New application of a traditional method: colorimetric sensor array for reducing sugars based on the in-situ formation of core-shell gold nanorod-coated silver nanoparticles by the traditional Tollens reaction.

An effective and robust colorimetric sensor array for simultaneous detection and discrimination of five reducing sugars (i.e., glyceraldehyde (Gly), fructose (Fru), glucose (Glu), maltose (Mal), and ribose (Rib)) has been proposed. In the sensor array, two negatively charged polydielectrics (sodium polystyrenesulfonate (NaPSS) and sodium polymethacrylate (NaPMAA)), which served as the sensing elements, were individually absorbed on the surface of the cetyltrimethylammonium bromide (CTAB)-coated gold nanorods (AuNR) with positive charges through electrostatic action, forming the designed sensor units (NaPSS-AuNR and NaPMAA-AuNR). In the presence of Tollens reagent (Ag(NH3)2OH), Ag+ was absorbed on the surface of negatively charged NaPSS-AuNR and NaPMAA-AuNRs. When confronted with differential reducing sugars, different reducing sugars exhibited differential levels of deoxidizing abilities toward Ag+, thus Ag+ was reduced to diverse amounts of silver nanoparticles (AgNPs) in situ to form core-shell AuNR@AgNP by the traditional Tollens reaction method, leading to distinct colorimetric response patterns (value of AS/AL (the ratio of absorbance at 360 nm to that at 760 nm in Ag+-NaPMAA-AuNR, and the ratio of absorbance at 360 nm to that at 740 nm in Ag+-NaPSS-AuNR)). These response patterns are characteristic for each reducing sugar, and can be quantitatively distinguished by linear discriminant analysis (LDA) at concentrations as low as 10 nM with relative standard deviation (RSD) of 4.11% (n = 3). The practicability of this sensor array has been validated by recognition of reducing sugars in serum and urine samples. A colorimetric sensor array for reducing sugar discrimination based on the reduction of Ag+ and in situ formation of AuNR@AgNP.

Synthesis of [¹8F]-labelled maltose derivatives as PET tracers for imaging bacterial infection.

PURPOSE: To develop novel positron emission tomography (PET) agents for visualization and therapy monitoring of bacterial infections. PROCEDURES: It is known that maltose and maltodextrins are energy sources for bacteria. Hence, (18)F-labelled maltose derivatives could be a valuable tool for imaging bacterial infections. We have developed methods to synthesize 4-O-(α-D-glucopyranosyl)-6-deoxy-6-[(18)F]fluoro-D-glucopyranoside (6-[(18)F]fluoromaltose) and 4-O-(α-D-glucopyranosyl)-1-deoxy-1-[(18)F]fluoro-D-glucopyranoside (1-[(18)F]fluoromaltose) as bacterial infection PET imaging agents. 6-[(18)F]fluoromaltose was prepared from precursor 1,2,3-tri-O-acetyl-4-O-(2',3',-di-O-acetyl-4',6'-benzylidene-α-D-glucopyranosyl)-6-deoxy-6-nosyl-D-glucopranoside (5). The synthesis involved the radio-fluorination of 5 followed by acidic and basic hydrolysis to give 6-[(18)F]fluoromaltose. In an analogous procedure, 1-[(18)F]fluoromaltose was synthesized from 2,3, 6-tri-O-acetyl-4-O-(2',3',4',6-tetra-O-acetyl-α-D-glucopyranosyl)-1-deoxy-1-O-triflyl-D-glucopranoside (9). Stability of 6-[(18)F]fluoromaltose in phosphate-buffered saline (PBS) and human and mouse serum at 37 °C was determined. Escherichia coli uptake of 6-[(18)F]fluoromaltose was examined. RESULTS: A reliable synthesis of 1- and 6-[(18)F]fluoromaltose has been accomplished with 4-6 and 5-8% radiochemical yields, respectively (decay-corrected with 95 % radiochemical purity). 6-[(18)F]fluoromaltose was sufficiently stable over the time span needed for PET studies (∼96% intact compound after 1-h and ∼65% after 2-h incubation in serum). Bacterial uptake experiments indicated that E. coli transports 6-[(18)F]fluoromaltose. Competition assays showed that the uptake of 6-[(18)F]fluoromaltose was completely blocked by co-incubation with 1 mM of the natural substrate maltose. CONCLUSION: We have successfully synthesized 1- and 6-[(18)F]fluoromaltose via direct fluorination of appropriate protected maltose precursors. Bacterial uptake experiments in E. coli and stability studies suggest a possible application of 6-[(18)F]fluoromaltose as a new PET imaging agent for visualization and monitoring of bacterial infections.

Factors interfering with the accuracy of five blood glucose meters used in Chinese hospitals.

BACKGROUND: The prevalence of diabetes is increasing in China. Glucose control is very important in diabetic patients. The aim of this study was to compare the accuracy of five glucose meters used in Chinese hospitals with a reference method, in the absence and presence of various factors that may interfere with the meters. METHODS: Within-run precision of the meters was evaluated include Roche Accu-Chek Inform®, Abbott Precision PCx FreeStyle®, Bayer Contour®, J&J LifeScan SureStep Flexx®, and Nova Biomedical StatStrip®. The interference of hematocrit level, maltose, ascorbic acid, acetaminophen, galactose, dopamine, and uric acid were tested in three levels of blood glucose, namely low, medium, and high concentrations. Accuracy (bias) of the meters and analytical interference by various factors were evaluated by comparing results obtained in whole blood specimens with those in plasma samples of the whole blood specimens run on the reference method. Impact of oxygen tension on above five blood glucose meters was detected. RESULTS: Precision was acceptable and slightly different between meters. There were no significant differences in the measurements between the meters and the reference method. The hematocrit level significantly interfered with all meters, except StatStrip. Measurements were affected to varying degrees by different substances at different glucose levels, e.g. acetaminophen and ascorbic acid (Freestyle), maltose and galactose (FreeStyle, Accu-Chek), uric acid (FreeStyle, Bayer Contour), and dopamine (Bayer Contour). CONCLUSIONS: The measurements with the five meters showed a good correlation with the plasma hexokinase reference method, but most were affected by the hematocrit level. Some meters also showed marked interference by other substances.

Investigating the response to intravenous iron in restless legs syndrome: an observational study.

OBJECTIVE: To investigate the effect of intravenous (IV) iron (500 mg ferric carboxymaltose [FCM] as a single dose) on restless legs syndrome (RLS) severity on a day-to-day basis. METHODS: Twenty patients with RLS and absolute or functional iron deficiency or low normal serum ferritin (<45 µg/l) were included. Change of RLS severity was evaluated using the International RLS severity scale (IRLS) and the RLS-severity diary (RLS-SD) which evaluates symptom severity over a 6-h period on an 11-point numerical Likert scale, four times a day. RESULTS: Twelve patients reported that IV FCM improved RLS ("responders"). IRLS score decreased from 30.1 (± 5.9) to 23.07 (± 9.5) (p=0.001) in the whole group and from 28.3 (± 6.1) to 18.3 (± 8.0) (p=0.002) in the responder group three weeks after IV FCM treatment. A clinically relevant effect of IV iron on RLS severity could be seen as early as day eight. The responder group differed from the non-responder group in tendency by being younger (p=0.064), having a lower serum ferritin level at baseline (p=0.097), and presenting a lower number of comorbid conditions. CONCLUSIONS: FCM led to a considerable improvement in RLS in the responder group within about one week. These findings are clinically relevant, especially for patients with severe RLS symptoms and iron deficiency, since a change or uptitration of RLS-specific medication can be avoided or postponed in these patients due to the rapid response to IV FCM treatment.

Iron status and analysis of efficacy and safety of ferric carboxymaltose treatment in patients with inflammatory bowel disease.

BACKGROUND AND AIMS: We analyzed iron deficiency and the therapeutic response following intravenous ferric carboxymaltose in a large single-center inflammatory bowel disease (IBD) cohort. METHODS: 250 IBD patients were retrospectively analyzed for iron deficiency and iron deficiency anemia. A subgroup was analyzed regarding efficacy and side effects of iron supplementation with ferric carboxymaltose. RESULTS: In the cohort (n = 250), 54.4% of the patients had serum iron levels ≤60 µg/dl, 81.2% had ferritin ≤100 ng/ml, and 25.6% had hemoglobin (Hb) of ≤12 g/dl (females) or ≤13 g/dl (males). In the treatment subcohort (n = 80), 83.1% of the patients had iron ≤60 µg/dl, 90.4% had ferritin ≤100 ng/ml, and 66.7% had Hb ≤12/13 g/dl before ferric carboxymaltose treatment. After a median dose of 500 mg ferric carboxymaltose, 74.7% of the patients reached iron >60 µg/dl, 61.6% had ferritin >100 ng/ml, and 90.7% reached Hb >12/13 g/dl at follow-up (p < 0.0001 for all parameters vs. pretreatment values). The most frequent adverse event was a transient increase of liver enzymes with male gender as risk factor (p = 0.008, OR 8.62, 95% CI 1.74-41.66). CONCLUSIONS: Iron deficiency and anemia are frequent in IBD patients. Treatment with ferric carboxymaltose is efficious, safe and well tolerated in iron-deficient IBD patients.

Estimates of total analytical error in consumer and hospital glucose meters contributed by hematocrit, maltose, and ascorbate.

BACKGROUND: Patients and physicians expect accurate whole blood glucose monitoring even when patients are anemic, are undergoing peritoneal dialysis, or have slightly elevated ascorbate levels. The objective of this study was to estimate analytical error in two consumer and two hospital glucose meters contributed by variations in hematocrit, maltose, ascorbate, and imprecision. METHODS: The influence of hematocrit (20-60%), maltose, and ascorbate were tested alone and in combination with each glucose meter and with a reference plasma glucose method at three concentrations of glucose. Precision was determined by consecutive analysis (n=20) at three levels of glucose. Multivariate regression analysis was used to estimate the bias associated with the interferences, alone and in combination. Total analytical error was estimated as |% bias|+1.96 (% imprecision). RESULTS: Three meters demonstrated hematocrit bias that was dependent upon glucose concentration. Maltose had profound concentration-dependent positive bias on the consumer meters, and the extent of maltose bias was dependent on hematocrit. Ascorbate produced small but statistically significant biases on three meters. Coincident low hematocrit, presence of maltose, and presence of ascorbate increased the observed bias and was summarized by estimation of total analytical error. Among the four glucose meter devices assessed, estimates of total analytical error in glucose measurement ranged from 6 to 68% under the conditions tested. CONCLUSIONS: The susceptibility of glucose meters to clinically significant analytical biases is highly device-dependent, and low hematocrit exacerbated the observed analytical error.

Interference studies with two hospital-grade and two home-grade glucose meters.

BACKGROUND: Interference studies of four glucose meters (Nova Biomedical [Waltham, MA] StatStrip [hospital grade], Roche Diagnostics [Indianapolis, IN] Accu-Chek Aviva [home grade], Abbott Diabetes Care [Alameda, CA] Precision FreeStyle Freedom [home grade], and LifeScan [Milpitas, CA] SureStep Flexx [hospital grade]) were evaluated and compared to the clinical laboratory plasma hexokinase reference method (Roche Hitachi 912 chemistry analyzer). These meters were chosen to reflect the continuum of care from hospital to home grade meters commonly seen in North America. METHODS: Within-run precision was determined using a freshly prepared whole blood sample spiked with concentrated glucose to give three glucose concentrations. Day-to-day precision was evaluated using aqueous control materials supplied by each vendor. Common interferences, including hematocrit, maltose, and ascorbate, were tested alone and in combination with one another on each of the four glucose testing devices at three blood glucose concentrations. RESULTS: Within-run precision for all glucose meters was <5% except for the FreeStyle (up to 7.6%). Between-day precision was <6% for all glucose meters. Ascorbate caused differences (percentage change from a sample without added interfering substances) of >5% with pyrroloquinolinequinone (PQQ)-glucose dehydrogenase-based technologies (Aviva and Freestyle) and the glucose oxidase-based Flexx meter. Maltose strongly affected the PQQ-glucose dehydrogenase-based meter systems. When combinations of interferences (ascorbate, maltose, and hematocrit mixtures) were tested, the extent of the interference was up to 193% (Aviva), 179% (FreeStyle), 25.1% (Flexx), and 5.9% (StatStrip). The interference was most pronounced at low glucose (3.9-4.4 mmol/L). CONCLUSIONS: All evaluated glucose meter systems demonstrated varying degrees of interference by hematocrit, ascorbate, and maltose mixtures. PQQ-glucose dehydrogenase-based technologies showed greater susceptibility than glucose oxidase-based systems. However, the modified glucose oxidase-based amperometric method (Nova StatStrip) was less affected in comparison with the glucose oxidase-based photometric method (LifeScan SureStep Flexx).

[Inaccuracy of glucose meters. Automatic correction for hematocrit variations and the presence of exogenous interfering components]. / Inexactitude des lecteurs de glycémie. Correction automatique pour les variations de l'hématocrite et la présence d'interférents exogènes.

Seven hospital-based glucose monitoring systems (meters) were evaluated with particular attention to those analytical interferences encountered in intensive care patients. Imprecision differed little between meters and remained altogether within acceptable limits. Inaccuracy, as measured by comparison with a hexokinase method presented with significant differences, yet without exceeding acceptable limits either. All meters but one showed an important bias when hematocrit departed from the reference interval. Two meters would not distinguish maltose from glucose. Three showed an important positive bias in the presence of acetaminophen and four a comparable bias in the presence of ascorbate. Only one meter was unaffected by both such exogenous interferences and hematocrit variations, owing to built-in hematocrit and electrochemical blank measuring devices. This meter also showed narrowest correlation with hexokinase methods. At a time when intensive care patients are being submitted to ever tighter glycemic control, it is desirable and our results show that it is now possible to tighten accordingly the acceptability criteria of glucose meters used to this end.

Hypoglycemic effect of 13-membered ring thiocyclitol, a novel alpha-glucosidase inhibitor from Kothala-himbutu (Salacia reticulata).

A novel 13-membered ring thiocyclitol, isolated from an aqueous extract of Kothala-himbutu (Salacia reticulata), inhibited alpha-glucosidase in vitro. The inhibitory activity was investigated by maltose- and sucrose-loading on Wistar rats. This study found significant lowering of postprandial glucose levels, and the potency of 13-membered ring thiocyclitol was confirmed in vivo.

[Analysis of maltose clearance in plasma and urine of healthy volunteers with high-performance liquid chromatography].

OBJECTIVE: To analyze the maltose clearance in plasma and urine of healthy volunteers with high-performance liquid chromatography. METHODS: Maltose solution was infused to 12 healthy volunteers during a 4-hour period at an infusion rate of 0.2, 0.3, and 0.5 g/(kg x h), Plasma and urine specimens were collected at different time points before and after infusion, and then analyzed with high-performance liquid chromatography. RESULTS: The coefficients of variation of the precision and accuracy of the analysis method ranged 3.68%-4.58% and 0.44%-4.83% for plasma, respectively, and 2.91%-7.62% and 0.95%-8.27% for urine, respectively. The plasma maltose concentration increased in a dose-dependent manner (r > 0.99). The plasma maltose concentrations returned to the baseline levels 12 hours later. Two hours after injection, the urinary excretion of maltose increased, reached the peak value within 2-4 hours, began to decrease 6 hours later, and became zero 24 hours later. CONCLUSIONS: An infusion rate of 0.2-0.5 g/(kg x h) of maltose will not remarkably increase the blood glucose level in healthy people. The routine infusion rate should below 0.3 g/(kg x h), unless an emergency exists.

Plasma-equivalent glucose at the point-of-care: evaluation of Roche Accu-Chek Inform and Abbott Precision PCx glucose meters.

BACKGROUND: Glucose testing at the bedside has become an integral part of the management strategy in diabetes and of the careful maintenance of normoglycemia in all patients in intensive care units. We evaluated two point-of-care glucometers for the determination of plasma-equivalent blood glucose. METHODS: The Precision PCx and the Accu-Chek Inform glucometers were evaluated. Imprecision and bias relative to the Vitros 950 system were determined using protocols of the Clinical Laboratory Standards Institute (CLSI). The effects of low, normal, and high hematocrit levels were investigated. Interference by maltose was also studied. RESULTS: Within-run precision for both instruments ranged from 2-5%. Total imprecision was less than 5% except for the Accu-Chek Inform at the low level (2.9 mmol/L). Both instruments correlated well with the comparison instrument and showed excellent recovery and linearity. Both systems reported at least 95% of their values within zone A of the Clarke Error Grid, and both fulfilled the CLSI quality criteria. The more stringent goals of the American Diabetes Association, however, were not reached. Both systems showed negative bias at high hematocrit levels. Maltose interfered with the glucose measurements on the Accu-Chek Inform but not on the Precision PCx. CONCLUSIONS: Both systems showed satisfactory imprecision and were reliable in reporting plasma-equivalent glucose concentrations. The most stringent performance goals were however not met.

Determination of several sugars in serum by high-performance anion-exchange chromatography with pulsed amperometric detection.

In this paper, a sensitive, simple and direct method for simultaneous determination of glucose, ribose, isomaltose and maltose in serum sample by high-performance anion-exchange chromatography coupled with integrated pulsed amperometric detection was developed. The four target analytes were easily and completely separated on an anion-exchange column at a flow-rate of 0.25 mL/min by binary step gradient elution in about 16 min and the two eluents were deionized water and 500 mM sodium hydroxide, respectively. The separated four analytes were detected directly by using a gold electrode and quadruple-potential waveform integrated pulsed amperometry without derivatization. Under the optimized conditions, when the injection volume was 25 microL, the detection limits (signal-to-noise ratio equal to 3) for glucose, ribose, isomaltose and maltose were 0.92, 7.50, 12.9 and 10.3 ng/mL, respectively. The calibration graphs of peak area for the four analytes were linear over two to three orders of magnitude with correlation coefficients greater than 0.998. R.S.D. of peak areas of the four analytes for five determinations were no more than 5.6%. The analytical method had been applied to the determination of glucose, ribose, isomaltose and maltose in real serum samples and good results with low relative standard deviation not more than 5.3% were obtained. The accuracy of the proposed method was tested by recovery measurements on spiked samples and good recovery results (98.1-107.9%) were obtained.

Quench-flow analysis reveals multiple phases of GluT1-mediated sugar transport.

Standard models for carrier-mediated nonelectrolyte transport across cell membranes do not explain sugar uptake by human red blood cells. This means that either (1) the models for sugar transport are incorrect or (2) measurements of sugar transport are flawed. Most measurements of red cell sugar transport have been made over intervals of 10 s or greater, a range which may be too long to measure transport accurately. In the present study, we examine the time course of sugar uptake over intervals as short as 5 ms to periods as long as 8 h. Using conditions where transport by a uniform population of cells is expected to be monophasic (use of subsaturating concentrations of a nonmetabolizable but transported sugar, 3-O-methylglucose), our studies demonstrate that red cell sugar uptake is comprised of three sequential, protein-mediated events (rapid, fast, and slow). The rapid phase is more strongly temperature-dependent than the fast and slow phases. All three phases are inhibited by extracellular (maltose or phloretin) or intracellular (cytochalasin B) sugar-transport inhibitors. The rate constant for the rapid phase of uptake is independent of the 3-O-methylglucose concentration. The magnitude (moles of sugar associated with cells) of the rapid phase increases in a saturable manner with [3-O-methylglucose] and is similar to (1) the amount of sugar that is retained by red cell membrane proteins upon addition of cytochalasin B and phloretin and (2) the d-glucose inhibitable cytochalasin B binding capacity of red cell membranes. These results are consistent with the hypothesis that previous studies have both under- and overestimated the rate of erythrocyte sugar transport. These data support a transport mechanism in which newly bound sugars are transiently sequestered within the translocation pathway where they become inaccessible to extra- and intracellular water.

[Effect of a dialysis solution with icodextrin on ultrafiltration and selected metabolic parameters in patients treated with peritoneal dialysis]. / Vliv podání dialyzacního roztoku s icodextrinem na ultrafiltraci a vybrané metabolické parametry nemocných lécených peritoneální dialýzou.

BACKGROUND: To date, peritoneal dialysis has been performed almost exclusively using dialysis solutions containing glucose as the osmotic agent. Use of these solutions is fraught with problems regarding adequate fluid removal from the body and is also associated with undesirable metabolic effects; hence the search for alternative osmotic agents. A dialysis solution with the glucose polymer icodextrin generates ultrafiltration on the principle of colloidal osmosis. The aim of the study was to establish the effect of icodextrin-base dialysis solution on the magnitude of ultrafiltration and evaluate selected metabolic parameters of patients treated by ambulatory peritoneal dialysis. METHODS AND RESULTS: A total of 9 patients whose glucose-based solution was replaced by an icodextrin-based solution during the night-time exchange were evaluated. A control group of 9 patients used glucose-solution during all exchanges. Night-time bag ultrafiltration, blood pressure, and the serum levels of lipids, insulin, leptin, maltose, and amylase were determined before icodextrin administration (time 0), at one-month intervals (time 1, 2, 3), and one month after study completion (time 4). In icodextrin-treated patients, ultrafiltration rose from 246.5 +/- 60.5 ml (mean +/- SEM) at time 0 to 593.1 +/- 87.4 ml; p < 0.01, at time 1, to 547 +/- 67 ml; p < 0.05, at time 2, and to 586.7 +/- 58.8 ml; p < 0.01, at time 3, the icodextrin administration led to a rise in maltose from 0.02 +/- 0.01 g/l at time 0 to 0.1 +/- 0.1 g/l; p < 0.01, at time 1, to 1.0 +/- 0.09 g/l; p < 0.01, at time 2, and to 1.1 +/- 0.09 g/l; p < 0.01, at time 3, with a fall to zero values at time 4 (NS). Icodextrin administration was followed by a decrease in leptinemia from 34.6 +/- 17.2 ng/ml at time 0 to 21.7 +/- 8.9 ng/ml; p < 0.05, at time 1, to 21.4 +/- 9.5 ng/ml; p < 0.05, at time 2, and to 15.9 +/- 24.1 ng/ml; p < 0.05 at time 4. Insulin and lipid levels were not affected. There was no change in the above parameters in the control group. Icodextrin-treated patients reduced their antihypertensive medication, but not statistically significantly. CONCLUSION: Icodextrin administration significantly increase ultrafiltration thus providing for effective control of hydration status without the need for high-level glucose-based dialysis solutions. The use of a glucose polymer-based dialysis solution is associated with a significant yet reversible rise in serum maltose. The decrease in leptin may signal a reduction in body weight after replacing glucose in dialysis solutions with icodextrin, or enhanced rates of leptin elimination as a result of ultrafiltration-induced convective transport.

Clinical experience with icodextrin in children: ultrafiltration profiles and metabolism.

Icodextrin use in adults provides sustained ultrafiltration (UF) in long-term dwells. No information is available on UF and metabolism in children. In 11 children, a volume of 1,049+/-138 ml/m2 of the study fluid (1.36% glucose, 7.5% icodextrin, 3.86% glucose) was administered for 12 h. Net UF with icodextrin (339+/-147 ml/1.73 m2) did not differ from UF with 3.86% glucose (450+/-306 ml/1.73 m2, P=0.53) and was higher than UF with 1.36% glucose (-87+/-239 ml/1.73 m2, P=0.003). Icodextrin added 0.52+/-0.07 to the weekly Kt/V. Over 6 weeks, icodextrin was used for 12-h daytime dwell. Total icodextrin reached a steady-state level of 2.91+/-1.22 g/l at 2 weeks. The main icodextrin metabolites were maltose, maltotriose, and maltotetraose. After 2 weeks, steady state levels were 2.02+/-0.66 mmol/l, 1.46+/-0.35 mmol/l, and 0.45+/-0.12 mmol/l. No icodextrin or metabolites were detectable 4 weeks after the study. We conclude that 7.5% icodextrin is capable of maintaining UF during 12-h dwell in children and is comparable to UF obtained with 3.86% glucose. Steady-state levels of icodextrin and metabolites were reached at 2 weeks and disappeared after the study.

Stop-flow analysis of cooperative interactions between GLUT1 sugar import and export sites.

The human erythrocyte sugar transporter is thought to function either as a simple carrier (sugar import and sugar export sites are presented sequentially) or as a fixed-site carrier (sugar import and sugar export sites are presented simultaneously). The present study examines each hypothesis by analysis of the rapid kinetics of reversible cytochalasin B binding to the sugar export site in the presence and absence of sugars that bind to the sugar import site. Cytochalasin B binding to the purified, human erythrocyte glucose transport protein (GLUT1) induces quenching of GLUT1 intrinsic tryptophan fluorescence. The time-course of GLUT1 fluorescence quenching reflects a second-order process characterized by simple exponential kinetics. The pseudo-first-order rate constant describing fluorescence decay (kobs) increases linearly with [cytochalasin B] while the extent of fluorescence quenching increases in a saturable manner with [cytochalasin B]. Rate constants for cytochalasin B binding to GLUT1 (k1) and dissociation from the GLUT1.cytochalasin B complex (k-1) are obtained from the relationship: kobs = k-1 + k1[cytochalasin B]. Low concentrations of maltose, D-glucose, 3-O-methylglucose, and other GLUT1 import-site reactive sugars increase k-1(app) and reduce k1(app) for cytochalasin B interaction with GLUT1. Higher sugar concentrations decrease k1(app) further. The simple carrier mechanism predicts that k1(app) alone is modulated by import- and export-site reactive sugars and is thus incompatible with these findings. These results are consistent with a fixed-site carrier mechanism in which GLUT1 simultaneously presents cooperative sugar import and export sites.