Isomaltulose Research Articles

Isomaltulose Enhances GLP-1 and PYY Secretion to a Mixed Meal in People With or Without Type 2 Diabetes as Compared to Saccharose.

Secretion of the gut hormones glucagon-like peptide (GLP-1) and peptide YY (PYY) are induced by nutrients reaching the lower small intestine which regulate insulin and glucagon release, inhibit appetite, and may improve β-cell regeneration. The aim is to test the effect of a slowly digested isomaltulose (ISO) compared to the rapidly digested saccharose (SAC) as a snack given 1h before a standardized mixed meal test (MMT) on GLP-1, PYY, glucose-dependent insulinotropic peptide (GIP), and metabolic responses in participants with or without type 2 diabetes (T2DM). Fifteenhealthy volunteers and 15 patients with T2DM consumed either 50g ISO or SAC 1h preload of MMT on nonconsecutive days. Clinical parameters and incretin hormones are measured throughout the whole course of MMT. Administration of 50g ISO as compared to SAC induced a significant increase in GLP-1, GIP, and PYY responses over 2h after intake of a typical lunch in healthy controls. Patients with T2DM showed reduced overall responses of GLP-1 and delayed insulin release compared to controls while ISO significantly enhanced the GIP and almost tripled the PYY response compared to SAC. A snack containing ISO markedly enhances the release of the metabolically advantageous gut hormones PYY and GLP-1 and enhances GIP release in response to a subsequent complex meal.

High-temperature glycosylation of saccharides to modify molecular conformation of egg white protein and its effect on the stability of high internal phase emulsions

This paper investigates the freeze–thaw stability of oil-in-water emulsions stabilized by high-temperature wet heating glycosylation products. Glucose (Glu), D-fructose (Fru), xylose (Xyl), maltodextrin (MD), oligofructose (FO), and oligomeric isomaltulose (IMO) were chosen as sugar sources for the glycosylation reaction with egg white proteins (EWPs) at 120 °C to prepare the GEWPs. The study reveals that the type of sugar significantly influences the Maillard reactions with EWPs. The degree of glycosylation was highest in the Xyl group with the greatest reducing capacity and lowest in the MD, FO, and IMO groups. High-temperature wet glycosylation treatment induced changes in the secondary and tertiary structures of EWP. Elevated temperature exposed hydrophobic groups within the protein, while covalent binding of hydrophilic carbohydrates via the Maillard reaction decreased the protein's H0 value. Improved foaming and emulsifying properties were attributed to the increase in α-helix content, disulfide bond formation, and reduced surface tension. Emulsions prepared from GEWPs exhibited higher apparent viscosity and G' compared to those from natural EWPs, with the GEWP/Xyl group showing the highest values. After freeze–thaw treatment, the GEWP/Fru and GEWP/FO groups demonstrated superior stability and reduced freezing point, along with minimal microstructural alterations. These findings underscore the importance of sugar type in the stability of high internal phase emulsions (HIPEs) stabilized by GEWPs, indicating that a tailored Maillard reaction can yield stabilizers with exceptional freeze–thaw stability for emulsions.

Cryoprotectant Effects on Duck Surimi During Frozen Storage

The surimi-like material made from duck (DSLM) was investigated on the freeze-thaw stability during 4 months of frozen storage using different low-sweetness cryoprotectants such as palatinose (PAL), trehalose (TRE), polydextrose (PLD), maltodextrin (MAL), sucrose and sorbitol (SS), and lactitol (LAC) at a 6% concentration. As compared to the CON, the inclusion of cryoprotectants significantly improved the water-holding capacity of all treated samples. Particularly, as compared to all of the cryoprotectants evaluated, the PLD and PAL samples displayed greater stability concerning Ca2+-ATPase activity, sulfhydryl concentration, and protein solubility. All samples' endothermic peaks declined over time, showing changes in thermal characteristics during storage. A scanning electron microscope (SEM) observation of the CON and LAC-treated samples after 4 months of frozen storage revealed an increase in the number of pores. These findings imply that low-sweetness PLD and PAL outperformed the usual cryoprotectant combination of sucrose and sorbitol (SS) and that they could be used in frozen DSLM. They provide greater water-holding capacity, anti-freezing characteristics, lowered sulfhydryl oxidation, increased protein solubility, and structural integrity, which renders them useful components for innovation in the frozen surimi-like material industry.

Pre-exercise isomaltulose intake affects carbohydrate oxidation reduction during endurance exercise and maximal power output in the subsequent Wingate test

BackgroundIngestion of low-glycemic index (GI) isomaltulose (ISO) not only suppresses subsequent carbohydrate (CHO) oxidation but also inversely retains more CHO after prolonged endurance exercise. Therefore, ISO intake may affect anaerobic power output after prolonged endurance exercise. This study aimed to clarify the time course of CHO utilization during endurance exercise after a single intake of ISO or sucrose (SUC) and the anaerobic power output at the end of endurance exercise.MethodsAfter an intake of either ISO or SUC, 13 athletes were kept at rest for 60 min. Thereafter, they performed a 90-min of treadmill running at their individual target level of % {rm{dot V}}{{rm{O}}_2}max. During the experimental session, the expired gas was recorded, and the energy expenditure (EE) and CHO oxidation rate were estimated. Immediately after 90 min of running, a 30-s Wingate test was performed, and the maximal anaerobic power output was compared between the ISO and SUC conditions.ResultsThe percentage of CHO-derived EE increased rapidly after CHO intake and then decreased gradually throughout the experiment. The slopes of the regression lines calculated from the time course in the CHO-derived EE were significantly (negatively) larger in the SUC condition (-19.4 ± 9.6 [%/h]) than in the ISO condition (-13.3 ± 7.5 [%/h]). Furthermore, the maximal power output in the Wingate test immediately after the endurance exercise was significantly higher in the ISO condition than in the SUC condition (peak power: 12.0 ± 0.6 vs. 11.5 ± 0.9 [W/kg]).ConclusionCompared with SUC intake, ISO intake does not produce an abrupt decline in the percentage of CHO-derived EE during prolonged endurance exercise; it remains relatively high until the final exercise phase. Additionally, anaerobic power output at the end of the exercise, largely contributed by anaerobic glycolysis, was greater after ISO intake than after SUC intake.

Lidocaine hydrochloride loaded isomaltulose microneedles for efficient local anesthesia of the skin

Lidocaine hydrochloride (LIDH) as an anesthetic is widely used in local anesthesia. Dissolving microneedles (MNs) have great application value in the field of skin anesthesia. However, the limited drug-loading of dissolving MNs is an existing challenge that affects clinical use. In this study, we have screened isomaltulose (ISO) as the proper matrix material for the MNs by using molecular dynamics (MD) simulation. Our findings indicate that ISO has good compatibility with LIDH, and the LIDH-loaded ISO MNs (LI-MNs) have high drug-loading capacity. The drug-loading capacity of LI-MNs could reach 80%, and it could effectively puncture the skin. In addition, the preparation method of customized LI-MNs was established based on three-dimensional (3D) printing technology. It was shown that the administration time of LI-MNs could be controlled within 3 min. Also, the LI-MNs were able to provide the local anesthetic efficacy within 2 min and sustained for more than 2 h. Significantly, LI-MNs had more efficient drug efficacy compared to the topical creams and the majority of existing LIDH-loaded dissolving MNs. They even provided a longer duration of action than the injections. Overall, the LI-MNs with high drug-loading have a promising application prospect.

Implication of sugar, protein and incretins in excessive glucagon secretion in type 2 diabetes after mixed meals

Amino acids powerfully release glucagon but their contribution to postprandial hyperglucagonemia in type 2 diabetes remains unclear. Exogenously applied GIP stimulates, while GLP-1 inhibits, glucagon secretion in humans. However, their role in mixed meals is unclear, which we therefore characterized. In three experiments, participants with type 2 diabetes and obese controls randomly received different loads of sugars and/or proteins. In the first experiment, participants ingested the rapidly cleaved saccharose (SAC) or slowly cleaved isomaltulose (ISO) which is known to elicit opposite profiles of GIP and GLP-1 secretion. In the second one participants received test meals which contained saccharose or isomaltulose in combination with milk protein. The third set of participants underwent randomized oral protein tests with whey protein or casein. Incretins, glucagon, C-peptide, and insulin were profiled by specific immunological assays. 50g of the sugars alone suppressed glucagon in controls but slightly less in type 2 diabetes patients. Participants with type 2 diabetes showed excessive glucagon responses within 15min and lasting over 3h, while the obese controls showed small initial and delayed greater glucagon responses to mixed meals. The release of GIP was significantly faster and greater with SAC compared to ISO, while GLP-1 showed an inverse pattern. The glucagon responses to whey or casein were only moderately increased in type 2 diabetes patients without a left shift of the dose response curve. The rapid hypersecretion of glucagon after mixed meals in type 2 diabetes patients compared to controls is unaffected by endogenous incretins. The defective suppression of glucagon by glucose combined with hypersecretion to protein is required for the exaggerated response. NCT03806920, NCT02219295, NCT04564391.

Enhancement of healthful novel sugar contents in genetically engineered sugarcane juice integrated with molecularly characterized ThSyGII (CEMB-SIG2)

Enhancement of sugar contents and yielding healthful sugar products from sugarcane demand high profile scientific strategies. Previous efforts to foster manipulation in metabolic pathways or triggering sugar production through combating abiotic stresses fail to yield high sugar recovery in Saccharum officinarum L. Novel sucrose isomers trehalulose (TH) and isomaltulose (IM) are naturally manufactured in microbial sources. In pursuance of novel scientific methodology, codon optimized sucrose isomerase gene, Trehalulose synthase gene II(CEMB-SIG2) cloned under dual combined stem specific constitutive promoters in pCAMBIA1301 expression vector integrated with Vacuole targeted signal peptide (VTS) to concentrate gene product into the vacuole. The resultant mRNA expression obtained by Real Time PCR validated extremely increased transgene expression in sugarcane culms than leaf tissues. Overall sugar estimation from transgenic sugarcane lines was executed through refractometer. HPLC based quantifications of Trehalulose (TH) alongside different internodes of transgenic sugarcane confirmed the enhancement of boosted sugar concentrations in mature sugarcane culms. Trehalulose synthase gene II receptive sugarcane lines indicated the unprecedented impressions of duly combined constitutive stem regulated promoters. Transgenic sugarcane lines produce highest sugar recovery percentages, 14.9% as compared to control lines (8.5%). The increased sugar recovery percentage in transgenic sugarcane validated the utmost performance and expression of ThSyGII gene .High Profile Liquid chromatography based sugar contents estimation of Trehalulose (TH) and Isomaltulose (IM) yielded unprecedented improvement in the whole sugar recovery percentage as compared to control lines.⁠

Incorporation and influence of natural gums in an alginate matrix for Serratia plymuthica immobilization and isomaltulose production

Isomaltulose (IM) is a non-cariogenic sugar and substitute for sucrose that has been widely used in candies and soft drinks. This sugar is obtained from sucrose through enzymatic conversion, catalyzed by microbial glucosyltransferases. In this study, alternative gums, namely: gum Arabic (GA), algaroba gum (AG), and cashew gum (CG) were combined with alginate (ALG) for the immobilization of Serratia plymuthica, with the aim of improving its capability for conversion of sucrose into IM. Prior to the immobilization, the gums were characterized using FTIR spectroscopy, TGA, and XRD analysis. Then, they were combined with ALG and used to immobilize a cell mass of S. plymuthica by ionic gelation. The morphology of the produced beads was visualized using SEM, and the sucrose into IM conversion using the beads was performed in batch and continuous processes. CG showed the highest thermal stability and crystallinity. The use of CG (2.0 %, w/v) combined with ALG (2.0 %, w/v) showed the highest value for isomaltulose (236.46 g/L) produced in the first batch, and high stability in the continuous conversion process; resulting in an IM production of 199.24 g/L at 72 h of reaction. In addition, this combination produced less porous beads, able to maintain the entrapped cells longer. In conclusion, the production of IM by Serratia plymuthica cells immobilized in a matrix composed of ALG and CG is recommended, due to its high conversion capacity and high stability.

Effects of ingestion of isomaltulose beverage on plasma volume and thermoregulatory responses during exercise in the heat.

Isomaltulose is a low glycemic and insulinaemic carbohydrate increasingly used as an alternative sweetener in commercial beverages. While isomaltulose beverages can improve hydration status compared to sucrose-based beverages, it remains unclear if ingestion of an isomaltulose beverage prior to exercise in the heat may improve plasma volume (PV) and thermoregulatory responses. Twelve endurance-trained men consumed a 1L carbohydrate beverage containing either 6.5%-sucrose (SUC) or 6.5%-isomaltulose (ISO) 60min prior to 5 successive, 15-min bouts of moderate-intensity (60% of their pre-determined maximum oxygen uptake) in the heat (32°C, 50% relative humidity), each separated by a 5min rest. A 6th bout was performed, wherein the participant adjusted running speed to maximize distance covered within the 15-min period. The change (Δ) in PV, heart rate (HR), body core (rectal and gastrointestinal) and skin temperatures, and whole-body sweat loss were assessed during each exercise bout. Ingestion of ISO induced a higher ΔPV at 4th bout only (P < 0.001) and lower HR (P = 0.032, main effect of beverage) during exercise compared to those of SUC. Body core and skin temperatures and whole-body sweat loss did not differ between conditions (all P ≥ 0.192, interaction effect). Running distance covered in final exercise bout tended to increase (~ 5%) in ISO versus SUC (P = 0.057, d = 0.64). Relative to a sucrose-based beverage, ISO ingestion prior to exercise in the heat reduced cardiovascular strain by preserving PV and attenuating HR, albeit with no corresponding benefit on thermoregulatory function. The former response may facilitate improvements in exercise performance.

Influence of Isomaltulose Ingestion on Fat Oxidation During Inclemental Exercise in Endurance Athletes

Isomaltulose (ISO) is a carbohydrate (CHO) with metabolic properties that makes it slowly digested and less likely to raise postprandial blood glucose response. We considered that isomaltulose ingestion was difficult to inhibit fat oxidation during incremental exercise. Here we investigated the effect of isomaltulose ingestion on fat oxidation during incremental exercise on a cycle ergometer in endurance athletes (n=10) who performed an incremental exercise after ISO or sucrose (SUC) ingestion. We measured the fat and CHO oxidation, blood glucose concentration, and blood lactate concentration of the subjects during the incremental exercise. Between the ISO and SUC groups, the fat oxidation was significantly different at 3 min (p<0.05) and CHO oxidation was significantly different at 3, 6, and 12 min (p<0.05). The ISO group's blood glucose concentrations were significantly lower than those of the SUC group at −5, 3, 6, 9, and 12 min (p<0.05). Similarly, the ISO group's blood lactate concentrations were significantly lower than those of the SUC group at −5, 0, 3, 6, 9, and 18 min (p<0.05). These results indicate that isomaltulose ingestion causes only slight fat oxidation inhibition and a slow increase in blood lactate levels compared with sucrose ingestion by a gradual rise in the blood glucose level.

Mature‐stem expression of a silencing‐resistant sucrose isomerase gene drives isomaltulose accumulation to high levels in sugarcane

Isomaltulose (IM) is a natural isomer of sucrose. It is widely approved as a food with properties including slower digestion, lower glycaemic index and low cariogenicity, which can benefit consumers. Availability is currently limited by the cost of fermentative conversion from sucrose. Transgenic sugarcane plants with developmentally-controlled expression of a silencing-resistant gene encoding a vacuole-targeted IM synthase were tested under field conditions typical of commercial sugarcane cultivation. High yields of IM were obtained, up to 483mm or 81% of total sugars in whole-cane juice from plants aged 13months. Using promoters from sugarcane to drive expression preferentially in the sugarcane stem, IM levels were consistent between stalks and stools within a transgenic line and across consecutive vegetative field generations of tested high-isomer lines. Germination and early growth of plants from setts were unaffected by IM accumulation, up to the tested level around 500mm in flanking stem internodes. These are the highest yields ever achieved of value-added materials through plant metabolic engineering. The sugarcane stem promoters are promising for strategies to achieve even higher IM levels and for other applications in sugarcane molecular improvement. Silencing-resistant transgenes are critical to deliver the potential of these promoters in practical sugarcane improvement. At the IM levels now achieved in field-grown sugarcane, direct production of IM in plants is feasible at a cost approaching that of sucrose, which should make the benefits of IM affordable on a much wider scale.

A double blind clinical trial evaluating the relative pharmacokinetics and bioavailability of oral creatine monohydrate when combined with either isomaltulose or dextrose in healthy adult males

Methods In a prospective, randomized, double blind, active-comparator-controlled, parallel group pilot study, 30 male subjects, age 27.0 ± 4.6 years, with BMI of 24.75 ± 1.99 kg/m and a body surface area (BSA) of 1.953 ± 00.75 m, were randomly assigned to ingest 3 grams of creatine monohydrate (CM) in combination with isomaltulose (ISO) or dextrose (DEX) in 1 of 3 concentrations (5 gm liquid, 17 gm capsules or 50 gm liquid). Rate of absorption (tMax) and overall absorption (from BSA adjusted AUC0-8h and CMax) of CM was determined via changes in serum creatine over an 8-hour test period. Blood was collected at baseline and 0.5, 1, 2.5, 4 and 8 hours post ingestion with efficacy endpoints including CMax, tMax, AUC0-8h and lElim derived from normalized concentration vs. time curves for serum creatine (AUC by trapezoidal integration). Serum creatine levels were normalized by BSA using the Mosteller formula. For PK parameters, paired Student t test (or Wilcoxon if nonnormally distributed) was used and for categorical variables, Fisher Exact test (or Chi-Square if necessary) was used. Statistics were calculated by R v2.14.0 (www.r-project.org).

Combining protein and carbohydrate increases postprandial insulin levels but does not improve glucose response in patients with type 2 diabetes

ObjectiveA combined load of carbohydrate and protein stimulates insulin secretion. However, results on postprandial glucose responses in type 2 diabetic (T2D) subjects have been inconclusive. Therefore, we investigated the effects of co-ingestion of carbohydrate and protein on glucose and insulin responses in these subjects. MethodsAfter an overnight fast, 30 subjects consumed a drink containing 50g of slowly-digested isomaltulose (ISO), combined either with a mixture of 21g whey/soy (ISO+WS) or with 21g casein (ISO+C) in a randomized order on separate days. In another experiment, the subjects consumed a control drink containing only 50g ISO. ResultsNo significant differences in glucose responses were observed after ingestion of the drinks. Compared to ingestion of ISO alone, insulin response was ~190%–270% higher (P<.001), whereas insulin action was lower (P<.01) after ingestion of ISO+WS and ISO+C. Plasma insulin levels increased more significantly (P<.001) after ingestion of ISO+WS compared to ISO+C and were positively correlated with total amino acid levels (P<.001). Insulin action, however, showed a greater decrease following ingestion of ISO+WS than ISO+C (P<.01). ConclusionsCombining carbohydrate with protein can elevate postprandial insulin levels, but decreases insulin action, and therefore does not improve glucose response in T2D subjects. Our results further suggest that different types of proteins (i.e., fast-absorbing whey/soy vs. slow-absorbing casein) differently modulate insulin response and insulin action. A fast-absorbing protein mixture reduces insulin action to a greater extent than a slow-absorbing protein, and therefore may not be recommended for glycemic control in T2D patients.

Reduced glycaemic and insulinaemic responses following trehalose and isomaltulose ingestion: implications for postprandial substrate use in impaired glucose-tolerant subjects

The impact of slowly digestible sugars in reducing the risk of developing obesity and related metabolic disorders remains unclear. We hypothesised that such carbohydrates (CHO), resulting in a lower glycaemic and insulinaemic response, may lead to greater postprandial fat oxidation rates in subjects with impaired glucose tolerance (IGT). The present study intends to compare the postprandial metabolic responses to the ingestion of glucose (GLUC) v. trehalose (TRE) and sucrose (SUC) v. isomaltulose (IMU). In a randomised, single-blind, cross-over design, ten overweight IGT subjects were studied four times, following ingestion of different CHO drinks either at breakfast or in combination with a mixed meal at lunch. Before and 3 h after CHO ingestion, energy expenditure, substrate utilisation and circulating metabolite concentrations were determined. Ingestion of CHO drinks with a meal resulted in an attenuated rise in GLUC (-33 %) and insulin (-14 %) concentrations following TRE when compared with GLUC and following IMU, an attenuation of 43 and 34 % when compared with SUC ingestion, respectively. Additionally, there was less inhibition of the rise in NEFA concentrations and less decline in postprandial fat oxidation (22 %) after IMU when compared with SUC, whereas TRE did not differ from GLUC. The attenuated rise in GLUC and insulin concentrations following IMU ingestion attenuated the postprandial inhibition of fat oxidation compared with SUC when co-ingested with a meal. This suggests that exchange of SUC in the diet for IMU may result in a more favourable metabolic response and may help to reduce the risks associated with obesity and type 2 diabetes.

Field performance of transgenic sugarcane expressing isomaltulose synthase

Transgenic sugarcane plants expressing a vacuole-targeted isomaltulose (IM) synthase in seven recipient genotypes (elite cultivars) were evaluated over 3 years at a field site typical of commercial cane growing conditions in the Burdekin district of Australia. IM concentration typically increased with internode maturity and comprised up to 217 mm (33% of total sugars) in whole-cane juice. There was generally a comparable decrease in sucrose concentration, with no overall decrease in total sugars. Sugarcane is vegetatively propagated from stem cuttings known as setts. Culture-derived plants were slower to establish and generally gave shorter and thinner stalks at harvest than those grown from field-sourced setts in the initial field generations. However, after several cycles of field propagation, selections were obtained with cane yields similar to the recipient genotypes. There was no apparent adverse effect of IM accumulation on vigour assessed by stalk height and diameter or other visual indicators including germination of setts and establishment of stools. There was some inconsistency in IM levels in juice, between samplings of the vegetatively propagated transgenic lines. Until the causes are resolved, it is prudent to selectively propagate from stalks with higher IM levels in the initial vegetative field generations. Pol/Brix ratio allowed rapid identification of lines with high IM levels, using common sugar industry instruments. Sucrose isomerase activity was low in these transgenic lines, and the results indicate strong potential to develop sugarcane for commercial-scale production of IM if higher activity can be engineered in appropriate developmental patterns.

Exogenous Oxidation of Isomaltulose Is Lower than That of Sucrose during Exercise in Men

Isomaltulose (ISO) is a disaccharide that is slowly digested, resulting in a slow availability for absorption. The aim of this study was to compare the blood substrate responses and exogenous carbohydrate (CHO) oxidation rates from orally ingested sucrose (SUC) and ISO during moderate intensity exercise. We hypothesized that the oxidation of ISO is lower compared with SUC, resulting in lower plasma glucose and insulin concentrations and subsequent lower CHO and higher fat oxidation rates. Ten trained men [maximal oxygen uptake (VO2max), 64 ± 1 mL/(kg body mass·min)] cycled on 3 occasions for 150 min at 59 ± 2% VO2max and consumed either water (WAT) or 1 of 2 CHO solutions providing 1.1 g/min of CHO in the form of either SUC or ISO. Peak exogenous CHO oxidation rates were higher (P < 0.05) during the SUC trial (0.92 ± 0.03 g/min) than during the ISO trial (0.54 ± 0.05 g/min). Total endogenous CHO oxidation over the final 90 min of exercise was lower (P < 0.05) in the SUC trial (107 ± 10 g) than in the WAT (137 ± 7 g) and ISO (127 ± 9 g) trials. Fat oxidation was higher during the WAT trial than during the SUC and ISO trials. ISO resulted in a lower plasma insulin response at 30 min compared with SUC, whereas the glucose response did not differ between the 2 CHO. Oxidation of ingested ISO was significantly less than that of SUC, most likely due to the lower rate of digestion of ISO. A lower CHO delivery and a small difference in plasma insulin may have resulted in higher endogenous CHO use and higher fat oxidation during the ISO trial than during the SUC trial.

Sugar transport across the plasma membrane of leaf cells: from physiology to transgenesis

Sugars made by photosynthesis must cross several cells before being loaded into the phloem. The first part of the paper will review the data available on the physiology, biochemistry and molecular biology of sucrose and hexose transport across the plasma membrane of the different leaf cells. The second part will describe data involving transgenesis with sugar transporters cDNAs or promoters. Among these, a detailed study on transgenic tobacco plants modified on hexose transport will be reported. Tobacco plants were transformed with a chimeric construct containing the VvHT1 cDNA (putative hexose transporter expressed in young leaves and berries of grapevine) under the CaMV 35S promoter. About 20 sense plants and 10 anti-sense plants were obtained and cultured in vitro. Two sense plants present a very marked phenotype, due to a smaller leaf size and a poor development of the roots. This is likely due to the strong homology existing between VvHT1, and NtMST1, the endogenous hexose transporter from tobacco, which may indirectly induce a general repression of hexose transport activity. Glucose uptake was reduced in leaf discs from these plants. The phenotype can be suppressed by the addition of high glucose concentrations into the culture media, suggesting a relationship between hexose availability and plant size. The activity of the VvHT1 promoter was also studied with reporter genes. In transgenic tobacco plants, GUS activity was much higher in young leaves than in source leaves. In tobacco BY2 cells, the promoter activity was stimulated by sucrose, glucose, and palatinose, but not by fructose.

The effect of pH and oxygen concentration on the formation of 3-ketodisaccharides by Agrobacterium tumefaciens.

The further optimization of 3-ketodisaccharide formation with sucrose, leucrose and iso maltulose was studied with special regard to pH and oxygen concentration in the reaction mixture with resting cells of Agrobacterium tumefaciens. It was found that the optimal pH values for the highest reaction rate and highest yield were different as the pH affected the stability of the 3-keto derivatives formed. A pH shift to 5.0 clearly reduced the enzymatic degradation of the 3-keto derivatives thus stabilizing them. The influence of constant oxygen concentrations on 3-ketosucrose formation was tested showing results not explicable with normal Michaelis-Menten kinetics. For each substrate a maximum of reaction rate and yield were obtained at very low oxygen concentrations.