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PubMed1978

Isolation and identification of urinary beta-aspartyl dipeptides and their concentrations in human urine.

beta-Aspartyl-methionine, -aspartic acid and -glutamic acid and gamma-glutamyl-threonine and -glycine were isolated and identified in human urine by ion-exchange chromatography, high-voltage paper electrophoresis, acid hydrolysis and determination of N-terminal amino acids of the isolated compounds, and comparison of their behaviors in paper electrophoresis and chromatography with those of the authentic compounds. The concentrations of acidic beta-aspartyl dipeptides in human urine were determined using an amino acid analyzer. Their concentrations were as follows: beta-aspartyl-glycine, male, 44.4 +/- 8.5, female, 61.4 +/- 18.9, child, 83.7 +/- 27.1; -alanine, male, 11.0 +/- 4.9, female, 20.7 +/- 12.0, child, 25.3 +/- 9.1; -glutamic acid, male, 10.0 +/- 3.7, female, 23.0 +/- 8.5, child, 20.4 +/- 7.5; -serine, male, 9.9 +/- 2.8, female, 13.6 +/- 3.8, child, 14.9 +/- 4.7; -aspartic acid, male, 4.3 +/- 1.0, female, 9.1 +/- 2.2, child, 18.4 +/- 6.5; -threonine, male 3.9 +/- 0.9, female, 5.8 +/- 1.1, child, 13.2 +/- 4.9 mumol/g creatinine (mean +/- S.D.). The order of the sum of their concentrations tended to be child greater than female greater than male. Patients receiving intravenous hyperalimentation also excreted acidic beta-aspartyl dipeptides into urine in amounts similar to those in females and in a pattern similar to that observed in healthy persons. This finding indicates that urinary beta-aspartyl dipeptides were probably of endogenous origin because oral nutrition was stringently excluded in these patients.

Adolescent↗
PubMed1980

Ligand bindings of bovine carboxypeptidase B. III. Hydrophobic activators in dipeptide hydrolysis.

Several hydrophobic compounds acted as activators in dipeptide (Bz-Gly-L-Arg-OH, Z-Gly-L-Phe-OH) hydrolysis by bovine carboxypeptidase B. These hydrophobic compounds include Bz-Gly-OH, Z-Gly-OH, Z-L-Phe-OH, and Z-L-Phe-GLy-OH. These compounds were indicated to bind to the secondary substrate binding sites which is proposed to be responsible for substrate activation kinetics in dipeptide hydrolysis. Of the compounds Z-L-Phe-OH alone acted also as a inhibitor at higher concentrations, indicating that it binds to both primary and secondary sites as the dipeptide substrates do. Comparison of the activation effects of the compounds employed indicated that hydrophobic interaction played an important role in binding to the secondary site. Substrate and modifier binding constants were also determined and the results indicated that modifier binding increased both affinity and catalytic rate constant of the primary site. On the other hand, Z-Gly-OH and Z-L-Phe-Gly-OH inhibited the hydrolyses of tri and tetrapeptide substrates. This observation suggests that the secondary site is contained in the extended active center which the enzyme possibly has.

Alcohols↗
PubMed1990

Correlation between stability of a protein and its dipeptide composition: a novel approach for predicting in vivo stability of a protein from its primary sequence.

Statistical analysis of 12 unstable and 32 stable proteins revealed that there are certain dipeptides, the occurrence of which is significantly different in the unstable proteins compared with those in the stable ones. Based on the impact of these dipeptides on the unstable proteins over the stable ones, a weight value of instability is assigned to each of the dipeptides. For a given protein the summation of these weight values normalized to the length of its sequence helps to distinguish between unstable and stable proteins. Results suggest that the in vivo instability of proteins is possibly determined by the order of certain amino acids in its sequence. An attempt is made to correlate metabolic stability of proteins with features of their primary sequence where weight values of instability for a protein of known sequence could thus be used as an index for predicting its stability characteristics.

Amino Acid Sequence↗
PubMed1998

The utilization of dipeptides containing L-arginine by chicken macrophages.

L-Arginine is the precursor of NO, a cytotoxic agent of macrophages. Studies were carried out to determine whether dipeptides containing arginine can be utilized by lipopolysaccharide (LPS)-activated avian macrophages for NO production. A chicken macrophage cell line, the HD11 cell, was used in all experiments. Peptidase activities were observed in fetal bovine serum (FBS) and macrophage serum free medium (Mac-SFM). Therefore, the utilization of dipeptides by macrophages was examined using Dulbecco's modified Eagle medium (D-MEM), a chemically defined medium, in short-term culture without FBS. Nitrite accumulation in the culture medium was used as the indicator of NO production. At concentrations of 0.15 mM in the culture media, L-leucinyl-L-arginine was 89% as effective as L-arginine in providing substrate for NO production. L-Argininyl-L-leucine was 38% as effective as L-arginine. The effectiveness increased to 93 and 58%, respectively, when the concentrations of dipeptides and arginine were 1.0 mM. Both values were slightly higher in a second experiment (97 and 70%, respectively). L-Lysine (10 mM) inhibited nitrite formation from all three sources of L-arginine. In studies of initial rates of transport by HD11 cells in Hanks Balanced Salts solution (HBSS), both L-argininyl-L-leucine and L-leucinyl-L-arginine inhibited arginine uptake. As lysine and arginine share a common transporter for cationic amino acids and are known to compete for transport, these studies suggest that the peptides were hydrolyzed extracellularly, yielding arginine that was transported into the cell where it served as a substrate for NO synthesis.

Animals↗
PubMed1998

Glutamine dipeptides-supplemented parenteral nutrition reverses gut mucosal structure and interleukin-6 release of rat intestinal mononuclear cells after hemorrhagic shock.

Glutamine is an essential substrate for gut mucosal structure, but the role for gut immune function is not fully known. To determine the effect on gut cytokine release in relation to bacterial translocation and gut morphology, a nonlethal hemorrhagic shock (30 min, 30 mmHg) was performed in male Wistar rats followed by 4 days of different way of feeding. A conventional total parenteral nutrition (TPN) solution was compared with an isocaloric and isonitrogenous TPN solution supplemented with alanin-L-glutamine and glycyl-L-glutamine. An enteral chow-fed control group was included. Gut mononuclear cells and splenic macrophages were obtained and endotoxin-induced supernatant tumor necrosis factor-alpha (TNF) and interleukin-6 (IL-6) bioactivity was measured. Histological specimen of the small bowel were taken and mesenteric lymph nodes (MLN) were separated. Enteral feeding following hemorrhagic shock was accompanied by a normal mucosal structure and no bacterial translocation could be detected. TPN was characterized by suppression of cytokine release in gut mononuclear cells and splenic macrophages compared with the enteral-fed control (p < .05). Decreased TNF and IL-6 release was associated with a significantly increased mucosal injury score (p < .05) and a high incidence of bacterial translocation to MLN (66%, p < .05 vs. control). Supplementation of glutamine-dipeptides did not prevent TPN-induced bacterial translocation to MLN (p < .05 vs. control) but significantly improved mucosal injury (p < .05 vs. TPN). Down-regulation of TNF release in TPN-fed rats could not be reversed by glutamine dipeptides while IL-6 release was significantly increased compared with TPN-fed animals (p < .05), and no difference to enteral-fed controls could be found. Enteral nutrition following hemorrhagic shock is superior to parenteral nutrition with regard to mucosal structure, cytokine release, and bacterial translocation. Supplementation of TPN with glutamine dipeptides could reverse TPN-induced suppression of IL-6 release and improved mucosal structure, which may be beneficial in various disease conditions in which TPN is an integrated part of patients management.

Animals↗
PubMed1998

Antibacterial action of dipeptides containing an inhibitor of glucosamine-6-phosphate isomerase.

Several dipeptides, containing the N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid (FMDP) moiety linked to protein and non-protein amino acids, exhibited a strong growth-inhibitory and bactericidal effect against Bacillus subtilis. FMDP-dipeptides were efficiently transported into bacterial cells by a di-tripeptide permease and subsequently cleaved by intracellular Mn2+/Co2+-dependent peptidases. Cleavage rates [0.1-5.6 micromol min-1 (mg protein)-1] were about two orders of magnitude lower than transport rates [40-200 micromol min-1 (mg dry wt)-1]. The released FMDP inactivated glucosamine-6-phosphate (GlcN-6-P) isomerase, an enzyme catalysing the first committed step in a biosynthetic pathway leading to amino sugar-nucleotide precursors of bacterial peptidoglycan. Inhibition of GlcN-6-P isomerase precluded peptidoglycan biosynthesis and resulted in a strong bacteriolytic effect. Results of the studies on consequences of GlcN-6-P isomerase inhibition upon the action of FMDP-dipeptides provided evidence demonstrating that the lack of endogenous GlcN-6-P could be a reason for the triggering of bacterial autolysis. Peptides containing the inhibitors of GlcN-6-P isomerase are one of the very few antimicrobial agents known that exhibit both bactericidal and fungicidal effects.

Aldose-Ketose Isomerases↗
PubMed2006

Molecular interactions between dipeptides, drugs and the human intestinal H+ -oligopeptide cotransporter hPEPT1.

The human intestinal proton-coupled oligopeptide transporter hPEPT1 has been implicated in the absorption of pharmacologically active compounds. We have investigated the interactions between a comprehensive selection of drugs, and wild-type and variant hPEPT1s expressed in Xenopus oocytes, using radiotracer uptake and electrophysiological methods. The beta-lactam antibiotics ampicillin, amoxicillin, cephalexin and cefadroxil, the antineoplastics delta-aminolevulinic acid (delta-ALA) and bestatin, and the neuropeptide N-acetyl-Asp-Glu (NAAG), were transported, as judged by their ability to evoke inward currents. When the drugs were added in the presence of the typical substrate glycylsarcosine (Gly-Sar), the inward currents were equal or less than that induced by Gly-Sar alone. This suggests that the drugs are transported at a lower turnover rate than Gly-Sar, but may also point towards complex interactions between dipeptides, drugs and the transporter. Gly-Sar and the drugs also modified the kinetics of hPEPT1 presteady-state charge movement, by causing a reduction in maximum charge (Qmax) and a shift of the midpoint voltage (V0.5) to more negative potentials. Our results indicate that the substrate selectivity of hPEPT1 is: Gly-Sar > NAAG, delta-ALA, bestatin > cefadroxil, cephalexin > ampicillin, amoxicillin. Based on steady-state and presteady-state analysis of Gly-Sar and cefadroxil transport, we proposed an extension of the 6-state kinetic model for hPEPT1 function that globally accounts for the observed presteady-state and steady-state kinetics of neutral dipeptide and drug transport. Our model suggests that, under saturating conditions, the rate-limiting step of the hPEPT1 transport cycle is the reorientation of the empty carrier within the membrane. Variations in rates of drug cotransport are predicted to be due to differences in affinity and turnover rate. Oral availability of drugs may be reduced in the presence of physiological concentrations of dietary dipeptides in the gut, suggesting that oral delivery drugs should be taken on an empty stomach. The common hPEPT1 single-nucleotide polymorphisms Ser117Asn and Gly419Ala retained the essential kinetic and drug recognition characteristics of the wild type, suggesting that neither variant is likely to have a major impact on oral absorption of drugs.

Animals↗
PubMed2003

Interactions of the dipeptide ester prodrugs of acyclovir with the intestinal oligopeptide transporter: competitive inhibition of glycylsarcosine transport in human intestinal cell line-Caco-2.

The oligopeptide transporter may be exploited to enhance the absorption of drugs by synthesizing their dipeptide ester prodrugs, which may be recognized as its substrates. Various dipeptide esters of acyclovir (ACV), an antiviral nucleoside analog, were synthesized. Enzymatic hydrolysis and affinity of the prodrugs toward the human intestinal peptide transporter hPEPT1 were studied using the human intestinal Caco-2 cell line. Affinity studies were performed by inhibiting the uptake of [(3)H]glycylsarcosine by the prodrugs. The uptake of glycylsarcosine was found to be saturable at higher concentrations and was competitively inhibited by the prodrugs of ACV. All prodrugs except Tyr-Gly-ACV demonstrated a higher affinity (1.41-4.96 mM) toward hPEPT1 than cephalexin (8.19 +/- 2.12 mM), which was used as a positive control. Two prodrugs, Gly-Val-ACV and Val-Val-ACV, showed comparable affinity to Val-ACV, an amino acid prodrug of ACV recognized by PEPT1/PEPT2. The permeability of Gly-Val-ACV (2.99 +/- 0.59 x 10(-6) cm/s) across Caco-2 was comparable with that of Val-ACV (3.01 +/- 0.21 x 10(-6) cm/s) and was significantly inhibited (63%) in presence of glycylsarcosine. The transport of GVACV across Caco-2 was saturable at higher concentrations, and the parameters were calculated as K(m) 3.16 +/- 0.31 mM and V(max) 0.014 +/- 0.00058 nmol cm(-2) min(-1). Overall, the results suggest that the dipeptide prodrugs of ACV have a high affinity toward the intestinal oligopeptide transporter hPEPT1 and therefore seem to be promising candidates in the treatment of ocular and oral herpesvirus infections, because cornea and intestinal epithelia seem to express the oligopeptide transporters.

Acyclovir↗
PubMed2003

Effects of organic anion, organic cation, and dipeptide transport inhibitors on cefdinir in the isolated perfused rat kidney.

Cefdinir (Omnicef; Abbott Laboratories) is a cephalosporin antibiotic primarily eliminated by the kidney. Nonlinear renal elimination of cefdinir has been previously reported. Cefdinir renal transport mechanisms were studied in the erythrocyte-free isolated perfused rat kidney. Studies were performed with drug-free perfusate and perfusate containing cefdinir alone to establish the baseline physiology and investigate cefdinir renal elimination characteristics. To investigate cefdinir renal transport mechanisms, inhibition studies were conducted by coperfusing cefdinir with inhibitors of the renal organic anion (probenecid), organic cation (tetraethylammonium), or dipeptide (glycylsarcosine) transport system. Cefdinir concentrations in biological samples were determined using reversed-phase high-performance liquid chromatography. Differences between treatments and controls were evaluated using analysis of variance and Dunnett's test. The excretion ratio (ER; the renal clearance corrected for the fraction unbound and glomerular filtration rate) for cefdinir was 5.94, a value indicating net renal tubular secretion. Anionic, cationic, and dipeptide transport inhibitors all significantly affected the cefdinir ER. With probenecid, the ER was reduced to 0.59, clearly demonstrating a significant reabsorptive component to cefdinir renal disposition. This finding was confirmed by glycylsarcosine studies, in which the ER was elevated to 7.95, indicating that reabsorption was mediated, at least in part, by the dipeptide transporter system. The effects of the organic cation tetraethylammonium, in which the ER was elevated to 7.53, were likely secondary in nature. The anionic secretory pathway was found to be the predominant mechanism for cefdinir renal excretion.

Animals↗
PubMed1989

Mechanism and energetics of dipeptide transport in membrane vesicles of Lactococcus lactis.

Alanyl-alpha-glutamate transport has been studied in Lactococcus lactis ML3 cells and in membrane vesicles fused with liposomes containing beefheart cytochrome c oxidase as a proton-motive-force-generating system. The uptake of Ala-Glu observed in de-energized cells can be stimulated 26-fold upon addition of lactose. No intracellular dipeptide pool could be detected in intact cells. In fused membranes, a 40-fold accumulation of Ala-Glu was observed in response to a proton motive force. Addition of ionophores and uncouplers resulted in a rapid efflux of the accumulated dipeptide, indicating that Ala-Glu accumulation is directly coupled to the proton motive force as a driving force. Ala-Glu uptake is an electrogenic process and the dipeptide is transported in symport with two protons. In both fused membranes and intact cells the same affinity constant (0.70 mM) for Ala-Glu uptake was found. Accumulated Ala-Glu is exchangeable with externally added alanyl-glutamate, glutamyl-glutamate, and leucyl-leucine, while no exchange occurred upon addition of the amino acid glutamate or alanine. These results indicate that the Ala-Glu transport system has a broad substrate specificity.

Amino Acids↗
PubMed1995

Medium-dependent regulation of proteinase gene expression in Lactococcus lactis: control of transcription initiation by specific dipeptides.

Transcriptional gene fusions with the Escherichia coli beta-glucuronidase gene (gusA) were used to study the medium- and growth-dependent expression of the divergently transcribed genes involved in proteinase production (prtP and prtM) of Lactococcus lactis SK11. The results show that both the prtP and prtM genes are controlled at the transcriptional level by the peptide content of the medium and, to a lesser extent, by the growth rate. A more than 10-fold regulation in beta-glucuronidase activity was observed for both prtP and prtM promoters in batch and continuous cultures. The level of expression of the prtP and prtM promoters was high in whey permeate medium with relatively low concentrations of peptides, whereas at increased concentrations the expression of the promoters was repressed. The lowest level of expression was observed in peptide- and amino acid-rich laboratory media, such as glucose-M17 and MRS. The addition of specific dipeptides, such as leucylproline and prolylleucine, to the growth medium negatively affected the expression of the prtP-gusA fusions. The repression by dipeptides was not observed in mutants defective in the uptake of di-tripeptides, indicating that the internal concentration of dipeptides or derivatives is important in the regulation of proteinase production.

Bacterial Proteins↗
PubMed2001

Effect of sequences of the active-site dipeptides of DsbA and DsbC on in vivo folding of multidisulfide proteins in Escherichia coli.

We have examined the role of the active-site CXXC central dipeptides of DsbA and DsbC in disulfide bond formation and isomerization in the Escherichia coli periplasm. DsbA active-site mutants with a wide range of redox potentials were expressed either from the trc promoter on a multicopy plasmid or from the endogenous dsbA promoter by integration of the respective alleles into the bacterial chromosome. The dsbA alleles gave significant differences in the yield of active murine urokinase, a protein containing 12 disulfides, including some that significantly enhanced urokinase expression over that allowed by wild-type DsbA. No direct correlation between the in vitro redox potential of dsbA variants and the urokinase yield was observed. These results suggest that the active-site CXXC motif of DsbA can play an important role in determining the folding of multidisulfide proteins, in a way that is independent from DsbA's redox potential. However, under aerobic conditions, there was no significant difference among the DsbA mutants with respect to phenotypes depending on the oxidation of proteins with few disulfide bonds. The effect of active-site mutations in the CXXC motif of DsbC on disulfide isomerization in vivo was also examined. A library of DsbC expression plasmids with the active-site dipeptide randomized was screened for mutants that have increased disulfide isomerization activity. A number of DsbC mutants that showed enhanced expression of a variant of human tissue plasminogen activator as well as mouse urokinase were obtained. These DsbC mutants overwhelmingly contained an aromatic residue at the C-terminal position of the dipeptide, whereas the N-terminal residue was more diverse. Collectively, these data indicate that the active sites of the soluble thiol- disulfide oxidoreductases can be modulated to enhance disulfide isomerization and protein folding in the bacterial periplasmic space.

Catalytic Domain↗
PubMed1973

The effect of amino acids and dipeptides on sodium and water absorption in man.

A perfusion technique has been used to quantitate the effect of the amino acids glycine and alanine and the dipeptides glycyl-glycine and glycyl-L-alanine on sodium and water absorption from the human jejunum. Although no net absorption of sodium and water was seen in the absence of non-electrolytes, a significant stimulation occurred in the presence of both free amino acids and dipeptides. In the case of glycine and alanine, sodium and water absorption increased linearly with increasing concentration of the amino acid and saturation was not demonstrated over the range of concentrations studied. Molar ratios for net absorption of free amino acid and sodium were approximately 1:1 for all but the highest concentration of alanine. In contrast, the corresponding molar ratios for the two dipeptide solutions and sodium were approximately 1:2. Possible explanations for these observations are discussed.

Adult↗
PubMed1980

The transport of dipeptides by the small intestine.

During steady-state transfer across the vascularly perfused anuran small intestine, the intracellular concentration of L-leucine never exceeded its concentration in the lumen. However, during periods of stopped vascular flow accumulation did occur and this was dependent upon the presence of sodium in the luminal solution. Similar observations were made for leucine from the dipeptides L-leucylglycine and glycyl-L-leucine, although the intracellular accumulation of leucine from these peptides in the presence of sodium was considerably lower than from the free amino acid. In contrast, the dipeptide L-carnosine (beta-alanyl-L-histidine) was not accumulated by the tissue in the presence or absence of luminal sodium. Also, the uptake of this poorly hydrolyzed peptide by tissue rings was unaffected either by sodium substitution or by the presence of L-leucylglycine, glycyl-L-leucine, or glycyl-L-proline. Only free L-leucine was found to inhibit the peptide's uptake significantly. It was concluded that there are two routes of uptake for amino acids from dipeptides. One is shared with free amino acids and is sodium dependent and concentrative. The other "peptide route" is nonconcentrative and not influenced by luminal sodium. Carnosine appears to be taken up by a second, apparently sodium-independent route.

Animals↗
PubMed1996

Basolateral dipeptide transport by the intestine of the teleost Oreochromis mossambicus.

Transport characteristics of [14C]glycylsarcosine ([14C]Gly-Sar) were measured in herbivorous tilapi (Oreochromis mossambicus) intestinal basolateral membrane vesicles (BLMV) purified with Percoll gradient centrifugation. Specific activity of the vesicle Na(+)-K(+)-adenosinetriphos- phatase was increased 12-fold, whereas specific activity of the brush-border enzyme alkaline phosphatase was enriched only by 0.8-fold. [14C]Gly-Sar uptake was stimulated by increasing concentrations of extravesicular protons rather than by a transmembrane proton gradient. A transmembrane K+ diffusion potential (inside negative) did not stimulate [14C]Gly-Sar uptake above that observed with short-circuited vesicles. An inwardly directed Na+ gradient had no effect on peptide uptake. Kinetic analysis of basolateral transport rate revealed that the transport occurred by a saturable process conforming to Michaelis-Menten kinetics [Kt [concentration of [14C]Gly-Sar that yielded one-half of maximal influx (Jmax)] = 13.27 +/- 3.80 mM, Jmax = 15,155 +/- 3,096 pmol.mg protein-1.6 s-1]. The basolateral transporter was insensitive to diethylpyrocarbonate (DEP), a specific inhibitor of proton-coupled peptide transport systems. [14C]Gly-Sar influx into tilapia BLMV showed cis-inhibition by several other dipeptides, suggesting that the [14C]Gly-Sar transporter was shared by other peptides too. These observations strongly suggest that the basolateral intestinal dipeptide transporter in herbivorous fishes is distinctly different from either the high- or low-affinity brush-border transporter. It is proton dependent, electroneutral, sodium independent and accepts a wide variety of dipeptides.

Animals↗
PubMed1988

Evidence for active dipeptide transport in isolated proximal straight tubules.

Transport of the dipeptide glycylsarcosine (Gly-Sar) was examined in isolated proximal straight tubules of the rabbit kidney by an in vitro microperfusion technique to determine whether it can be actively transported intact. The unidirectional lumen-to-bath flux of Gly-Sar was measured by two separate methods, namely its appearance rate (JA) in the bathing fluid and its disappearance rate (JD) from the luminal fluid. In addition, the cell Gly-Sar concentration was measured immediately after the last flux period. Mean luminal fluid Gly-Sar concentration was 0.22 mM. Transepithelial Gly-Sar flux (260.0 fmol.min-1.mm-1) was greater than could be accounted for by passive leakage, whereas cellular Gly-Sar accumulation (2.72 mM) was greater than could be attributed to passive equilibration across the luminal membrane. High-pressure liquid chromatographic analysis of cellular extract indicated that 63% of the transported Gly-Sar was hydrolyzed within the cell. Analysis of the bath solution revealed that 47% of the radioactivity that crossed the tubule cell was in the form of intact dipeptide, whereas the remainder of the radioactivity was in the form of hydrolytic and metabolic products of Gly-Sar. This indicates that the dipeptide Gly-Sar is actively transported intact at the luminal membrane into the cytosol of proximal straight tubule cells with subsequent hydrolysis. It then exits across the basolateral membrane as intact Gly-Sar and its hydrolytic and metabolic products.

Algorithms↗
PubMed1991

Multiple carriers for dipeptide transport: carrier-mediated transport of glycyl-L-proline in renal BBMV.

To determine whether multiple carriers are responsible for luminal uptake of glycyl-L-proline (Gly-Pro) in the renal proximal tubule, transport of Gly-[3H]Pro was measured in brush-border membrane vesicles (BBMV). A Line-weaver-Burk analysis of Michaelis-Menten kinetics revealed the presence of two carriers: a lower affinity, higher capacity carrier (Km = 1.3 x 10(-2) M; Vmax = 4.6 x 10(-8) mol.mg-1.min-1) and a higher affinity, lower capacity carrier (Km = 2.7 x 10(-7) M; Vmax = 7.8 x 10(-13) mol.mg-1.min-1). The dipeptides Gly-Sar, beta Ala-His, and pyroGlu-His competitively inhibited the low-affinity carrier. No effect on the Km or Vmax of Gly-Pro transport in this range was seen in the presence of the dipeptides Gly-Gly or cycloHis-Pro. The high-affinity carrier exhibited a different inhibition spectrum. Competitive inhibition of Gly-Pro transport was demonstrated for the dipeptides Gly-Gly and Gly-Sar. However, none of the other peptides tested above altered Gly-Pro transport in the high-affinity range, including pyroGlu-His, which is transported by a high-affinity carrier. At both low (4 x 10(-8) M) and high (4 x 10(-3) M) concentrations, uptake of Gly-Pro was stimulated in the presence of an inwardly directed H+ gradient but was unaffected by the presence of an inward Na+ gradient. In addition, measurements in the presence of valinomycin and an outwardly directed K+ gradient strongly suggest that H(+)-stimulated uptake at both concentrations is electrogenic.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1981

Effect of amino acids and dipeptides on ethanol absorption across the rat intestine.

Effects of amino acids and dipeptides on ethanol (50 mM) absorption were studied by in vivo perfusion of the rat intestine. All the amino acids and dipeptides tested enhanced the rate of ethanol absorption over that observed with a control solution containing an equimolar concentration of mannitol. The increase in the rate of ethanol absorption can be related to the entry of ethanol with water which accompanies the active absorption of these nutrients. Some amino acids and dipeptides like lysine, tryptophan and glycyl-phenylalanine have an additional stimulatory effect on ethanol absorption which seems unrelated to water movement.

Amino Acids↗