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T Katada

Publications and source records attributed to T Katada.

At least 55 records · Page 3Linked to original sources
PubMed1997

Conformation-dependent activation of type II adenylyl cyclase by protein kinase C.

Phorbol ester treatment enhanced the catalytic activity of type II adenylyl cyclase overexpressed in insect cells. In cells coexpressing type II adenylyl cyclase and protein kinase C-alpha, type II adenylyl cyclase catalytic activity was higher even in the absence of phorbol ester treatment; phorbol ester treatment further and markedly enhanced type II adenylyl cyclase catalytic activity. However, this enhancement, either by phorbol ester treatment or by coexpression of protein kinase C-alpha, was lost following membrane solubilization with detergents. This attenuation was unaffected by phosphatase inhibitor or salts. In contrast, membrane solubilization did not affect forskolin-stimulated type II adenylyl cyclase catalytic activity. Purified type II adenylyl cyclase was stimulated by forskolin and Gs alpha, but not by protein kinase C-alpha. Therefore, a specific mammalian protein kinase C isoenzyme can activate type II adenylyl cyclase, but the mechanism clearly differs from that underlying either Gs alpha- or forskolin-mediated stimulation.

Adenylyl Cyclases↗
PubMed1997

Cyclic ADP-ribose measurements in rat pancreatic islets.

Cyclic ADP-ribose was measured by a radioimmunological procedure in rat pancreatic islets. The cyclic ADP-ribose content of the islets was much lower immediately after isolation (< or = 2.3 +/- 0.2 fmol/islet) than after a further incubation of 90 min in a salt-balanced medium (26.4 +/- 1.3 fmol/islet). Under the latter condition, the islet cyclic ADP-ribose content was not affected by the concentration of D-glucose and/or D-fructose in the incubation medium and, when expressed per micrograms protein, was 3- to 30-fold higher than that found in other biological samples such as liver, whole pancrease or tumoral islet cells. Although these findings might suggest a physiological role for cyclic ADP-ribose in islet cells, they argue against the view that the cyclic nucleotide acts as a coupling factor in the process of hexosestimulated insulin release.

Adenosine Diphosphate Ribose↗
PubMed1997

Identification, sequence, and expression of an invertebrate caveolin gene family from the nematode Caenorhabditis elegans. Implications for the molecular evolution of mammalian caveolin genes.

Caveolae are vesicular organelles that represent an appendage of the plasma membrane. Caveolin, a 21-24-kDa integral membrane protein, is a principal component of caveolae membranes in vivo. Caveolin has been proposed to function as a plasma membrane scaffolding protein to organize and concentrate signaling molecules within caveolae, including heterotrimeric G proteins (alpha and betagamma subunits). In this regard, caveolin interacts directly with Galpha subunits and can functionally regulate their activity. To date, three cDNAs encoding four subtypes of caveolin have been described in vertebrates. However, evidence for the existence of caveolin proteins in less complex organisms has been lacking. Here, we report the identification, cDNA sequence and genomic organization of the first invertebrate caveolin gene, Cavce (for caveolin from Caenorhabditis elegans). The Cavce gene, located on chromosome IV, consists of two exons interrupted by a 125-nucleotide intron sequence. The region of Cavce that is strictly homologous to mammalian caveolins is encoded by a single exon in Cavce. This suggests that mammalian caveolins may have evolved from the second exon of Cavce. Cavce is roughly equally related to all three known mammalian caveolins and, thus, could represent a common ancestor. Remarkably, the invertebrate Cavce protein behaves like mammalian caveolins: (i) Cavce forms a high molecular mass oligomer, (ii) assumes a cytoplasmic membrane orientation, and (iii) interacts with G proteins. A 20-residue peptide encoding the predicted G protein binding region of Cavce possesses "GDP dissociation inhibitor-like activity" with the same potency as described earlier for mammalian caveolin-1. Thus, caveolin appears to be structurally and functionally conserved from worms to man. In addition, we find that there are at least two caveolin-related genes expressed in C. elegans, defining an invertebrate caveolin gene family. These results establish the nematode C. elegans as an invertebrate model system to study caveolae and caveolin in vivo.

Amino Acid Sequence↗
PubMed1997

Mapping of the catalytic and epitopic sites of human CD38/NAD+ glycohydrolase to a functional domain in the carboxyl terminus.

We reported that 1) ecto-NAD+ glycohydrolase (NADase) activity induced upon differentiation of HL-60 cells is localized on the extracellular carboxyl-terminal side of CD38 and that 2) CD38 ligation by specific mAbs is followed by protein tyrosine phosphorylation in the cells. The strategy selected for identifying the relevant catalytic domains of the molecule relies upon the production in COS-7 cells of carboxyl-terminal deletion mutants of CD38. The mutants with fewer than 15 amino acids deleted at the carboxyl terminus of the 300-amino acid wild-type molecule maintained NADase activity, whereas those with more than 27 amino acids deleted did not. The general inference is that the carboxyl-terminal 273-285 sequence bears the site of enzyme activity. Introduction of site-directed mutation of a conserved cysteine residue (Cys275), located in the 273-285 sequence, completely abolished NADase activity. The second issue resolved in this work is the definition of an epitope of the agonistic anti-CD38 mAbs. To this aim, a panel of selected anti-CD38 mAbs was tested using these mutants and various CD38 fragments as the target in immunoblot analyses. All of the epitopes recognized by mAbs inducing protein tyrosine phosphorylation were mapped on an identical site containing the carboxyl-terminal sequence of 273-285. The conclusion is that the discrete carboxyl-terminal sequence identified in the present study not only plays a key role in its ecto-NADase activity, but actually constitutes the epitopes exploited by the agonistic anti-CD38 mAbs for transmembrane signaling.

ADP-ribosyl Cyclase↗
PubMed1997

Molecular characterization of rat T lymphocyte alloantigen RT6.1 as an ADP-ribosyltransferase.

A family of glycosylphosphatidylinositol-linked ADP-ribosyltransferases, of which cDNAs were cloned from various mammalian cells, possess a common Glu-rich motif (EEEVLIP) near their carboxyl termini. Although the first Glu in the common motif is replaced by Gln (Q207EEVLIP) in rat T lymphocyte alloantigens RT6.1 and RT6.2, the two RT6s appear to have ADP-ribosyltransferase activity. To investigate the significance of the Glu-rich motif in the enzyme activity, we produced a mutant RT6.1, in which Gln207 was replaced by Glu (Q207E), together with wild-type RT6s, in Escherichia coli. The recombinant RT6.1 and RT6.2 displayed extremely low auto-ADP-ribosylation, though the latter modification was somewhat higher than the former one. In contrast, much higher the auto-modification was observed for Q207E mutant. Moreover, the mutant could effectively ADP-ribosylate agmatine as a substrate. Thus, the single amino acid mutation of RT6.1 caused remarkable increase in its ADP-ribosyltransferase activity, indicating that the Glu-rich motif near the carboxy terminus plays an important role in the enzyme activity.

ADP Ribose Transferases↗
PubMed1997

Signal transduction via the CD38/NAD+ glycohydrolase.

The human cell surface CD38 molecule is a 46-kDa type-II transmembrane glycoprotein with a short N-terminal cytoplasmic domain and a long Cys-rich C-terminal extracellular one. We previously demonstrated that an ecto-form NAD+ glycohydrolase (NADase) activity induced by all-trans retinoic acid in HL-60 cells is due to the extracellular domain of CD38. In the present study, we investigated a possible signal transduction mediated through CD38 in the retinoic acid-differentiated HL-60 cells with anti-CD38 monoclonal antibodies (mAbs). The addition of selected anti-CD38 mAbs to the cells induced rapid tyrosine phosphorylation of the cellular proteins with the molecular weights of 120,000, 87,000 and 77,000; the phosphorylated 120-kDa protein was identified as the c-cbl proto-oncogene product, p120c-cbl. Furthermore, the phosphorylated p 120c-cbl associated with the 85-kDa subunit of phosphatidylinositol 3-kinase. To determine the relationship between the amino acid sequence responsible for the NADase activity and epitopes recognized by the stimulatory mAbs, we produced its carboxy-terminal deletion mutants in COS-7 cells. The mutants with less than 15 amino acids deleted from the carboxyl terminus of the 300-amino acid wild-type molecule still maintained NADase activity, but those with more than 27 amino acids deleted did not. Introduction of site-directed mutation of a cysteine residue (Cys275), located in the 273-285 sequence, completely abolished the NADase activity. These CD38 mutants were also used for an epitope mapping of anti-CD38 mAbs. All the epitopes recognized by the mAbs inducing the tyrosine phosphorylation were mapped on the same Cys275-containing sequence of 273-285. Thus, the discrete carboxy-terminal sequence not only plays a key role in its ecto-NADase activity, but also contains the epitopes of the agonistic anti-CD38 mAbs for the transmembrane signaling. We also found that the agonistic mAbs markedly potentiate superoxide generation induced by the stimulation of G protein-coupled chemotactic receptors. Our results suggested that the stimulation of CD38 might generate an accessory signal(s) to enhance the G protein-mediated signaling, probably though the protein-tyrosine phosphorylation.

ADP-ribosyl Cyclase↗
PubMed1997

Immunosuppression by ultraviolet B rays via eyes in mice.

Irradiation by ultraviolet B (UV-B; 280-320 nm) initiates suppression of contact hypersensitivity. Immunosuppression was induced in C57BL/6N Crj mice by exposure of the dorsal skin or the eyes to a 10 kJ/m2 dose of UV-B radiation from 20SE sunlamps, followed by sensitization with 0.5% fluorescein isothiocyanate (FITC). The degree of immunosuppression induced by UV-B eye irradiation was equal to that induced by UV-B skin irradiation. When mice were irradiated with UV-B into the eyes after the optic nerve had been cut, systemic immunosuppression was not induced.

Animals↗
PubMed1997

Potentiation of chemotactic peptide-induced superoxide generation by CD38 ligation in human myeloid cell lines.

CD38 is a type II transmembrane glycoprotein possessing an NAD+ glycohydrolase activity in its extracellular domain. We previously reported that the ligation of CD38 by a monoclonal antibody (mAb), HB-7, induces the tyrosine phosphorylation of cellular proteins including p120(c-cbl) in differentiated human myeloid cell lines and that the phosphorylated p120(c-cbl) is capable of binding to phosphatidylinositol (PI) 3-kinase. In the present study, we found that the agonistic anti-CD38 mAb markedly potentiates superoxide generation stimulated by chemotactic formyl-Met-Leu-Phe receptors in the CD38-producing cells. HB-7 neither generated superoxide by itself nor enhanced the cell response induced by phorbol 12-myristate acetate, indicating that the potentiating action of the anti-CD38 mAb is specific for the stimulation by the GTP-binding protein (G1)-coupled membrane receptors. The potentiation by HB-7 was abolished by prior treatment of the cells with a tyrosine kinase inhibitor, pertussis toxin, or a potent PI 3-kinase inhibitor, wortmannin. HB-7 also enhanced the product formation of PI 3-kinase in response to the chemotactic receptor stimulation, without significant changes in the receptor-stimulated accumulations of inositol-1,4,5-trisphosphate, arachidonate release, and intracellular Ca2+. These results indicate that the CD38-induced tyrosine phosphorylation has a cross-talk with the chemotactic receptor/G1-mediated signal transduction pathway resulting in the enhancement of superoxide generation, probably through the activation of PI 3-kinase.

ADP-ribosyl Cyclase↗
PubMed1997

Characterization of sphingosine 1-phosphate-induced actions and its signaling pathways in rat hepatocytes.

Sphingosine 1-phosphate (S-1-P) and lysophosphatidic acid (LPA) stimulated glycogen phosphorylase, a rate-limiting enzyme responsible for glycogenolysis, in association with Ca2+ mobilization and phospholipase C (PLC) activation in rat hepatocytes. S-1-P, but not LPA, also inhibited adenosine 3',5'-cyclic monophosphate accumulation reflecting adenylyl cyclase inhibition. S-1-P-induced PLC activation, Ca2+ mobilization, and phosphorylase activation were markedly enhanced by primary culture of the cells for 24 h, whereas the inhibitory adenosine 3',5'-cyclic monophosphate response was unchanged by increasing culture time. Activation of the PLC-Ca2+ system during primary culture was specific to the lysosphingolipid; PLC and Ca2+ responses to LPA and NaF were unchanged or slightly attenuated by increasing culture time. Pertussis toxin treatment almost completely suppressed the S-1-P-induced inhibition of adenylyl cyclase but hardly influenced the lipid-induced activation of PLC and its cascade reactions. We conclude that S-1-P, through an LPA receptor-independent mechanism, stimulates two signaling pathways, i.e., activation of the PLC-Ca2+ system and inhibition of adenylyl cyclase, through distinct S-1-P receptor-transducer systems, resulting in the modulation of glycogenolysis in rat hepatocytes.

Animals↗
PubMed1997

[The aggressivity in schizophrenics].

Three young male patients with schizophrenia who developed aggressive acts towards themselves and others, suicide attempts, assaults, and a murder, are reported and discussed from the viewpoints of the language and the symbolization. The characteristics reported in proceeding researches were found in these three schizophrenics. It was when these patients interrogated, "What is the father?" that the psychosis was triggered and that the aggressivity closely connected with the conception of the death became manifest. These patients interrogated themselves as to being human and had to prove that they belonged to the human beings. Why the aggressivity in schizophrenics becomes manifest in this way? Because the symbolization didn't take place in schizophrenics and they were not subject to the internal death, necessary to be structured in the symbolic dimension. As a result, when they are asked, "What is the father? What is the human?" at the beginning of the psychosis, the manifests without symbolic articulation. The aggressivity in schizophrenics is considered as the function to murder the and to induce the internal death from the outside. It's Law-of-the-Father that inhibits the manifestation of the for subjects in the symbolic dimension. However, Law-of-the-Father doesn't function in schizophrenics and returns in the delusion and the hallucination at the beginning of the psychosis when 'what is the father' comes in question. The absolute other exhibiting Law-of-the-Father orders the murder of the , and in consequence the aggressivity manifests by the orders.

Adult↗
PubMed1996

Association of phosphatidylinositol 3-kinase with the proto-oncogene product Cbl upon CD38 ligation by a specific monoclonal antibody in THP-1 cells.

We reported that ecto-NAD+ glycohydrolase activity induced upon differentiation of HL-60 cells with retinoic acid is localized on the extracellular domain of CD38 and that CD38 ligation by a specific monoclonal antibody, HB-7, is followed by rapid tyrosine phosphorylation of cellular proteins including a proto-oncogene product, Cbl. In the present study, we investigated intracellular signaling linked to the HB-7-induced Cbl phosphorylation in dibutyryl cAMP-treated THP-1 cells. The 85-kDa regulatory subunit (p85) of phosphatidylinositol (PI) 3-kinase was immunoprecipitated with anti-Cbl antibody in a manner dependent on the tyrosine phosphorylation of Cbl. PI 3-kinase activity was also observed in the immunoprecipitated fractions containing tyrosine-phosphorylated Cbl. The phosphorylated form of Cbl, which had been separated from the CD38-stimulated cells, was capable of directly binding to a recombinant p85 fused to glutathione S-transferase. Thus, the direct association of tyrosine-phosphorylated Cbl with PI 3-kinase, possibly leading to the kinase activation, appeared to be involved in intracellular signaling caused by the CD38 ligation.

ADP-ribosyl Cyclase↗
PubMed1996

Involvement of the beta gamma subunits of inhibitory GTP-binding protein in chemoattractant receptor-mediated potentiation of cyclic AMP formation in guinea pig neutrophils.

Cellular cyclic AMP formation in response to prostaglandin (PG) E1 was markedly potentiated by the chemoattractant formyl-Met-Leu-Phe (fMLP) in guinea pig neutrophils. This potentiation by fMLP was abolished by prior treatment of the cells with pertussis toxin, but not by the prevention of an fMLP-induced intracellular Ca2+ increase in the cells, indicating the direct involvement of the inhibitory GTP-binding protein (Gj), but not Ca2+, in the fMLP-induced potentiation of cyclic AMP formation. Cyclic AMP formation in the neutrophils was also unique in response to forskolin; the diterpene inhibited cyclic AMP formation stimulated by PGE1 plus fMLP at low concentrations, but it slightly stimulated the basal and fMLP-induced cyclic AMP formation at high concentrations. Such a forskolin-induced inhibition was also observed in the adenylyl cyclase of the cell membranes and detergent extract therefrom only when the cyclase was activated by GTP or its nonhydrolyzable analogue (GTP gamma S). The forskolin-inhibitable activity could be affinity-purified from the GTP gamma S-treated cell membranes with a forskolin-agarose column. The cyclase appeared to be purified as a complex with the GTP gamma S-bound alpha subunit of the stimulatory GTP-binding protein (Gs alpha), but not with the beta gamma subunits, as judged from immunoblot analysis with specific antisera. The GTP gamma S-bound Gs alpha-stimulated cyclase activity was further enhanced by beta gamma, and this enhancement was again inhibited by forskolin. These results suggest that the GTP-bound Gs alpha produced by PGE1 receptor stimulation and the beta gamma subunits released from Gj by fMLP receptor stimulation were acting synergistically in the cyclic AMP formation of intact neutrophils.

Adenylyl Cyclases↗
PubMed1996

Intrinsic signaling function of APP as a novel target of three V642 mutations linked to familial Alzheimer's disease.

APP695 is a transmembrane precursor of Abeta amyloid. In familial Alzheimer's disease (FAD), three mutations V642I/F/G were discovered in APP695, which has been suggested by multiple studies to be a cell surface signaling receptor. We previously reported that normal APP695 encodes a potential GO-linked receptor with ligand-regulated function and that expression of the three FAD mutants (FAD-APPs), not normal APP, induces cellular outputs by GO-dependent mechanisms. This suggests that FAD-APPs are constitutively active GO-linked receptors. Here, we provide direct evidence for this notion. Reconstitution of either recombinant FAD-APP with GO vesicles induced activation of GO, which was inhibitable by pertussis toxin, sensitive to Mg2+ and proportional in quantity to the reconstituted amounts of FAD-APP. Consistent with the dominant inheritance of this type of FAD, this function was dominant over normal APP, because little activation was observed in APP695-GO vesicles. Experiments with antibody competition and sequence deletion indicated that His657-Lys676 of FAD-APP, which has been specified as the ligand-dependent GO-coupling domain of normal APP, was responsible for this constitutive activation, confirming that the three FAD-APPs are mutationally activated APP695. This study identifies the intrinsic signaling function of APP to be a novel target of hereditary Alzheimer's disease mutations, providing an in vitro system for the screening of potential FAD inhibitors.

Alzheimer Disease↗
PubMed1996

Synergistic activation of PtdIns 3-kinase by tyrosine-phosphorylated peptide and beta gamma-subunits of GTP-binding proteins.

Stimulation of differentiated THP-1 cells by insulin led to rapid accumulation of PtdIns(3,4,5)P3, a product of PtdIns 3-kinase. Stimulation of the GTP-binding-protein-linked receptor by N-formylmethionyl-leucyl-phenylalanine (fMLP) also induced the accumulation of PtdIns(3,4,5)P3 in the cells. The effect of insulin was, while that of fMLP was not, accompanied by increased PtdIns 3-kinase activity in the anti-phosphotyrosine immuno-precipitate. The combination of insulin and fMLP induced more PtdIns(3,4,5)P3 production than the sum of the individual effects. The insulin-induced recruitment of PtdIns 3-kinase activity in the anti-phosphotyrosine immunoprecipitate was unaffected by the combined treatment with fMLP. To investigate the mechanism underlying the synergistic accumulation of PtdIns(3,4,5)P3, we separated the cytosolic proteins of THP-1 cells on a Mono Q column. PtdIns 3-kinase activities were eluted in two peaks, and one of the peaks markedly increased on the addition of beta gamma-subunits of GTP-binding proteins (G beta gamma). The other peak was affected only slightly by G beta gamma, but was synergistically increased by G beta gamma and a tyrosine-phosphorylated peptide which was synthesized accordingly to the amino acid sequence of insulin receptor substrate-1. The activity in the latter fraction was completely immunoprecipitated by an antibody against the regulatory subunit of PtdIns 3-kinase (p85). These results suggest that the conventional PtdIns 3-kinase (p85/p110), which has been implicated in insulin-induced cellular events, or a closely related isoenzyme is controlled by a combination of a tyrosine-phosphorylated protein and a GTP-binding protein in intact cells.

Amino Acid Sequence↗
PubMed1996

Stimulation of ADP-ribosyl cyclase activity of the cell surface antigen CD38 by zinc ions resulting from inhibition of its NAD+ glycohydrolase activity.

The lymphocyte cell surface antigen, CD38, which has an amino acid sequence similar to Aplysia ADP-ribosyl cyclase, catalyzes not only the hydrolysis of NAD+ and 1-(5-phospho-beta-D-ribosyl) adenosine 5'-phosphate cyclic anhydride (cyclic ADP-ribose) but also the formation of cyclic ADP-ribose from NAD+. To characterize the bifunctional enzyme properties, we produced the recombinant CD38 fused with a maltose-binding protein (MBP-CD38). Zinc ions stimulated the ADP-ribosyl cyclase activity of MBP-CD38, but inversely inhibited its NAD+ glycohydrolase activity which was approximately 100-fold dominant to the cyclase activity in the absence of Zn2+. Such dual effects of Zn2+ were also observed in the native membrane-bound CD38 of HL-60 cells which had been caused to differentiate by retinoic acid. Zinc ions inhibited the NAD+ glycohydrolase reaction catalyzed by MBP-CD38 in an uncompetitive manner, whereas they enhanced the ADP-ribosyl cyclase reaction without affecting the Km value for NAD+. There was an increase in the fluorescence intensity of a hydrophobic fluorescent probe, 8-anilino-1-naphthalenesulfonate, in the presence of MBP-CD38. The fluorescence increase was further enhanced by the addition of Zn2+ with a shift in the maximum emission wavelength from 484 nm to 470 nm, suggesting that Zn2+ caused conformational changes of MBP-CD38. These results indicate that Zn2+ directly interacts with CD38 to stimulate its ADP-ribosyl cyclase with inhibition of its NAD+ glycohydrolase, probably due to prevention of the access of water molecule to an intermediate of the enzymesubstrate complex.

ADP-ribosyl Cyclase↗
PubMed1996

Increase in ADP-ribosyltransferase activity of rat T lymphocyte alloantigen RT6.1 by a single amino acid mutation.

A family of glycosylphosphatidylinositol-linked ADP-ribosyltransferases, of which cDNAs were cloned from various mammalian cells, possess a common Glu-rich motif (EEEVLIP) near their carboxyl termini. Although the first Glu in the common motif is replaced by Gln (Q207EEVLIP) in rat T lymphocyte alloantigens RT6.1 and RT6.2, the two RT6s appear to have both activities of NAD+ glycohydrolase and ADP-ribosyltransferase to a lesser extent. To investigate the significance of the Glu-rich motif in the two enzyme activities, we produced a mutant RT6.1 (Q207E), in which Gln207 was replaced by Glu, together with wild-type RT6s, in Escherichia coli. Kinetic analysis revealed that there were no marked differences in the Vmax and Km values of NAD+ glycohydrolases among the three recombinant proteins. The recombinant RT6.1 and RT6.2 displayed extremely low auto-ADP-ribosylation, although the latter modification was somewhat higher than the former. In contrast, much greater auto-modification was observed for the Q207E mutant. Moreover, the mutant could effectively ADP-ribosylate agmatine as a substrate. Thus, the single amino acid mutation of RT6.1 caused a marked increase in its ADP-ribosyltransferase activity, indicating that the Glu-rich motif near the carboxy terminus plays an important role in the enzyme activity.

ADP Ribose Transferases↗
PubMed1996

Inhibition of NAD+ glycohydrolase and ADP-ribosyl cyclase activities of leukocyte cell surface antigen CD38 by gangliosides.

We have recently reported that gangliosides act as inhibitors of ADP-ribosyltransferases and NAD+ glycohydrolases (NADase) of pertussis toxin and the C3 exoenzyme from Clostridium botulinum (Hara-Yokoyama, M., Hirabayashi, Y., Irie, F., Syuto, B., Moriishi, K., Sugiya, H., and Furuyama, S. (1995) J. Biol. Chem. 270, 8115-8121). Here, we investigated the effect of gangliosides on the enzymatic activity of leukocyte cell surface antigen CD38, which is identified as an ecto-NADase (Kontani, K., Nishina, H., Ohoka, Y., Takahashi, K., and Katada, T. (1993) J. Biol. Chem. 268, 16895-16898). Gangliosides GM1a and GQ1balpha inhibited the NADase activity in the immunoprecipitate of anti-CD38 antibody from the membrane extract of retinoic acid-treated human leukemic HL-60 cells. Gangliosides also inhibited the NADase activity of the extracellular domain of CD38 antigen that was deprived of the transmembrane domain and was expressed in Escherichia coli as a fusion protein with maltose-binding protein (MBP-CD38). The order of the inhibitory effect of purified ganglioside species on the NADase activity on MBP-CD38 was as follows: GQ1balpha > GT1b, GQ1b > GD1a, GD1b, GM1a, GM1b, GD3, GM3. GQ1balpha inhibited the NADase of MBP-CD38 in a noncompetitive manner versus NAD+ with a Ki value of about 0.3 microM. Neither ceramide nor the oligosaccharide moiety of GQ1balpha had an effect on the NADase activity. GQ1balpha, GT1b, and GQ1b also efficiently inhibited the ADP-ribosyl cyclase activity of MBP-CD38. At present, gangliosides are the only endogenous species that can block the enzymatic activity of CD38 antigen. The present results suggest a potential role of gangliosides as inhibitors of the ecto-NADases.

ADP-ribosyl Cyclase↗