transpeptidase (GGT) is a membrane-bound sialoglycoprotein. The developmental changes in GGT activity and in sialic acid content were determined in a crude synaptosomal membrane fraction from the cerebral hemispheres of the chick embryo between days 11 and 19 of incubation. The GGT activity increased almost eightfold during the examined developmental period, while sialic acid content rose significantly only between days 11 and 15. Cortical administered on day 13 significantly increased GGT activity. On the other hand, the content of membrane bound sialic acid was not substantially affected. The value of the GGT apparent Michaelis constant (Kmapp) for gamma-glutamyl-p-nitroanilide in the presence of 20 mmol.l-1 glycylglycine was 1.5 mmol.l-1 and cortisol did not influence it. However, Vmax was increased by this hormone. The affinity of GGT to concanavalin A (ConA) did not change during development. Neither the administration of cortisol nor neuroaminidase treatment had any effect on the interaction of GGT with ConA. Desialylation of crude synaptosomal fraction did not change GGT activity. The results presented here suggest no developmental nor functional relationship between the activity of GGT and the level of sialylation in synaptosomal membranes from the cerebral hemispheres of the chick embryo.

Active transport of amino acids by gamma-glutamyl transpeptidase through Caco-2 cell monolayers

The possible role of the gamma-glutamyl cycle in the transport of amino acids, using the Caco-2 cell monolayer as an in vitro model of the small intestine, has been investigated. The transport of [2-3H]glycine and [2-3H]glycylglycine through the Caco-2 monolayer has been shown to occur by two modes of action. Active transport is unidirectional from apical to basolateral region and is a carrier mediated system. The enzyme gamma-glutamyl transpeptidase seems to be involved in this process, since when the enzyme is inhibited, the active transport is also inhibited. However transport still takes place, and this occurs by a slower non-active process, which is bidirectional and is mediated by passive diffusion. The rate of transport of [2-3H]glycylglycine and [2-3H]glycine were 585 (+/- 24) and 287 (+/- 16) pmolcm-2min-1 respectively, while the non-active transport takes place at 87 (+/- 6) pmolcm-2min-1. Thus, amino acid translocation in Caco-2 cells is shown to occur by two methods, one of which involves the gamma-glutamyl cycle.

Comparison of transport characteristics of amino beta-lactam antibiotics and dipeptides across rat intestinal brush border membrane

The transport characteristics of amino beta-lactam antibiotics, ampicillin and cephradine, have been examined and compared with that of glycylglycine using brush border membrane vesicles isolated from rat small intestine. The initial rate of glycylglycine uptake was markedly stimulated in the presence of an inward H+ gradient compared with the uptake rates in the absence of an H+ gradient. With the same H+ gradient the stimulation of cephradine uptake was lower and ampicillin uptake was not altered. Cephradine uptake, however, was greater than that of glycylglycine in both vesicular conditions ((pH)i greater than (pH)o and (pH)i = (pH)o). Inhibitory effects of dipeptides, ampicillin and cephradine on the initial uptake of glycylglycine were also examined. Glycylglycine uptake was significantly decreased in the presence of L-phenylalanylglycine or carnosine. Ampicillin and cephradine did not alter the uptake of glycylglycine. These results suggest that the contribution of the inward H+ gradient to the permeation of ampicillin, cephradine and glycylglycine across the rat small intestinal brush border membranes is different for each of the substances examined.

Effect of chlorpromazine on the permeability of beta-lactam antibiotics across rat intestinal brush border membrane vesicles

The effect of chlorpromazine on the membrane permeability of beta-lactam antibiotics (benzylpenicillin, ampicillin, cephradine and cephalexin) and actively transported substances (glycylglycine and D-glucose) has been studied using rat intestinal brush border membrane vesicles. Except for cephalexin, the initial uptakes at 25 degrees C of these antibiotics were significantly enhanced in the presence of chlorpromazine. In contrast, the transport of glycylglycine and D-glucose was significantly inhibited. These results suggest that the two groups, drugs and actively transported substances, have a different permeation process. The effect of chlorpromazine concentration on membrane lipid fluidity, as assessed by the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-anilino-8-naphthalene sulphonate (ANS), was also examined. The fluorescence polarization of ANS decreased with increasing concentration of chlorpromazine, while that of DPH increased suggesting an increase of membrane surface fluidity might affect the permeation of beta-lactam antibiotics and actively transported substances in a different manner.

Metabolism of dipeptides and their constituent amino acids by liver, gut, kidney, and muscle

Oligopeptides may enter the bloodstream from endogenous and exogenous sources. Using an organ-balance technique in conscious dogs, we investigated the role of individual organs in removal of two model oligopeptides (glycylleucine and glycylglycine) from plasma under steady-state conditions. Despite an identical infusion rate, arterial concentration of glycylglycine was twofold greater than that of glycylleucine. This appeared to be a result of greater fractional extraction of glycylleucine than glycylglycine by organs. Although all of the organs examined participated in removal of dipeptides from plasma, their roles varied. Liver, kidney, muscle, and gut accounted for the disappearance of 25, 24, 12, and 10% of the infused amount of glycylleucine, respectively. With glycylglycine as the substrate, disappearance across kidney accounted for 37% of the infused amount, whereas muscle, liver, and gut accounted for 18, 15, and 11%, respectively. Finally, we investigated glycine and leucine balances across organs with infusion of these amino acids in free and dipeptide forms. Glycine and leucine balances were uniquely more positive across muscle during the infusion of glycylleucine than the corresponding amino acid mixture. The possible mechanisms included release of products of glycylleucine hydrolysis by all organs except muscle. We conclude that molecular structure influences the organ extraction of dipeptides; if extraction, particularly by the liver, is not sufficiently rapid, kidney assumes a greater role than other organs in dipeptide removal from plasma.

Characteristics of transmural potential changes associated with the proton-peptide co-transport in toad small intestine

1. Ionic dependence and kinetic properties of the peptide-evoked potentials across everted toad intestine were investigated with eighteen dipeptides and four tripeptides. All peptides evoked saturable increases in the mucosal negativity regardless of the presence of Na+. 2. The peptide-evoked potentials recorded in the absence of Na+ were sensitive to external pH (pHo); lowering pHo from 7.4 to 6.5 and 5.5 caused stepwise increases in their amplitude. 3. Loading epithelial cells with 9-aminoacridine or acetate caused a significant increase or decrease in amplitude of the Gly-Gly-evoked potential, suggesting intracellular alkalinization or acidification also has a great influence on the peptide-evoked potential. 4. Kinetically, Na+-independent peptide-evoked potentials conformed to simple Michaelis-Menten kinetics, and lowering pHo caused a decrease of the half-saturation concentration (Kt) for Gly-Gly without changing the maximum potential difference increase. Similar affinity-type kinetic effect was also seen for Gly-Gly influx. 5. Simultaneous measurements of Gly-Gly-induced increase in short-circuit current and Gly-Gly influx revealed that the coupling ratio of H+ and Gly-Gly flows was 1.78 +/- 0.12, suggesting the stoichiometry of the H+-peptide co-transport being 2:1. 6. Kinetic analyses of the peptide-evoked potentials indicated that all glycyl-dipeptides tested (Gly-Gly, Gly-Pro, Gly-Sar, Gly-Leu, Gly-Phe) and other dipeptides (Ala-Ala, Ala-Phe, Phe-Ala) shared a common carrier. Gly-Gly-Gly and Ala-Ala-Ala were also found to share the same carrier, while Phe-Phe, Leu-Leu and Phe-Leu appeared to be transported by a different carrier. 7. Kt values for di- and tripeptides, which apparently shared a common carrier, fell in a narrow range (0.5-2.2 mM). There was no clear correlation between 1/Kt value and molecular weight.

Substrate recognition of isopeptidase: specific cleavage of the epsilon-(alpha-glycyl)lysine linkage in ubiquitin-protein conjugates

The structural chromatin protein A24 (uH2A) is a conjugate of histone H2A and a non-histone protein, ubiquitin. Eukaryotic cells contain an enzyme, generically termed isopeptidase, which can cleave A24 stoichiometrically into H2A and ubiquitin in vitro. Isopeptidase, free of proteinase activity, has been partially purified from calf thymus by ion-exchange chromatography, gel filtration and affinity chromatography, and analyzed for its substate specificity. There are three major types of isopeptide bonds besides the epsilon-(alpha-glycyl)lysine bond between H2A and ubiquitin; namely, the disulfide bridge, the aldol and aldimide bonds and the epsilon-(gamma-glutamyl)lysine crosslink. Under conditions where A24 was completely cleaved into H2A and ubiquitin, none of these naturally occurring isopeptide bonds was cleaved by isopeptidase. Furthermore, the bonds formed in vitro by transglutaminase reaction between casein and putrescine, through the gamma-NH2 of glutamine residue and the NH2 of putrescine, were not cleaved by the enzyme. The enzyme also failed to cleave the glycyl-lysyl and other orthodox peptide linkages within proteins. Among various proteins examined, the substrates for isopeptidase reaction were confined to conjugates between ubiquitin and other proteins, formed through epsilon-(alpha-glycyl)lysine bonds. Since ubiquitin released by isopeptidase is re-usable for an ATP-dependent conjugation with other proteins, its carboxyl terminal -Gly-Gly-COOH most likely is preserved intact, and is not blocked. These results suggest that isopeptidase specifically recognizes and cleaves the epsilon-(alpha-glycyl)lysine bond. A possible biological significance of this enzyme is discussed.

Partial purification and properties of gamma-glutamyltranspeptidase from mycelia of Morchella esculenta

Three gamma-glutamyltranspeptidase (enzymes I, II and III) were partially purified from the cell free extracts of the cultured mycelia of Morchella esculenta Fr. The molecular masses of enzymes were 155,000 (I), 219,000 (II) and 102,000 (III). All of them catalyzed both hydrolysis and transpeptidation of various gamma-glutamyl compounds. gamma-L-Glutamyl-cis-3-amino-L-proline occurring in the cultured mycelia of this fungus was a good substrate for both reactions. Km values for hydrolysis were in the order of 10(-4) to 10(-5) M, and those for transpeptidation were in the order of 10(-2) to 10(-4) M. The enzymes were inhibited by a gamma-glutamyltranspeptidase inhibitor, L-serine plus borate.

Proton gradient-coupled uphill transport of glycylsarcosine in rabbit renal brush-border membrane vesicles

An inward-directed proton gradient energizes the transport of intact glycylsarcosine against a concentration gradient in rabbit renal brush-border membrane vesicles. Dissipation of the proton gradient abolishes the uphill transport. Generation of an inside-negative membrane potential nearly doubles the intravesicular concentration of the dipeptide at the peak of the overshoot without altering the equilibrium value. These data provide direct evidence for peptide-proton cotransport in the renal brush-border membrane.

Kinetic assay of gamma-glutamyltransferase with use of bilirubin oxidase as a coupled enzyme

We studied the kinetic measurement of gamma-glutamyltransferase (EC.2.3.2.2), coupling the reaction with that catalyzed by bilirubin oxidase (EC 1.3.3.5), which oxidizes and combines a phenylenediamine derivative with an aniline derivative to produce a green pigment. We measured the formation of the pigment kinetically (at lambda max745 nm, epsilon = 75 000 L mol-1 cm-1), with L-gamma-glutamyl-N-hydroxyethylaminoanilide as substrate and N-ethyl-N-hydroxy-3-sulfopropyl)-m-toluidine as a the coupling derivative. The within-run CV for measuring this reaction in samples of normal sera was 2.4%. A calibration plot of the change in absorbance per minute vs enzyme activity concentration showed good proportionality in the range of 0-1300 U/L. The results of this assay correlated well (r = 0.995) with those of the Boehringer method, in which L-gamma-glutamyl-3-carboxy-4-nitroanilide is the substrate. This new, highly sensitive procedure may be adapted to other assays involving phenylenediamine derivates as synthetic substrates.

Mutual effects of amino-beta-lactam antibiotics and glycylglycine on the transmural potential difference in the small intestinal epithelium of rats

The transport mechanism of amino-beta-lactam antibiotics across in vitro rat ileum was examined using the electrophysiological technique in comparison with that of dipeptides. The changes in the transmural potential difference (PDt) induced by a series of amino-beta-lactam antibiotics were correlated with the absorption percentage of these antibiotics from the in situ rat intestinal loops. On the contrary, beta-lactam antibiotics without alpha-amino group such as dicloxacillin, methicillin and cefazolin did not induce such a stable change of PDt. The changes in PDt induced by cyclacillin (ACPC), cefadroxil (CDX) and glycylglycine (Gly-Gly) became saturable when the concentration of the substances increased. The half saturation concentration for ACPC, CDX, and Gly-Gly estimated from the changes in PDt was nearly identical with that determined from influx of the substrates in the everted intestinal sacs. The mutual inhibition between amino-beta-lactam antibiotics and Gly-Gly was observed in their induced PDts. The changes in PDt induced by amino-beta-lactam antibiotics were independent of those of glucose, glycine, and cefazolin. By the removal of Na+ from the mucosal solution, the PDt decreased one-fifth of the PDt induced in the presence of Na+. These results suggest that amino-beta-lactam antibiotic-induced PDt relates to the Na+ ion fluxes as reported for dipeptides.

[Application of a potential difference to evaluate the absorptive faculty in the small intestine. The change of the transmural resistance and the transport system during post-natal development]

Presently there is no effective method for evaluating the intestinal absorption of sugar, amino acid and small peptide. Since the transmural potential difference (delta PD) is generated immediately when sugar, amino acid or small peptide are absorbed in the small intestine, we tried to utilize this potential difference for the evaluation of absorptive faculty. The delta PD is the product of influx and electrical transmural resistance. To evaluate the intestinal absorptive faculty by the delta PD it is necessary that the electrical resistance of the small intestine does not change throughout the life time and that sugars, amino acids and peptides are transported actively. In guinea pig, the electrical resistance of the small intestine was examined in postnatal development in vitro. Transport systems of sugars amino acid and peptide were also investigated. Through the entire life the electrical resistance of the small intestine remained at almost the same value and sugars and amino acid were completely transported actively from the birth. But small peptide was transported actively after the period of weanling. Evaluation of intestinal aborptive faculty of sugars, amino acids and small peptides is considered to be possible by the transmural potential difference.

Effect of hydrogen ion-gradient on carrier-mediated transport of glycylglycine across brush border membrane vesicles from rabbit small intestine

Glycylglycine (Gly-Gly) transport across rabbit small intestinal brush border membrane vesicles was studied in the presence and absence of a Na+ gradient or a pH gradient. The transport was found to be entirely independent of Na+ but significantly stimulated by lowering extravesicular pH (pHo). The maximum stimulation was seen at pHo 5.5, where the uptake rate was about 2-times higher than the control value. FCCP, a protonophore, abolished the stimulating effect of low pHo, and low pHo conditions without a pH gradient did not stimulate the uptake rate. Overshoot uptake of Gly-Gly was observed when a pH gradient of 2 pH units was imposed across the vesicular membrane. Valinomycin-induced inside-negative K+ diffusion potential also had a stimulating effect on the uptake, and fluorescence measurements of vesicular suspensions containing diS-C3-(5) revealed the occurrence of depolarization of the vesicular membranes when Gly-Gly was added to the suspensions. Kinetic study showed that a pH gradient caused a decrease of Kt for Gly-Gly without affecting Vmax. All the data obtained indicate that Gly-Gly transport is independent of Na+, dependent on a H+ gradient, and electrogenic, suggesting the mechanism of cotransport with H+.

The characteristics of carnosine transport and carnosine-induced electrical phenomena by the everted intestine of guinea pig

The properties of carnosine (Car) and glycylglycine (Gly-Gly), transported across the mucosal border, were studied in isolated guinea pig everted ileum. The initial influxes of both dipeptides could be described by single Michaelis-Menten kinetics, having a nearly equal value of maximum influx. Mutual inhibition studies showed that the inhibition observed between Car and Gly-Gly was fully competitive, indicating that both Car and Gly-Gly share a common carrier. Although carrier-mediated influxes of the dipeptides were independent of Na+, the addition of the dipeptides into the mucosal solution evoked sudden and sustained increments of mucosal negativity. The changes in short-circuit current (delta Isc) evoked by the peptides increased as the Na+ concentration in the solution was increased, although both dipeptides evoked small increases in Isc, even in the absence of Na+. In spite of these common properties of transport and transport-related electrical phenomena, it was seen that the maximum change in transmural potential difference (delta PDt max) evoked by Car was about half that of Gly-Gly. Such a discrepancy between coincident Jmax values and values of delta PDt max suggests that the mechanism of induction of ionic flow is different for these two dipeptides.

Uptake of a series of neutral dipeptides including L-alanyl-L-alanine, glycylglycine and glycylsarcosine by hamster jejunum in vitro

This paper is the last of a set reporting an investigation of the kinetics of jejunal uptake and inhibitory ability of a series of neutral dipeptides, glycylglycine, L-ananyl-L-alanine, L-valyl-L-valine and L-leucyl-L-leucine, with progressively longer and more lipophilic side chains. The results suggested that at pH 5, uptake of L-alanyl-L-alanine, like that of L-valyl-L-valine and L-leucyl-L-leucine, was the result of two processes, uptake of intact peptide and uptake of free amino acid released extracellularly. On the other hand, uptake of glycylglycine was entirely in the form of intact peptide. In contrast to uptake of L-valyl-L-valine and L-leucyl-L-leucine, the proportion of intact L-alanyl-L-alanine taken up by mediated transport was greatest at the lowest concentration studied and smallest at the highest concentration. Taking the series of results as a whole, whereas the corresponding series of amino acids, glycine, L-alanine, L-valine and L-leucine, showed a progressive increase in apparent affinity for uptake and a decrease in Vmax, we could find no such regular progression with the peptides. The results of work on inhibition of uptake of one dipeptide by another were unexpectedly complex. Examples were the very powerful inhibitory effect of L-valyl-L-valine on uptake of glycylsarcosine, not suggested by the Kt of the former peptide, and the failure of glycylsarcosine to cause complete inhibition of uptake of L-alanyl-L-alanine and L-leucyl-L-leucine, though it could completely inhibit uptake of L-valyl-L-valine.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of glycylglycine and Na+ at the mucosal border of guinea-pig small intestine. A non-mutual stimulation of transport

Sodium-dependence of glycylglycine (Gly-Gly) influx and stimulation of Na+ transport by Gly-Gly were studied in everted sacs, sheet preparations and brush-border membrane vesicles isolated from guinea-pig ileum. Gly-Gly influx was found to be independent of the presence of Na+, while Na+ transport was stimulated by Gly-Gly as evidenced by increases in transmural potential difference (PDt), short-circuit current (Isc) and Na+ influx. The change in PDt (delta PDt) induced by Gly-Gly was a saturable function of Gly-Gly concentration, showing a Michaelis-Menten type relationship. The half-saturation concentration for Gly-Gly estimated from the electrical data was nearly identical with that estimated from influx data. At a constant Gly-Gly concentration the relationship between Isc and Na+ concentration was sigmoid, and the Hill coefficient was 1.5. Kinetic analysis according to Garay and Garrahan indicates that each Gly-Gly carrier has two equivalent non-interacting binding sites for Na+, and that translocation of Na+ occurs when the two Na+ sites on the carrier loaded with Gly-Gly are occupied by Na+. However, our results indicate that the resultant Na+ flow is not capable of stimulating Gly-Gly translocation.

Mechanisms of inhibition of glycylglycine transport by glycyl-L-leucine and L-leucine in guinea-pig small intestine

Inhibition of glycylglycine (Gly-Gly) transport by glycyl-L-leucine (Gly-Leu) and L-leucine was studied in isolated guinea-pig ileum. Kinetically, inhibition by Gly-Leu of Gly-Gly influx across the mucosal border was found to be mixed type, whereas the inhibition by leucine was "pseudo-competitive'. Kinetics of Gly-Leu inhibition, which could be defined as linear mixed type, suggests that Gly-Gly transport carrier has a high-affinity binding site for Gly-Leu besides the site for Gly-Gly, and that binding of Gly-Leu to its own site is inhibitory to Gly-Gly transport but independent of Gly-Leu transfer, Gly-Leu hydrolases at the brush border membrane had high-affinity component, but this did not seem to be related to the inhibitory binding of Gly-Leu, since bestatin (0.3 mM) completely suppressed the high-affinity component of the enzymes but little affected Gly-Gly transport. The "pseudo-competitive' type of inhibition by leucine suggests that the Gly-Gly carrier has another binding site to which leucine can bind, that leucine binding to this site is inhibitory to Gly-Gly transport and that leucine is partly transported by the Gly-Gly carrier system.

Characteristics of gamma-glutamyltranspeptidase in cultured skin fibroblasts from normals and cystinotics

The characteristics of a fluorimetric method for assay of gamma-glutamyltranspeptidase (EC 2.3.2.2) in cultured human skin fibroblasts from normal donors and cystinotic patients using gamma-glutamyl-7-amino-4-coumarin as substrate are described. It is possible with this method to measure enzymatic activity in sonicates of cells with as little as 0.029 mmol/l L-cystine as acceptor-substrate with only 0.20 mg of cellular protein after 30--60 min of incubation. The properties of the enzyme in cells from patients with cystine storage disease show elevated gamma-glutamyltranspeptidase under various incubation conditions.

Age-dependent change in intestinal absorption of dipeptides and their constituent amino acids in the guinea pig

The influxes from the mucosal solution to the enterocytes were investigated for glycylglycine, glycyl-L-leucine, and their constituent amino acids in isolated intestinal segments from suckling (3 to 4 days), weanling (10 to 14 days), and adult guinea pigs. Glycine and L-leucine influxes from the mucosal solution containing free glycine or L-leucine were not significantly different between sucklings and adults in either the jejunum or the ileum. On the other hand, glycylglycine and glycyl-L-leucine influxes were significantly greater in the following sequence: sucklings > weanlings > adults. Such age-dependent difference in dipeptide influx was more prominent in the jejunum than in the ileum. Kinetically, such developmental change in dipeptide influx was found to be related to the change in the value of Jmax (the maximum influx). The data indicated that the intact-peptide transfer mechanism has more important significance in protein hydrolysate absorption in immature stages of animals than in adults.