Biomedical subjects

A Zweibaum

Publications and source records attributed to A Zweibaum.

At least 19 recordsLinked to original sources

PubMed1992

Expression and characterization of mucins associated with the resistance to methotrexate of human colonic adenocarcinoma cell line HT29.

A series of experiments were conducted to study synthesis and secretion of mucin in mucus-secreting subpopulations of HT29 human colonic adenocarcinoma cells selected by resistance to methotrexate (MTX). Mucin was quantitated by [3H]glucosamine labeling and chromatography on Sepharose CL-4B. The mucinous nature of the labeled high molecular weight glycoprotein was verified by alkaline borohydride treatment, cesium chloride density gradient ultracentrifugation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The results of these experiments demonstrated that MTX-treated cells have increased amounts of mucin in medium, cytosol, and membrane fractions. This was associated with the increase in the activities of polypeptidyl-N-acetylgalactosaminyltransferase and beta-1,3-galactosyltransferase compared to control cells. DEAE-Sephacel chromatography of [3H]glucosamine-labeled high molecular weight glycoproteins suggest that MTX-treated cells are less acidic compared to controls. Using complementary DNA probes for two distinct human intestinal mucins (MUC2 and MUC3) and one mammary mucin (MUC1), it was found that MTX-treated cells expressed more mucin messages compared to untreated cells. These results were consistent with immunoblots using anti-MRP (MUC2 repeat peptide), anti-M3P (MUC3 repeat peptide), 139H2 (MUC1 peptide), anti-T (peanut lectin), anti-Tn (91S8), and anti-sialosyl Tn (JT10e) antibodies. These data indicate that MTX-resistant HT29 cells show enhanced secretion and synthesis of mucin as well as expression of MUC1-, MUC2-, and MUC3-related mucin polypeptide epitopes.

Cell Differentiation↗

PubMed1992

Expression and localization of GLUT-5 in Caco-2 cells, human small intestine, and colon.

The human colon carcinoma cell line Caco-2 was used as an enterocyte model to study the expression of the facilitative glucose transporters GLUT-1 and GLUT-2, and of the putative hexose transporter GLUT-5, which are expressed specifically in the gut. Northern blots indicate that Caco-2 cells express GLUT-1 and GLUT-5 mRNAs but not the mRNA coding for the basolateral glucose transporter GLUT-2. The level of GLUT-5 mRNA is growth dependent, being detectable only in postconfluent differentiated cells. In addition, the expression of GLUT-5 increases with the number of cell passages and is approximately 10 times higher in later passages (passage 184) than in early ones (passage 26). With the use of polyclonal antibodies directed against the COOH-terminus of GLUT-5, indirect immunofluorescence and Western blotting indicate that GLUT-5 is mainly localized to the brush border of Caco-2 cells. GLUT-5 is also found to be associated with the brush border of epithelial cells from fetal and normal adult human small intestine, but is absent from the colon.

Adult↗

PubMed1991

Synthesis and secretion of a cobalamin-binding protein by HT 29 cell line.

An HT 29 cell line derived from human colonic carcinoma was shown to synthesize and release a cobalamin-binding protein. The cobalamin-binding protein was classified as transcobalamin (TC). By gel filtration on Sephacryl S200 HR, we observed that the secreted protein bound to cobalamin had the same size as plasma transcobalamin. Like transcobalamin, the cobalamin-binding protein bound cobalamin but not cobinamide. Purification of the cobalamin-binding protein was performed by heparin-Sepharose affinity chromatography and by Sephacryl S200 gel filtration. The molecular mass of the purified protein was estimated at 44 kDa by SDS/PAGE. The isoelectric point was determined to be 6.4. The purified cobalamin-binding protein reacted with an antiserum produced against human transcobalamin. A 44 kDa band was also identified by SDS/PAGE of an immunoprecipitated homogenate from HT 29 cells labelled with [35S]methionine and in a Western blot of cell homogenates. The secretion of the cobalamin-binding protein was maximal between 10 and 12 days of cell culture and was inhibited by cycloheximide.

Blotting, Western↗

PubMed1991

Adaptation to 5-fluorouracil of the heterogeneous human colon tumor cell line HT-29 results in the selection of cells committed to differentiation.

The HT-29 cell line contains a small proportion of differentiated polarized, enterocytic and mucus-secreting cell types (less than 95%) which can be selected under various pressure conditions, e.g., glucose deprivation or methotrexate. The purpose of the present work was to investigate whether this also applies to 5-fluorouracil (FUra). Stepwise adaptation of exponentially growing cells to 1, 5, 10 and 20 microM FUra results, after a phase of high mortality, in the emergence of adapted sub-populations with stable growth rates and curves, and IC50 6, 18, 37, and 110 times higher than in untreated cells respectively. FUra-adapted cells are all differentiated, according to 2 phenotypes: (I) polarized dome-forming cells which express carcinoembryonic antigen at their apical surface and (2) goblet cells which secrete a mucus of colonic immunoreactivity. These phenotypes are present in the parental population and are different from those selected e.g., by glucose deprivation or methotrexate. This differentiation pattern is maintained when the cells are subcultured in drug-free medium. Resistance to FUra is acquired through gene amplification as substantiated by a 4- to 6-fold increase of thymidylate synthase gene copies in cells stably adapted to the drug. Whether the same mechanism or others are responsible for the first steps of resistance to FUra remains to be elucidated. Altogether, these results support the hypothesis that some of the cells which are present in the parental line and are committed to differentiation possess advantages which allow them to immediately resist and secondarily adapt to FUra. Comparison of the differentiation characteristics of FUra-adapted cells with those from cells selected under other pressure conditions suggests that resistance and adaptation to either type of pressure may depend on the differentiated phenotype to which the cells are committed.

Blotting, Northern↗

PubMed1991

Increased growth adaptability to 5-fluorouracil and methotrexate of HT-29 sub-populations selected for their commitment to differentiation.

Adaptation of the heterogeneous human colon carcinoma cell line HT-29 to lethal concentrations of methotrexate (MTX) and 5-fluorouracil (FUra) was shown to result in the emergence of sub-populations of cells all stably committed to differentiation. It was postulated that these populations result from selection of a few cells present in the parental line which possess, associated with their ability to differentiate, particular advantages allowing them to adapt to adverse conditions such as MTX or FUra. The purpose of the present study was to further verify this hypothesis by investigating whether HT-29 sub-populations selected for the commitment of all cells to differentiation would spontaneously be more resistant and adaptable than the parental cells to MTX and FUra. This study included a mucus-secreting clone (HT29-16E), a transporting clone (HT29-19A), and an enterocytic population selected by glucose deprivation (HT29-Glc-/+). Although all 3 populations show only a slight increase in their spontaneous resistance to both drugs, as substantiated by the values of IC50 which are only less than 2-fold higher than in parental cells, they are more adaptable as judged by growth curves, over a 50-day culture period, under exposure to 1 microM FUra and 0.1 microM MTX. In sharp contrast to parental cells, which, at these concentrations, show a high rate of mortality, all 3 populations, although growing slowly, reach densities more or less close, depending on the drug and population concerned, to that of control untreated cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Differentiation↗

PubMed1991

Dihydrofolate reductase gene amplification-associated shift of differentiation in methotrexate-adapted HT-29 cells.

Postconfluent cultures of HT-29 cells form a heterogeneous multilayer of which greater than 95% of the cells are undifferentiated. In contrast, when stably adapted to normally lethal concentrations of methotrexate (10(-6)-10(-5) M), they form a monolayer of gobletlike cells (Lesuffleur et al., 1990) which secrete large quantities of mucins and display a discrete brush border with the presence of villin, dipeptidylpeptidase-IV, and carcinoembryonic antigen. When adapted to even higher concentrations of methotrexate (10(-4) and 10(-3) M) there is a shift in the pattern of differentiation from gobletlike to dome-forming absorptive-like cells. These cells still display an apical brush border which expresses villin and dipeptidylpeptidase-IV, but no longer express significant levels of mucins and carcinoembryonic antigen. This shift of differentiation coincides with a sudden amplification of the gene coding for dihydrofolate reductase and an increased activity of the enzyme.

Blotting, Southern↗

PubMed1990

Growth adaptation to methotrexate of HT-29 human colon carcinoma cells is associated with their ability to differentiate into columnar absorptive and mucus-secreting cells.

The purpose of this work was to investigate whether the phenomenon of metabolic adaptation of HT-29 cells to glucose deprivation and subsequent emergence of differentiated subpopulations (A. Zweibaum et al., J. Cell. Physiol., 122: 21-29, 1985) also applies to anticancer drugs that act at a metabolic level like methotrexate (MTX). Stepwise adaptation of exponentially growing HT-29 cells to increasing concentrations of MTX (10(-7), 10(-6), and 10(-5) mol) results, after a phase of high mortality, in the emergence of subpopulations with stable growth rates and curves close to those of untreated control cells. In contrast to control cells which are heterogenous and contain, after confluency, only a small proportion of differentiated cell types (less than 4%), postconfluent cultures of MTX-adapted cells are totally differentiated. Cells adapted to 10(-7) M MTX form a mixed population of columnar absorptive and mucus cells; at higher concentrations cells are almost exclusively of the mucus-secreting type. All cells, whether mucus-secreting or not, develop an apical brush border which strongly expresses dipeptidylpeptidase IV, carcinoembryonic antigen, and villin. These differentiation features, which resemble those of fetal colon, are associated with decreased rates of glucose consumption and lactic acid production. Both differentiation characteristics and metabolic changes are stably maintained when the cells are subcultured in the absence of the drug. Like the original population, MTX-adapted cells are tumorigenic in nude mice. We propose that cells which are able to differentiate and which are the origin of the small proportion of differentiated cell types found in postconfluent cultures of the original cell line possess an advantage which allows them to be adaptable to "metabolic stress" conditions.

Carcinoma↗

PubMed1990

N-glycosylation modification of proteins is an early marker of the enterocytic differentiation process of HT-29 cells.

The human colon cancer cell line HT-29 remains totally undifferentiated when glucose is present in the culture medium (HT-29 Glc+), while the same cells may undergo typical enterocytic differentiation after reaching confluence when grown in glucose-deprived medium (HT-29 Glc-). Recently, we demonstrated a deficiency in the overall N-glycan processing in confluent undifferentiated cells, whereas differentiated cells follow a classical pattern of N-glycosylation. The main changes in N-glycosylation observed in confluent undifferentiated cells may be summarised as follows: 1) the conversion of high mannose into complex glycopeptides is greatly decreased; 2) this decreased conversion could be a consequence of an accumulation of Man9-8-GlcNAc2-Asn high mannose species. Whether these changes in N-glycan processing appear progressively during cell culture or are already present from the beginning of the culture was investigated in this study by comparing the actual status of N-glycan processing in exponentially growing HT-29 Glc- and HT-29 Glc+ cells. Under these conditions, HT-29 Glc- cells do not exhibit any characteristics of differentiation. The conversion of high mannose into complex glycoproteins is severely reduced in HT-29 Glc+ cells, regardless of the growth phase studied. In contrast, HT-29 Glc- cells display a normal pattern of N-glycan processing in both growth phases. We therefore conclude that N-glycan processing may be used as an early biochemical marker of the enterocytic differentiation process of HT-29 cells.

Cell Differentiation↗

PubMed1989

Sucrase-isomaltase expression and enterocytic ultrastructure of human colorectal tumors.

We report the relative frequency of sucrase-isomaltase (SI) antigen expression in human colonic adenocarcinoma (22/57), in peritumoral mucosa taken next to the tumor (31/41) or distant from it (29/42) as well as in 21/23 polyps. Our results are based on indirect immunofluorescence with a monoclonal antibody (MAb) specific for human intestinal SI. A regular and intense expression of SI occurred only in 6 tumor specimens. In the remaining 16 SI-positive tumor samples, labelling was heterogeneous, i.e., scattered over more or less extensive areas. A similar irregular staining pattern was also found in polyps and in peritumoral mucosa, irrespective of its distance from the tumor. Electron microscopic examination of 19 carcinomas mostly revealed altered brush-border membrane features, irrespective of histological SI staining pattern. Brush-border enzyme activities of sucrase, alkaline phosphatase and maltase showed no difference between tumor specimens and peritumoral mucosa, but aminopeptidase was depressed in the former. Sucrase activity was extremely low (mean values 1.1 to 1.8 mU/mg protein) and rose only exceptionally to 17.5 mU/mg prot.

Adenocarcinoma↗

PubMed1989

Processing of asparagine-linked oligosaccharides is an early biochemical marker of the enterocytic differentiation of HT-29 cells.

The inability of HT-29 cells to undergo an enterocytic differentiation when grown in a glucose-containing (Glc+) medium has been recently correlated to an overall impairment of N-glycan processing. These results were obtained using confluent HT-29 cells in which the differentiation characteristics are fully expressed under differentiation permissive conditions (glucose-deprived medium, Glc-). Whether these changes of N-glycan processing appear progressively during the cell growth or are already present from the beginning of the culture was investigated in this work by comparing the actual status of N-glycan processing in both exponentially growing Glc+ and Glc- HT-29 cells. Under these conditions, HT-29 cells do not express any characteristics of enterocytic differentiation, even when grown in differentiation permissive conditions. We show here that the conversion of high-mannose to complex glycoproteins is, however, severely reduced in HT-29 cells grown in differentiation non-permissive conditions (HT-29 Glc+) whatever the phase of growth studied. In contrast, HT-29 cells grown in differentiation permissive conditions (HT-29 Glc-) display a normal pattern of N-glycan processing in both the exponential and the stationary phase of growth. We also show that both growing and confluent HT-29 Glc+ cells accumulate Man GlcNAc2 species, thus suggesting that there is an important regulatory point at this level. We therefore conclude that the N-glycan processing may be used as an early biochemical probe for the enterocytic differentiation of HT-29 cells. Whether these early changes result from an early metabolic regulation or are the consequence of a genetic control remains to be studied.

Asparagine↗

PubMed1989

Reversible forskolin-induced impairment of sucrase-isomaltase mRNA levels, biosynthesis, and transport to the brush border membrane in Caco-2 cells.

Hybridization analysis of mRNA with a cDNA probe for human sucrase-isomaltase, pulse-chase experiments with L-[35S]-methionine followed by SDS-PAGE, and immunofluorescence detection of sucrase-isomaltase were used to analyze the level(s) at which forskolin interferes with the expression of the enzyme in Caco-2 cells in culture. Three effects are observed in Caco-2 cells treated with forskolin: 1) a marked decrease in the level of sucrase-isomaltase mRNA, 2) a marked decrease in the biosynthesis of the enzyme without any alteration of its stability, and 3) an almost total inhibition of its transport to the brush border membrane. All three effects are reversible when the drug is removed from the culture medium, though this reversibility is asynchronous: transport to the brush border membrane resumes after 24 h, sucrase-isomaltase mRNA levels are back to the normal after 5 days, whereas the biosynthesis of the enzyme, although increasing progressively, remains lower than in control cells, even 10 days after removal of the drug. The possibility that some effects are directly dependent on cAMP and others a consequence of changes in glucose metabolism is discussed.

Biological Transport↗

PubMed1988

Monensin inhibits the expression of sucrase-isomaltase in Caco-2 cells at the mRNA level.

Using L-[35S]methionine labeling, SDS-PAGE and Northern blot analysis of sucrase-isomaltase mRNA, two different concentrations of monensin were used to delineate in Caco-2 cells the effect of the drug on the conversion of the high mannose to the complex form of sucrase-isomaltase from its dual effect on the biosynthesis of the enzyme and on the rate of glucose consumption. At 0.1 microM the drug has no effect on the rate of glucose consumption and, although it inhibits the conversion of the high mannose to the complex form of the enzyme, it has no effect on the level of sucrase-isomaltase mRNA and on the amount of neosynthesized enzyme. At 1 microM, in addition to its inhibiting effect on the maturation of the enzyme, monensin provokes concomitantly an increase in the rate of glucose consumption and a decrease in the level of sucrase-isomaltase mRNA and in the amount of neosynthesized enzyme. All these effects are reversible within 48 h after removal of the drug.

Colonic Neoplasms↗

PubMed1988

Epithelial polarity, villin expression, and enterocytic differentiation of cultured human colon carcinoma cells: a survey of twenty cell lines.

Twenty human colon carcinoma cell lines were studied for their ability to develop some of the characteristics of the normal intestinal epithelium, e.g., epithelial polarity, presence of the actin-binding protein villin, or the occurrence of an enterocytic differentiation either when cultured under standard conditions, as for Caco-2 cells, or when grown in a glucose-free medium, as for HT-29 cells. Except for the regular presence of villin, which can be considered a marker of the colonic origin of the cells, the cell lines of this study could be classified into four types with regard to their differentiation characteristics. In type 1 (only one cell line, i.e., Caco-2) the cells undergo spontaneously an enterocytic differentiation characterized by a polarization of the cell layer with the formation of domes and the presence of an apical brush border the membrane of which is endowed with hydrolases such as sucrase-isomaltase, lactase, amino-peptidase N, dipeptidylpeptidase IV and alkaline phosphatase. In type 2 (three cell lines: HT-29, HCT-EB, and HCT-GEO) the cells are undifferentiated when grown in the presence of glucose but undergo an enterocytic differentiation when grown in the absence of glucose. In type 3 (eight cell lines: HCT-GLY, HCT-FET, HCT-FRI, HCT-CBS, HCT-ALA, Co-115, HRT-18, and SW-1116) the cells are organized into a polarized monolayer with the formation of domes but without any enterocytic differentiation characteristics, whatever the culture conditions. In type 4 (eight cell lines: HCT-116a, HCT-R, HCT-RCA, HCT-Moser, HCT-8R, SW-480, LS-174T, and Vaco-9P) the cells are organized into a multilayer without any feature of epithelial polarity or enterocytic differentiation, whatever the culture conditions.

Carcinoma↗

PubMed1987

Development of vasoactive intestinal peptide-responsive adenylate cyclase during enterocytic differentiation of Caco-2 cells in culture. Evidence for an increased receptor level.

The purpose of this work was to study vasoactive intestinal peptide (VIP) receptors and the adenylate cyclase response to VIP upon enterocytic differentiation of the human colon adenocarcinoma cell line Caco-2 in culture. The VIP-stimulated enzyme activity is very low, e.g. 20% above basal activity in undifferentiated cells (day 5) and is enhanced markedly at confluency reaching a maximum, e.g. 270%, above basal activity in fully differentiated cells (day 30). VIP potency is also slightly enhanced, the EC50 of VIP ranging from 0.31 nM at day 5 to 0.07 nM at day 30. Modifications of the adenylate cyclase system are not responsible for the development of VIP response. Indeed, forskolin-stimulated adenylate cyclase activity is unchanged during differentiation supporting no alteration of the enzyme catalytic subunit. The same holds true for NaF and guanosine 5'-(beta, gamma-imido)trisphosphate, indicating a constant activity of the guanine nucleotide regulatory unit which mediates hormonal stimulation of adenylate cyclase (Ns). This is further supported by the similar extent of cholera toxin-catalyzed [32P]ADP-ribosylation of the Ns protein that is observed during differentiation. In sharp contrast, a dramatic increase of VIP receptor concentration is observed ranging from 32 fmol/mg of protein at day 5 to 414 fmol/mg of protein at day 30. This is confirmed by affinity cross-linking experiments showing an increased specific incorporation of 125I-VIP in a major 66,000-dalton component during differentiation. A slight increase in receptor affinity is also observed during differentiation with Kd ranging from 0.39 nM at day 5 to 0.08 nM at day 30. These data indicate that one population of VIP receptors accumulates during Caco-2 cell differentiation, representing the crucial event in the development of adenylate cyclase response to the peptide.

Adenylyl Cyclases↗

PubMed1987

A and H blood group antigens as markers of sucrase-isomaltase from the enterocyte-like differentiated human colon carcinoma cell lines HT-29 and Caco-2.

The purpose of this work was to investigate whether sucrase-isomaltase from enterocyte-like differentiated human colon carcinoma cell lines carries blood group antigens of the ABH system. Six cultured lines of blood group A (HT-29, SW-480, Co-115) or O phenotype (Caco-2, HRT-18, HCT-8R) were studied. Only HT-29 cells grown in the absence of glucose (HT-29 Glc-) and Caco-2 cells express an enterocytic differentiation with the presence of sucrase-isomaltase on the apical surface of the cells. Binding of anti-A antibodies to HT-29 Glc- and of UEA-I to Caco-2 cells gave the same apical immunofluorescence pattern of staining as did anti-sucrase-isomaltase antibodies, whereas only a membrane binding was observed in nondifferentiated cells. Sucrase-isomaltase immunoisolated from HT-29 Glc- and Caco-2 cells reacted with anti-A antibodies and Ulex europaeus agglutinin-I (UEA-I), respectively, at sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot. Immunoprecipitation of solubilized brush border-enriched fractions from the same cells with UEA-I or anti-A antibodies resulted in an inhibition of sucrase activity which reached congruent to 80% for Caco-2 cells with UEA-I and approximately equal to 50% for HT-29 cells with anti-A antibodies. Similar results were obtained in the corresponding tumors in nude mice: anti-A antibodies in HT-29 and UEA-I in Caco-2 tumors bound to the same apical structures as did anti-sucrase-isomaltase antibodies; sucrase-isomaltase immunoisolated from the tumors bound anti-A antibodies (HT-29) or UEA-I (Caco-2). These results support the hypothesis that sucrase-isomaltase from enterocyte-like differentiated human colon cancer cells carries blood group antigens of the ABH system. These findings suggest that colon cancers which have been shown to display an apical pattern of expression of ABH antigens should be screened for their possible enterocytic differentiation.

ABO Blood-Group System↗

PubMed1987

The posttranslational processing of sucrase-isomaltase in HT-29 cells is a function of their state of enterocytic differentiation.

The biosynthesis of sucrase-isomaltase was compared in enterocyte-like differentiated (i.e., grown in the absence of glucose) and undifferentiated (i.e., grown in the presence of glucose) HT-29 cells. Unlike differentiated cells, in which the enzyme is easily detectable and active, undifferentiated cells display almost no enzyme activity and the protein cannot be detected by means of cell surface immunofluorescence or immunodetection in membrane-enriched fractions or cell homogenates. Pulse experiments with L-[35S]-methionine show that the enzyme is, however, synthesized in these undifferentiated cells. As compared with the corresponding molecular forms in differentiated cells, the high-mannose form of the enzyme in undifferentiated cells is similarly synthesized and has the same apparent Mr. However, its complex form is less labeled and has a lower apparent Mr. Pulse-chase experiments with L-[35S]methionine show that, although the enzyme is synthesized to the same extent in both situations, the high-mannose and complex forms are rapidly degraded in undifferentiated cells, with an apparent half-life of 6 h, in contrast to differentiated cells in which the enzyme is stable for at least 48 h. A comparison of the processing of the enzyme in both situations shows that the conversion of the high-mannose to the complex form is markedly decreased in undifferentiated cells. These results indicate that the absence of sucrase-isomaltase expression in undifferentiated cells is not the consequence of an absence of biosynthesis but rather the result of both an impaired glycosylation and a rapid degradation of the enzyme.

Antibodies, Monoclonal↗

PubMed1986

Inhibition of the post-translational processing of microvillar hydrolases is associated with a specific decreased expression of sucrase-isomaltase and an increased turnover of glucose in Caco-2 cells treated with monensin.

The biosynthesis and post-translational processing of sucrase-isomaltase and dipeptidylpeptidase IV were studied by L-[35S]methionine labeling, immunoisolation with monoclonal antibodies and SDS-PAGE in post-confluent Caco-2 cells treated with monensin (10 microM, 48 h). In addition to its classical effect on the post-translational processing of both hydrolases, i.e. an inhibition of the conversion of the high-mannose to the complex glycosylated form of the enzymes, monensin was found to have two other effects: a marked decrease of sucrase-isomaltase expression, but not of dipeptidylpeptidase IV; an increased turnover of glucose, as substantiated by increased rates of glucose consumption and lactic acid production and a decreased glycogen content. Whether these two effects are related to the particular differentiation and metabolic status of Caco-2 cells is discussed, as well as a possible role for the drug-induced modifications of glucose turnover on the decreased expression of sucrase-isomaltase.

Cell Line↗

PubMed1986

Castanospermine: a potent inhibitor of sucrase from the human enterocyte-like cell line Caco-2.

The addition of castanospermine (5-50 microM) to a culture medium of Caco-2 cells results in a specific suppression of sucrase activity without modification of the biosynthesis of the enzyme. This effect is due to a direct inhibiting effect of castanospermine on Caco-2 sucrase activity. This inhibition is time-dependent (half-maximum efficiency at 10 min for 100 nM), enhanced by preincubation (suggesting a strong interaction with the enzyme), dose-dependent (ED50 at 4 nM after 1 h preincubation period) and of the fully non-competitive type. The calculated Ki (2.6 nM) suggests that castanospermine is the most potent inhibitor of sucrase so far reported.

Alkaloids↗