Regulation and butanol inhibition of D-xylose and D-glucose uptake in Clostridium acetobutylicum.

Clostridium acetobutylicum exhibited diauxie growth in the presence of mixtures of glucose and xylose. Both glucose- and xylose-grown cells had a glucose uptake activity. On the other hand, growth on xylose was associated with the induction of a xylose permease activity, which was repressed by glucose in xylose-induced cells. The rate of sugar uptake with increasing sugar concentrations showed saturation kinetics with an apparent Km of 1.25 X 10(-5) M for glucose and 5 X 10(-3) M for xylose. Concomitant with the production of solvents, the activities of the glucose and xylose transport systems decreased. Among the main products of fermentation, butanol was shown to be a potent inhibitor of the growth of the organism and of the rate of sugar uptake as well as of sugar incorporation into cell materials. These inhibitory effects of butanol were more pronounced in xylose-grown cells than in glucose-grown cells. Butanol completely inhibited growth at a concentration of 14 g/liter for cultures growing on glucose and 8 g/liter for cultures growing on xylose. Concentrations of 7 and 10.5 g/liter of butanol caused a 50% inhibition of the xylose and glucose incorporations into cell materials. These inhibitory levels of butanol were found in typical glucose or xylose fermentation.     

Regulation and butanol inhibition of D-xylose and D-glucose uptake in Clostridium acetobutylicum

Clostridium acetobutylicum exhibited diauxie growth in the presence of mixtures of glucose and xylose. Both glucose- and xylose-grown cells had a glucose uptake activity. On the other hand, growth on xylose was associated with the induction of a xylose permease activity, which was repressed by glucose in xylose-induced cells. The rate of sugar uptake with increasing sugar concentrations showed saturation kinetics with an apparent Km of 1.25 X 10(-5) M for glucose and 5 X 10(-3) M for xylose. Concomitant with the production of solvents, the activities of the glucose and xylose transport systems decreased. Among the main products of fermentation, butanol was shown to be a potent inhibitor of the growth of the organism and of the rate of sugar uptake as well as of sugar incorporation into cell materials. These inhibitory effects of butanol were more pronounced in xylose-grown cells than in glucose-grown cells. Butanol completely inhibited growth at a concentration of 14 g/liter for cultures growing on glucose and 8 g/liter for cultures growing on xylose. Concentrations of 7 and 10.5 g/liter of butanol caused a 50% inhibition of the xylose and glucose incorporations into cell materials. These inhibitory levels of butanol were found in typical glucose or xylose fermentation.     

Fructose transport in Neurospora crassa.

A specific fructose uptake system (Km = 0.4 mM) appeared in Neurospora crassa when glucose-grown mycelia were starved. Fructose uptake had kinetics different from those of intramycelial fructose phosphorylation, and uptake appeared to be carrier mediated. The only sugar which competitively inhibited fructose uptake was L-sorbose (Ki = 9 mM). Glucose, 2-deoxyglucose, mannose, and 3-O-methyl glucose were noncompetitive inhibitors of fructose uptake. Incubation of glucose-grown mycelia with glucose, 2-deoxyglucose, or mannose prevented derepression of the fructose transport system, whereas incubation with 3-O-methyl glucose caused the appearance of five times as much fructose uptake activity as did starvation conditions.     

Characterization and regulation of galactose transport in Neurospora crassa

Two galactose uptake systems were found in the mycelia of Neurospora crassa. In glucose-grown mycelia, galactose was transported by a low-affinity (Km = 400 mM) constitutive system which was distinct from the previously described glucose transport system I (R. P. Schneider and W. R. Wiley, J. Bacteriol. 106:479--486, 1971). In carbon-starved mycelia or mycelia incubated with galactose, a second galactose transport activity appeared which required energy, had a high affinity for galactose (Km = 0.7 mM), and was shown to be the same as glucose transport system II. System II also transported mannose, 2-deoxyglucose, xylose, and talose and is therefore a general monosaccharide transport system. System II was derepressed by carbon starvation, completely repressed by glucose, mannose, and 2-deoxyglucose, and partially repressed by fructose and xylose. Incubation with galactose yielded twice as much activity as starvation. This extra induction by galactose required protein synthesis, and represented an increase in activity of system II rather than the induction of another transport system. Glucose, mannose, and 2-deoxyglucose caused rapid degradation of preexisting system II; fructose and xylose caused a slower degradation of activity.     

The Effect of Nonanal on Dipodascus aggregatus IV. Studies with Different Carbon Sources

Nonanal (80 μ) in ethanolic solution stimulated the growth of Dipodascus aggregatus with fructose (55.5 mM) as carbon source (inoculum grown with fructose or glucose). If the inoculum had been grown with galactose, neither growth with galactose nor growth with glucose was affected by nonanal. If the inoculum had been grown with glucose, growth with galactose was weakly. stimulated. —Growth with galactose (galactose-grown inoculum) was strongly stimulated by nonanal if xylose at a low concentration (0.53 mM) was added. — The oxygen uptake of glucose grown cells with glucose as substrate was stimulated by 200 μM nonanal in the absence of ethanol. The respiratory activity of galactose-grown cells was also stimulated with galactose as well as with glucose as substrate. In the absence of exogenous substrate the oxygen uptake of glucose-grown cells was weakly stimulated by nonanal whereas that of galactose-grown cells was strongly stimulated.     

Purine nucleotide reutilization by human lymphoblast lines with aberrations of the inosinate cycle

A purine nucleotide (inosinate) cycle is demonstrated with human lymphoblasts. The lymphoblast requires approximately 50 nmol of purine/10(6) cell increment. When the inosinate cycle is interrupted by the genetic, severe deficiency of either or both purine nucleoside phosphorylase (PNP) or hypoxanthine phosphoribosyltransferase (HPRT), purine accumulates in the culture medium as inosine, guanosine, deoxyinosine, and deoxyguanosine (PNP deficiency or PNP, HPRT deficiency) or hypoxanthine and guanine (HPRT deficiency). This accumulation represents an additional 25 to 32 nmol of purine which must be synthesized per 10(6) cell increment. PNP-deficient lymphoblasts have PPRibP contents characteristic of normal lymphoblasts, about 20 to 25 pmol/10(6) cells. HPRT-deficient lymphoblasts have four times higher PPRibP contents. The lymphoblast deficient for both PNP and HPRT has only a marginal elevation of PPRibP content, 1.5 times normal values. The elevated PPRibP content of HPRT-deficient cells reflects the efficient, unilateral reutilization of the ribose moiety of purine ribonucleotides and is not a cause of purine overproduction. Purine overproduction characterizing PNP-deficient lymphoblasts appears similar to overproduction from deficiency of HPRT, i.e. a break in the inosinate cycle rather than overactive de novo purine synthesis.     

Superactivity of human phosphoribosyl pyrophosphate synthetase due to altered regulation by nucleotide inhibitors and inorganic phosphate

Phosphoribosyl pyrophosphate (PPRibP) synthetase activity was studied in cultured fibroblasts and lymphoblasts from a male child (patient 2-A) in whom inherited purine nucleotide and uric acid overproduction are accompanied by neurological deficits. Chromatographed or partially purified preparations of the child's enzyme showed 5-6-fold increased inhibitory constants (I0.5) for the noncompetitive inhibitors GDP and 6-methylthioinosine monophosphate but normal responsiveness to the competitive inhibitors ADP and 2,3-diphosphoglycerate. Activation of the PPRibP synthetase of patient 2-A by Pi was also abnormal with 3-4-fold reduced apparent KD values for Pi. Superactivity of the PPRibP synthetase of this child thus appeared to result from a combination of regulatory defects; selective resistance to noncompetitive inhibitors and increased responsiveness to Pi activation. Selective growth of the patient's fibroblasts in medium containing 6-methylthioinosine confirmed the functional significance of the in vitro inhibitor resistance of the aberrant enzyme. Fibroblasts and lymphoblasts derived from patient 2-A showed increased concentrations and rates of generation of PPRibP as well as increased rates of the pathways of purine base salvage and purine nucleotide synthesis de novo. The magnitudes of these increases in the child's cells exceeded those in cells with catalytically superactive PPRibP synthetases. These alterations as well as the in vitro kinetic abnormalities in the patient 2-A enzyme were expressed to a reduced degree in fibroblasts from the child's affected mother, supporting the proposal that this woman is a heterozygous carrier for X-linked enzyme superactivity.     

The influence of ATP on sugar uptake mediated by the constitutive glucose carrier of Saccharomyces cerevisiae

The glucose carrier of Saccharomyces cerevisiae transports the phosphorylatable sugars glucose, mannose, fructose and 2-deoxy-D-glucose (2-dGlc) and the non-phosphorylatable sugar 6-deoxy-D-glucose (6-dGlc). Reduction of the ATP concentration by, for example, incubating cells with antimycin A, results in a decrease in uptake of 2-dGlc and fructose. These uptake velocities can be increased again by raising the ATP level. These results establish a role of ATP in sugar transport. Transport of glucose and mannose is less affected by changes in the ATP concentration than 2-dGlc and fructose uptake, while the 6-dGlc transport is independent of the amount of ATP in the cells. Also, reduction of the kinase activity by incubation with xylose diminished transport of 2-dGlc and fructose, while the uptake of glucose and mannose remained unchanged. It is discussed that these results are due to transport-associated phosphorylation with ATP as substrate and the hexokinases and the glucokinase as phosphorylating enzymes.     

Effect of nutrient variations on growth and brefeldin A formation inCurvularia lunata

The highest level of secreted brefeldin A was present in glucose-grown cultures, intermediate levels in glucose-fructose, and xylose cultures and low levels in fructose- and galaotose-grown cultures ofCurvularia lunata. The biomass decreased from glucose, fructose, xylose, glucose-fructose to galactose cultures. Brefeldin A levels and mycelial yields were low in citrate-, gluconate-, and succinate-grown cultures. Inorganic phosphate-limited cultures supported a high level of brefeldin A. Intermediate levels were present in trace elements-, and inorganic phosphate-trace elements-limited cultures.     

Expression of a novel high-affinity purine nucleobase transport function in mutant mammalian T lymphoblasts.

The single nucleoside transport function of mouse S49 lymphoblasts also transports purine bases (B. Aronow and B. Ullman, J. Biol. Chem. 261:2014-2019, 1986). This transport of purine bases by S49 cells is sensitive to inhibition by dipyridamole (DPA) and 4-nitrobenzylthioinosine, two potent inhibitors of nucleoside transport. Therefore, wild-type S49 cells cannot salvage low hypoxanthine concentrations in the presence of 10 microM DPA and 11 microM azaserine; the latter is a potent inhibitor of purine biosynthesis. Among a mutagenized wild-type population, a cell line, JPA2, was isolated which could proliferate in 50 microM hypoxanthine-11 microM azaserine-10 microM DPA. The basis for the survival of JPA2 cells under these selective conditions was expression of a unique, high-affinity purine nucleobase transport function not present in wild-type cells. JPA2 cells could transport 5 microM concentrations of hypoxanthine, guanine, and adenine 15- to 30-fold more efficiently than parental cells did. Kinetic analyses revealed that the affinity of the JPA2 transporter for all three purine bases was much greater than that of the wild-type nucleobase transport system. Moreover, nucleobase transport in JPA2 cells, unlike that in parental cells, was insensitive to inhibition by DPA, 4-nitrobenzylthioinosine, sulfhydryl reagents, and nucleosides. No alterations in nucleoside transport capability, phosphoribosylpyrophosphate levels, or purine phosphoribosyltransferase enzymes were detected in JPA2 cells. Thus, JPA2 cells express a novel nucleobase transport capability which can be distinguished from the nucleoside transport function by multiple biochemical parameters.     

Role of D-ribose as a cometabolite in D-xylose metabolism by Saccharomyces cerevisiae.

The influence of D-ribose as a cosubstrate on the uptake and metabolism of the non-growth substrate D-xylose by Saccharomyces cerevisiae ATCC 26602 was investigated. Xylose was taken up by means of low- and high-affinity glucose transport systems. In cells exposed for 2 days to a mixture of xylose and ribose, only the high-affinity system could be detected. Glucose strongly inhibited the transport of xylose by both systems. Starvation or exposure to either xylose or ribose resulted in inactivation of xylose transport, which did not occur in the presence of a mixture of ribose and xylose. A constitutive non-glucose-repressible NADPH2-dependent xylose reductase with a specific activity of ca. 5 mU/mg of protein that converted xylose to xylitol was present in a glucose-grown culture. No activity converting xylitol to xylulose or vice versa was found in crude extracts. Both xylose and ribose were converted to their corresponding polyols, xylitol and ribitol, as indicated by 13C nuclear magnetic resonance spectroscopy. Furthermore, ethanol was detected, and this implied that pathways for the complete catabolism of xylose and ribose exist. However, the NADPH2 required for the conversion of xylose to xylitol is apparently not supplied by the pentose phosphate pathway since the ethanol produced from D-[1-13C]xylose was labelled only in the C-2 position. Acetic acid was produced from ribose and may assist in the conversion of xylose to xylitol by cycling NADPH2.     

Two glucose transport systems in Bacillus licheniformis.

Bacillus licheniformis NCIB 6346 showed active accumulation of glucose which was inhibited by agents which affect the transmembrane proton gradient. Phosphotransferase (PTS) activity, identified as phosphoenolpyruvate-dependent phosphorylation of glucose, was found in cell extracts but could not be demonstrated in cells permeabilized with toluene when assays were conducted at pH 6.6. The same was true for mannitol and fructose phosphotransferase activities. Cells grown on fructose accumulated glucose at a slower rate than glucose-grown cells, and extracts prepared from them did not contain glucose PTS activity. Examination of the effects of analogs on glucose uptake and phosphorylation showed that 2-deoxyglucose was not a PTS substrate, but did markedly inhibit glucose uptake, with stronger inhibition in cells grown on fructose. Glucose accumulation by whole cells grown on glucose became less sensitive to the uncoupler tetrachlorosalicylanilide (TCS) as the pH was raised from 6.6 to 8.0, while in fructose-grown cells TCS was equally effective across this pH range. PTS activity was exhibited by toluene-treated cells at pH 7.5 and above, although the system itself in extracts was not affected by pH in the range of 5.0 to 8.0. The results are consistent with the presence of two glucose transport systems, one a PTS and the other operating by an alternative mechanisms, and suggest that the PTS in B. licheniformis may be regulated in a pH-dependent manner.     

Purine nucleobase transport in human erythrocytes. Reinvestigation with a novel "inhibitor-stop" assay

A novel "inhibitor-stop" method for the determination of initial rates of purine nucleobase transport in human erythrocytes has been developed, based on the addition of seven assay volumes of cold 19 mM papaverine to terminate influx. In view of our finding that the initial velocities of adenine, guanine, and hypoxanthine influx into human erythrocytes were linear for only 4-6 s at 37 degrees C, the present method has been used to reexamine the kinetics of purine nucleobase transport in these cells. Initial influx rates of all three purine nucleobases were shown to be the result of concurrent facilitated and nonfacilitated diffusion. The nonfacilitated influx rates could be estimated either from the linear concentration dependence of nucleobase influx at high concentrations of permeant or from residual influx rates which were not inhibited by the presence of co-permeants. Appropriate corrections for nonfacilitated diffusion were made to the influx rates observed at low nucleobase concentrations. Kinetic analyses indicated that adenine (Km = 13 +/- 1 microM, n = 7), guanine (Km = 37 +/- 2 microM, n = 5), and hypoxanthine (Km = 180 +/- 12 microM, n = 6) were mutually competitive substrates for transport. The Ki values obtained with each nucleobase as an inhibitor of the influx of the other nucleobases were similar to their respective Km values for influx. Furthermore, the transport of the purine nucleobases was not inhibited by nucleosides (uridine, inosine) or by inhibitors of nucleoside transport (6-[(4-nitrobenzyl)thio]-9-beta-D-ribofuranosylpurine, dilazep, dipyridamole). It is concluded that all three purine nucleobases share a common facilitated transport system in human erythrocytes which is functionally distinct from the nucleoside transporter.     

Phosphoribosyl pyrophosphate and phosphoribosyl pyrophosphate synthetase in rat mammary gland. Changes in the lactation cycle and effects of diabetes, insulin and phenazine methosulphate.

Changes in the tissue content of phosphoribosyl pyrophosphate (PPRibP), glucose 6-phosphate, ribose 5-phosphate (Rib5P), RNA and DNA, of the activity of PPRibP synthetase (EC 2.7.6.1) and the conversion of [1-14C]- and [6-14C]-glucose into 14CO2 were measured at mid-lactation in the normal and diabetic rat and in pregnancy, lactation and mammary involution in the normal rat. The PPRibP, glucose 6-phosphate and Rib5P contents increase during pregnancy and early lactation to reach a plateau value at mid-lactation, before falling sharply during weaning. The PPRibP content, PPRibP synthetase activity and flux of glucose through the oxidative pentose phosphate pathway (PPP) all change in parallel during the lactation cycle. Similarly, after 3 and 5 days duration of streptozotocin-induced diabetes, ending on day 10 of lactation, there were parallel declines in PPRibP content, PPRibP synthetase and PPP activity. The effect of streptozotocin was prevented by pretreatment with nicotinamide and partially reversed by insulin administration. Addition of insulin to lactating rat mammary-gland slices incubated in vitro significantly raised the PPRibP content (+47%) and the activity of the PPP (+40%); phenazine methosulphate, which gives a 2-fold increase in PPP activity, raised the PPRibP content of lactating mammary gland slices by approx. 3-fold. It is concluded that Rib5P, generated in the oxidative segment of the PPP, is an important determinant of PPRibP synthesis in the lactating rat mammary gland and that insulin plays a central role in the regulation of the bioavailability of this precursor of nucleotide and nucleic acid synthesis.     

Multisite control of the Crabtree effect in ascites hepatoma cells.

AS-30D hepatoma cells, a highly oxidative and fast-growing tumor line, showed glucose-induced and fructose-induced inhibition of oxidative phosphorylation (the Crabtree effect) of 54% and 34%, respectively. To advance the understanding of the underlying mechanism of this process, the effect of 5 mM glucose or 10 mM fructose on the intracellular concentration of several metabolites was determined. The addition of glucose or fructose lowered intracellular Pi (40%), and ATP (53%) concentrations, and decreased cytosolic pH (from 7.2 to 6.8). Glucose and fructose increased the content of AMP (30%), glucose 6-phosphate, fructose 6-phosphate and fructose 1,6-bisphosphate (15, 13 and 50 times, respectively). The cytosolic concentrations of Ca2+ and Mg2+ were not modified. The addition of galactose or glycerol did not modify the concentrations of the metabolites. Mitochondria isolated from AS-30D cells, incubated in media with low Pi (0.6 mM) at pH 6.8, exhibited a 40% inhibition of oxidative phosphorylation. The data suggest that the Crabtree effect is the result of several small metabolic changes promoted by addition of exogenous glucose or fructose.     

Resistance to quaternary ammonium compounds in Staphylococcus spp. isolated from the food industry and nucleotide sequence of the resistance plasmid pST827

K.A. ALBASHERI AND W.J. MITCHELL. 1995. Maltose metabolism in the obligate anaerobe Clostridium acetobutylicum was studied. The sugar is accumulated via an energy-dependent transport process which is not a phosphotransferase. Cell extracts were incapable of phosphorylating maltose in the presence or absence of phosphoenolpyruvate or ATP, but exhibited hydrolytic activity against a range of glucoside substrates. The activity was predominantly in the soluble fraction of cell extracts, indicating a cytoplasmic location in the cell. Gel filtration on Sephadex G100 indicated the presence of at least two α-glucosidases. One enzyme (maltase) was active with maltose and maltotriose, while the other (pNPGase) hydrolysed isomaltose and several glucoside analogues, but neither showed activity against starch. Both glucosidases were induced by isomaltose, maltose, glucose and starch, but not by xylose, sucrose or cellobiose. In the presence of both glucose and maltose, growing cells showed a preference for glucose, apparently due to regulation of maltose transport, which did not occur in glucose-grown cells.     

马克斯克鲁维酵母GX-UN120糖转运蛋白基因的克隆及表征

【背景】马克斯克鲁维酵母(Kluyveromyces marxianus)具有完整的木糖代谢途径,可以高效利用木质纤维素中的木糖,因此对其糖转运蛋白基因的研究或可有效解决酵母木糖转运的相关问题。【目的】根据马克斯克鲁维酵母DMKU3-1042中KLMA＿70145和KLMA＿80101基因位点的功能预测,获得马克斯克鲁维酵母GX-UN120相应的糖转运蛋白基因序列并探究其功能。【方法】将转运蛋白基因分别克隆表达至酿酒酵母EBY.VW4000中考察重组菌株生长特性,以此间接评价对应转运蛋白的转运能力。【结果】Km＿SUT2基因编码的糖转运蛋白可有效提高宿主细胞转运木糖、阿拉伯糖、山梨糖、核糖、乳糖和葡萄糖的能力,但却不能转运甘露糖、果糖、蔗糖和半乳糖。类似地,Km＿SUT3基因编码的糖转运蛋白可提高细胞转运木糖、阿拉伯糖、山梨糖、半乳糖、核糖、乳糖和葡萄糖的能力,但却不能转运甘露糖和果糖。然而在葡萄糖存在的条件下,重组菌株对各种碳源的利用均受抑制,但Km＿SUT3转运木糖和核糖过程中受葡萄糖的抑制作用较小。【结论】马克斯克鲁维酵母GX-UN120中转运蛋白Km＿SUT2和Km＿SUT3可...     

Effects of various metabolic conditions and of the trivalent arsenical melarsen oxide on the intracellular levels of fructose 2,6-bisphosphate and of glycolytic intermediates in Trypanosoma brucei

Upon differential centrifugation of cell-free extracts of Trypanosoma brucei, 6-phosphofructo-2-kinase and fructose-2,6-bisphosphatase behaved as cytosolic enzymes. The two activities could be separated from each other by chromatography on both blue Sepharose and anion exchangers. 6-phosphofructo-2-kinase had a Km for both its substrates in the millimolar range. Its activity was dependent on the presence of inorganic phosphate and was inhibited by phosphoenolpyruvate but not by citrate or glycerol 3-phosphate. The Km of fructose-2,6-bisphosphatase was 7 microM; this enzyme was inhibited by fructose 1,6-bisphosphate (Ki = 10 microM) and, less potently, by fructose 6-phosphate, phosphoenolpyruvate and glycerol 3-phosphate. Melarsen oxide inhibited 6-phosphofructo-2-kinase (Ki less than 1 microM) and fructose-2,6-bisphosphatase (Ki = 2 microM) much more potently than pyruvate kinase (Ki greater than 100 microM). The intracellular concentrations of fructose 2,6-bisphosphate and hexose 6-phosphate were highest with glucose, intermediate with fructose and lowest with glycerol and dihydroxyacetone as glycolytic substrates. When added with glucose, salicylhydroxamic acid caused a decrease in the concentration of fructose 2,6-bisphosphate, ATP, hexose 6-phosphate and fructose 1,6-bisphosphate. These studies indicate that the concentration of fructose 2,6-bisphosphate is mainly controlled by the concentration of the substrates of 6-phosphofructo-2-kinase. The changes in the concentration of phosphoenolpyruvate were in agreement with the stimulatory effect of fructose 2,6-bisphosphate on pyruvate kinase. At micromolar concentrations, melarsen oxide blocked almost completely the formation of fructose 2,6-bisphosphate induced by glucose, without changing the intracellular concentrations of ATP and of hexose 6-phosphates. At higher concentrations (3-10 microM), this drug caused cell lysis, a proportional decrease in the glycolytic flux, as well as an increase in the phosphoenolypyruvate concentrations which was restricted to the extracellular compartment. Similar changes were induced by digitonin. It is concluded that the lytic effect of melarsen oxide on the bloodstream form of T. brucei is not the result of an inhibition of pyruvate kinase.     

Factors affecting hexose phosphorylation in Acetobacter xylinum

Fructose was oxidized and converted to cellulose by cells of Acetobacter xylinum grown on fructose or succinate, but not by cells grown on glucose. In resting fructose-grown cells, glucose strongly suppressed fructose utilization. Extracts obtained from fructose- or succinate-grown cells catalyzed the adenosine triphosphate (ATP)-dependent formation of the 6-phosphate esters of glucose and fructose, whereas glucose-grown cell extracts phosphorylated glucose but not fructose. Fructokinase and glucokinase activities were separated and partially purified from cells grown on glucose, fructose, or succinate. Whereas fructokinase phosphorylated fructose only, glucokinase was active towards glucose and less active towards mannose and glucosamine. The optimal pH for the fructokinase was 7.4 and for the glucokinase was 8.5. The K(m) values for the fructokinase were: fructose, 6.2 mm; and ATP, 0.83 mm. The K(m) values for the glucokinase were: glucose, 0.22 mm; and ATP, 4.2 mm. Fructokinase was inhibited by glucose, glucosamine, mannose, and deoxyglucose in a manner competitive with respect to fructose, with K(i) values of 0.1, 0.14, 0.5, and 7.5 mm, respectively. Adenosine diphosphate (ADP) and adenosine monophosphate (AMP) inhibited both kinases noncompetitively with respect to ATP. The K(i) values were: 1.8 mm (ADP) and 2.1 mm (AMP) for fructokinase, and 2.2 mm (ADP) and 9.6 mm (AMP) for glucokinase. Fructose metabolism in A. xylinum appears to be regulated by the synthesis and activity of fructokinase.