D-ribulose-5-phosphate 3-epimerase Research Articles

Subcellular distribution of enzymes of the oxidative pentose phosphate pathway in root and leaf tissues

sketolase, ribose 5-phosphate isomerase, ribulose 5-phosphate 3-epimerase) appear to be restricted to between phosphorylated 3-, 4-, 5-, 6-, and 7-carbon sugars catalysed by the enzymes ribose 5-phosphate isomerase the plastid. In tobacco root and leaf, however, the non-oxidative enzymes were found in the cytosolic as (Rib5P isomerase), ribulose 5-phosphate 3-epimerase (Rul5P 3-epimerase), transaldolase ( TA), and transketolwell as the plastidic compartments. In the absence of ribose 5-phosphate isomerase and ribulose ase ( TK ). With the exception of the transaldolase, these reversible enzymes are amphibolic, and also play a part 5-phosphate 3-epimerase in the cytosol, the product of the oxidative limb of the pathway (ribulose in the Calvin cycle. Their function as part of the pentose phosphate pathway is to provide carbon skeletons for the 5-phosphate) must be transported into a compartment capable of utilizing it. Ribulose 5-phosphate was sup- shikimate pathway via erythrose 4-phosphate, and nucleotide synthesis utilizing ribose 5-phosphate, as well as plied to isolated intact pea root plastids and was shown to be capable of supporting nitrite reduction. recycling of sugar phosphate intermediates for use in the glycolytic pathway (ap Rees, 1985). The kinetics of ribulose 5-phosphate-driven nitrite reduction in isolated pea root plastids suggested that The enzymes of the oxidative portion of the pathway are commonly found in both the cytosolic and plastidic the metabolite was translocated across the plastid envelope in a carrier-mediated transport process, fractions of photosynthetic (Herbert et al., 1979) and non-photosynthetic cells (Ashihara and Komamine, 1976; indicating the presence of a translocator capable of transporting pentose phosphates.

Identification of a Catalytic Aspartyl Residue ofd-Ribulose 5-Phosphate 3-Epimerase by Site-directed Mutagenesis

Guided by comparative sequence considerations, we have examined the possibility of a catalytic role of Asp186 of D-ribulose 5-phosphate epimerase by site-directed mutagenesis of the recombinant spinach enzyme. Accordingly, D186A, D186N, and D186E mutants of the epimerase were constructed, purified, and characterized; as judged by their electrophoretic mobilities the mutants are properly assembled into octamers like the wild-type enzyme. Based on the extent of internal quenching of Trp fluorescence, the conformational integrity of the wild-type enzyme is preserved in the mutants. The wild-type kcat of 7.1 x 10(3) s-1 is lowered to 3.3 x 10(-4) s-1 in D186A, 0.13 s-1 in D186N, and 1.1 s-1 in D186E; as gauged by D186A, altogether lacking a functional side chain at position 186, the beta-carboxyl of Asp186 facilitates catalysis by >10(7)-fold. Relative to the wild-type enzyme, the Km for D-ribulose 5-phosphate is essentially unaltered with D186N and D186E but increased 10-fold with D186A. Apart from their impairments in epimerase activity, the mutants are unable to catalyze exchange between solvent protons and the C3 proton of substrates. This deficiency and the differential alterations of kinetic parameters among the mutants are consistent with Asp186 serving as an electrophile to facilitate alpha-proton abstraction. This study is the first to identify a catalytic group of the epimerase.

Purification, properties and in situ localization of the amphibolic enzymes D-ribulose 5-phosphate 3-epimerase and transketolase from spinach chloroplasts.

The amphibolic enzymes D-ribulose 5-phosphate 3-epimerase and transketolase have been purified from stroma extracts of spinach chloroplasts using ammonium sulfate fractionation and FPLC. For the native enzymes, a molecular mass of 180 kDa for epimerase and 160 kDa for transketolase was found and the molecular masses of the subunits was determined to be 23 kDa for epimerase and 74 kDa for transketolase. Protein sequencing of the purified chloroplast enzymes revealed the NH2-terminal amino acid sequences of mature epimerase (NH2-TSRVDKFSKSDIIVSP) and transketolase (NH2-AAVEALESTDTDQLVEG). The enzymic properties of both enzymes such as Km values or pH optima, were found to be very similar to those for epimerases and transketolases from other sources, including yeast and animal cells. In contrast to the light-activated enzymes of the Calvin cycle, the activity of these amphibolic enzymes was not redox-dependent. Immunogold electron microscopy on spinach leaf thin sections revealed that about 90% of the total epimerase and transketolase, and 96% of the total chloroplast H+-ATP synthase portion CF1 are associated with thylakoid membranes in situ. Ribulose-1,5-bisphosphate carboxylase/oxygenase, in contrast, was evenly distributed throughout chloroplasts. These and other results indicate that minor chloroplast enzymes are arranged in a thin layer on thylakoid membrane surfaces in vivo.

Significance of the Non-Oxidative Pentose Phosphate Pathway in Aspergillus oryzae Grown on Different Carbon Sources

Specific enzyme activities of the non-oxidative pentose phosphate pathway in Aspergillus oryzae mycelia grown on different carbon sources were determined. Mycelia grown on glucose, mannitol and ribose show the highest specific activities, ribose 5-phosphate isomerase being specially very enhanced. Moreover, transketolase, transaldolase, ribose 5-phosphate isomerase and ribulose 5-phosphate 3-epimerase were determined in different developmental stages of mycelia grown on glucose, mannitol and ribose. The non-oxidative pentose phosphate pathway is more active during conidiogenesis, except for ribulose 5-phosphate 3-epimerase, suggesting a fundamental role of this pathway during that stage to supply pentoses for nucleic acids biosynthesis. A general decrease of the enzyme activities was found in sporulated mycelia. Arabinose 5-phosphate was tested as metabolite of the pentose pathway. This pentose phosphate was not converted into hexose phosphates or triose phosphates and inhibits significantly the ribose 5-phosphate utilization, being therefore unappropriate to support the Aspergillus oryzae growth.

The measurement of xylulose 5-phosphate, ribulose 5-phosphate, and combined sedoheptulose 7-phosphate and ribose 5-phosphate in liver tissue

A modification of the method of Kauffman et al. (F. C. Kauffman, J. G. Brown, J. V. Passonneau, and O. H. Lowry (1969) J. Biol. Chem. 244, 3647–3653) for the spectrophotometric determination of xylulose 5-phosphate, ribulose 5-phosphate, and combined ribose 5-phosphate and sedoheptulose 7-phosphate in tissue extract is presented. Using commercially available enzymes all three assays come to a clear endpoint with the assays described. Values for these metabolites in liver in three dietary states are reported; 48 h starved, ad libitum feeding of standard NIH rat ration, and meal feeding of a fat-free diet. Xylulose 5-phosphate values were 3.8 ± 0.3, 8.6 ± 0.3, and 66.3 ± 8.3 nmol/g. Ribulose 5-phosphate values were 3.4 ± 0.3, 5.8 ± 0.2, and 37.1 ± 5.3 nmol/g. Combined ribose 5-phosphate and sedoheptulose 7-phosphate were 29.3 ± 0.3, 38.2 ± 1.2, and 108.2 ± 14.5 nmol/g. The ratio of measured tissue content of [xylulose 5-phosphate]/[ribulose 5-phosphate] was found to be 1.12 ± 0.07 in starved animals, 1.48 ± 0.04 in ad libitum fed animals and 1.78 ± 0.03 in low-fat meal fed animals. These data are in good agreement with the range of equilibrium constants reported for this reaction, suggesting that the ribulose 5-phosphate 3-epimerase reaction (EC 5.1.3.1) is a near equilibrium reaction despite a more than 10-fold change in the tissue content of these metabolites.

Improved determination of transketolase activity in erythrocytes.

We describe a new and better method for determining transketolase (EC 2.2.1.1) activity in human erythrocytes. Heating the hemolysate (55 degrees C, 5 min) inactivates transaldolase (EC 2.2.1.2), the enzyme that catalyzes the formation of fructose 6-phosphate and erythrose 4-phosphate from sedoheptulose 7-phosphate and glyceraldehyde 3-phosphate. The net effect is that the quantity of sedoheptulose 7-phosphate formed more precisely represents the transketolase activity, which is unaffected under these conditions. Use of ribosephosphate isomerase (EC 5.3.1.6) and ribulose-phosphate 3-epimerase (EC 5.1.3.1) to establish an equilibrium among the pentoses allowed us to confirm the stoichiometry of the transketolase reaction. We also discuss the effect of thiamin pyrophosphate, which is used to reflect thiamin deficiency.

Purification, properties and assay of D-ribulose 5-phosphate 3-epimerase from human erythrocytes.

A direct assay procedure is described for D-ribulose 5-phosphate 3-epimerase (EC 5.1.3.1) which exploits differences in the c.d. spectra of substrate and product. The enzyme has been purified from human erythrocytes and was resolved by gel filtration and sucrose-density-gradient centrifugation into a major component of apparent Mr 45 000 and a minor component of Mr 23 000. Electrophoresis in sodium dodecyl sulphate gave a single component corresponding to Mr 23 000. Kinetic and sucrose-density-gradient centrifugation data indicate dissociation of the dimeric form of the enzyme into monomers of low specific activity; substrate favours the active dimeric form of the enzyme. At concentrations of the enzyme where both forms of the enzyme are present initial velocity data yielded a Hill plot with an interaction coefficient of approx. 2.0, indicating co-operative binding of substrate under these conditions.

The effect of trans-stilbene oxide and other structurally related inducers of drug-metabolizing enzymes on the pentose phosphate pathway and other enzymes of carbohydrate metabolism

trans-Stilbene oxide has been found earlier to be a new type of inducer of drug-metabolizing systems. Here we demonstrate that treatment of rats with this xenobiotic results in an increase in the activity of the cytosolic glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, the first and third enzymes in the pentose phosphate pathway, to 350% and 170% of the control values, respectively. At the same time microsomal glucose 6-phosphate dehydrogenase activity was unaffected by administration of trans-stilbene oxide or benzil. The time course and dose-response of the increases in glucose 6-phosphate and 6-phosphogluconate dehydrogenase activities have been characterized. The activities of ribulose 5-phosphate 3-epimerase and ribose 5-phosphate ketol isomerase, enzymes further along in the pentose phosphate pathway, were not significantly affected by trans-stilbene oxide or benzil. An investigation of the effect of treating rats with different metabolites of stilbene and with other structurally related compounds on hepatic cytosolic glucose 6-phosphate dehydrogenase activity revealed the structural features which are important for increasing this activity. Finally, it was found that administration of trans-stilbene oxide did not affect the activities of glucokinase and phosphoglucose isomerase, the two glycolytic enzymes which can produce glucose 6-phosphate, the link between glycolysis and the pentose phosphate shunt.

A ribulose 5-phosphate 3-epimerase (RPE) locus is on human chromosome 2.

A ribulose 5-phosphate 3-epimerase (RPE) locus is on human chromosome 2.

Biochemical genetics of the pentose phosphate cycle: human ribose 5-phosphate isomerase (RPI) and ribulose 5-phosphate 3-epimerase (RPE).

1. Staining procedures are described for the detection after starch-gel electrophoresis of ribose-5-phosphate isomerase (RPI) and ribulose 5-phosphate 3-epimerase (RPE). 2. Both RPI and RPE were detected in all human tissues including red cells, lymphocytes and fibroblasts. 3. No evidence was found for more than one structural gene locus for either enzyme. 4. No allelic variants of either enzyme were found in erythrocyte lysates from over 200 unrelated individuals. 5. Preliminary data are presented which suggest that differences in tissue RPE isozyme patterns may be due to endogenous proteolytic activity. 6. Electrophoretic analysis of RPE and RPI isozyme patterns in extracts of man/mouse hybrid cells indicates that RPE is probably a dimer and RPI may also be polymeric.

The affinity chromatography of transketolase

A number of possible affinity adsorbents for transketolase (sedoheptulose-7-phospate: d-glyceraldehyde-3-phosphateglycolaldehydetransferase, EC 2.2.1.1) were prepared. The behaviour of the enzyme from Candida utilis and from Baker's yeast on columns of these and of Blue Sepharose CL-6B was examined, together with the behaviour of the contaminating enzyme, ribulose 5-phosphate 3-epimerase (EC 5.1.3.1). A procedure for removing bound thiamine pyrophosphate by dialysis against EDTA was developed. The competitive inhibition of transketolase by oxythiamine and neopyrithiamine was measured and the K i values obtained of 1.4 and 4.3 mM, respectively, were compared with the affinity of adsorbents prepared from these two inhibitors. Adsorbents containing bound thiamine pyrophosphate were relatively ineffective but those containing thiamine pyrophosphate were relatively ineffective but those containing epoxy-linked neopyrithiamine and d-ribose 5-phosphate adsorbed the enzyme at pH 7.4 and it could be eluted in a specific manner.

The pentose phosphate pathway in regenerating skeletal muscle.

1. The activities of the oxidative enzymes (glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase) and of the non-oxidative enzymes (transaldolase, tranketolase, ribose 5 phosphate isomerase and ribulose 5-phosphate 3-epimerase) of the pentose phosphate pathway were measured at various times during the first 24h of skeletal-muscle regeneration after administration of Marcaine, a mytoxic local anesthetic. 2. The activities of the oxidative enzymes increased after Marcaine injection and rose to 9 times control activities by 24h. 3. The activities of all non-oxidative enzymes were increased after Marcaine administration, but to a much smaller extent than the oxidative enzymes (1.1-1.7-fold). 4. Histochemical analysis localized glucose 6-phosphate dehydrogenase activity within muscle fibres of control and Marcaine-treated muscles. 5. Cycloheximide or actinomycin D prevented the increase in oxidative enzyme activities, suggesting a requirement for synthesis of protein and RNA.

A spectrophotometric procedure for following the d-ribulose 5-phosphate 3-epimerase reaction in the direction of ribulose 5-phosphate formation

A continuous spectrophotometric procedure for following the conversion of d-xylulose 5-phosphate to d-ribulose 5-phosphate by d-ribulose 5-phosphate 3-epimerase is described. Transketolase, ribose 5-phosphate ketol isomerase, glycerol 3-phosphate dehydrogenase, and triose phosphate isomerase were used as coupling enzymes and both practical and theoretical criteria for the validity of a coupled assay were satisfied. The initial velocity of the reaction was determined at a number of d-xylulose 5-phosphate concentrations and K m and V values of 0.15 ± 0.02 (SEM) m m d-xylulose 5-phosphate and 10.5 ± 0.6 (SEM) μmoles/min/mg protein were calculated from a reciprocal plot.

On the Mechanism of the Pentose Phosphate Epimerases

Abstract The mechanism of the l-ribulose 5-phosphate 4-epimerase has been examined. In agreement with previous observations (Mcdonough, M. W., and Wood, M. A. (1961) J. Biol. Chem. 236, 1220) no exchange of hydrogen with H2O is observed. Suitable double label experiments indicate that hydrogen transfer in the reaction is intramolecular. The data for kinetics of the exchange of the hydrogen at C-3 of substrate catalyzed by a d-ribulose 5-phosphate 3-epimerase have been examined. The data indicate that the enzyme must contain two hydrogen donors (acceptors) which interact with the hydrogen at carbon 3 of d-ribulose 5-phosphate and d-xylulose 5-phosphate, respectively.

The Pentose Cycle in Adult Ascaris suum

The presence of all the enzymes necessary for a functional pentose cycle in the muscular, reproductive, and digestive systems of adult male and female Ascaris suum was established. The presence of the hexose monophosphate shunt (pentose cycle) in adult female ascarids has been suggested. de Ley and Vercruysse (1955) found glucose-6-phosphate dehydrogenase (G-6-PD) and 6-phosphogluconate dehydrogenase (6-PGD) activities in the muscular and reproductive systems of adult female Ascaris lumbricoides obtained from pig intestine. Entner (1957), using muscle from A. lumbricoides, confirmed the presence of G-6PD and 6-PGD and, in addition, showed ribosephosphate isomerase (I), ribulose phosphate3-epimerase (E), and transketolase (TK) activities. However, as transaldolase (TA) activity was not measured, the presence of an intact pentose cycle was not conclusively established. This report presents comparative data on the enzymes noted above, as well as on transaldolase (TA) activity in the muscular, reproductive, and digestive systems of adult male and female Ascaris suum. MATERIALS AND METHODS

The pentose phosphate pathway of glucose metabolism. Hormonal and dietary control of the oxidative nd non-oxidative reactions and related enzymes of the cycle in adipose tissue.

1. Measurements were made of the activities of the enzymes of the pentose phosphate pathway concerned in both the oxidative (glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase) and the non-oxidative (ribose 5-phosphate isomerase, ribulose 5-phosphate epimerase, transketolase and transaldolase) reactions of this pathway, together with hexokinase and phosphoglucose isomerase, in adipose tissue in a variety of nutritional and hormonal conditions. 2. Starvation for 2 days caused a significant decrease in the activities of all the enzymes of the pentose phosphate pathway, with the exception of glucose 6-phosphate dehydrogenase, when expressed as activity/2 fat-pads; only the activities of ribose 5-phosphate isomerase and ribulose 5-phosphate epimerase were significantly decreased on the basis of activity/mg. of protein. Re-feeding with a high-carbohydrate or high-fat diet for 3 days restored the activity of all the enzymes of the pentose phosphate pathway to the range of the control values, with the exception of transketolase, which showed a marked ;overshoot' in rats re-fed with carbohydrate. Starvation for 3 days caused a marked decrease in the activities of glucose 6-phosphate dehydrogenase and transketolase. 3. On the basis of activity/two fat-pads, alloxan-diabetes caused a marked decrease, to about half the control value, in the activities of all the enzymes concerned in the pentose phosphate pathway, transketolase showing the smallest decrease; hexokinase and phosphoglucose isomerase activities were also decreased. Treatment with insulin for 3 and 7 days raised the activities to normal or supranormal values, transketolase showing the most marked ;overshoot' effect. On the basis of activity/mg. of protein the activity of none of the enzymes was significantly decreased in alloxan-diabetes; transketolase and transaldolase activities were raised above the control values. With insulin treatment for 3 or 7 days the activities of all the enzymes were significantly increased, except that of ribulose 5-phosphate epimerase at the shorter time-interval. Glucagon treatment did not alter any of the enzyme activities expressed on either basis. 4. Thyroidectomy caused a decrease of 30-40% in the activities of enzymes of the pentose phosphate pathway, except for transketolase activity, which fell to 50% of the control value. Little change occurred in adipose-tissue weight or protein content. 5. Adrenalectomy caused a decrease of 40% in the activity of glucose 6-phosphate dehydrogenase and of 20-30% in the activities of the remaining enzymes of the pentose phosphate pathway; hexokinase activity was also decreased. Treatment with cortisone for 3 days did not significantly raise the activity from that found in adrenalectomized rats. Treatment of normal rats with high doses of cortisone had no significant effect on the activities of the enzymes of the pentose phosphate pathway in adipose tissue. 6. The changes in enzyme activities are discussed in relation to: (a) the concept of constant-proportion groups of enzymes; (b) the known changes in the flux of glucose through alternative metabolic pathways; (c) the pattern of change found in liver with similar hormonal and dietary conditions.

The pentose phosphate pathway of glucose metabolism. Influence of a growth-hormone-secreting pituitary tumour on the oxidative and non-oxidative reactions of the cycle in liver.

1. Measurements were made of the activities of enzymes of the pentose phosphate cycle, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, ribose 5-phosphate isomerase, ribulose 5-phosphate epimerase, transketolase and transaldolase, as well as of the related or competing enzymes glucokinase, hexokinase, phosphoglucose isomerase and phosphoglucomutase, in control rats and in rats bearing the growth-hormone- and prolactin-secreting pituitary tumour MtTW5, to study the effect of high endogenous concentrations of growth hormone on this pathway in liver. 2. There was a twofold increase in liver weight. Glucokinase activity/g. of liver decreased to half the control value in the experimental group, although on a total liver basis it remained unchanged. Hexokinase activity increased in parallel with the liver weight, so that the total activity was doubled in rats with a high endogenous concentration of growth hormone. No differences in response were found between heat-stable and heat-labile forms of hexokinase. 3. The activity/g. of liver of the two oxidative enzymes of the pathway decreased slightly in the experimental group, but this was offset by the increase in liver weight, and the resultant effect was a 50% increase in the total activity. 4. Of the non-oxidative enzymes of the cycle the most marked increase on a total liver basis was in ribose 5-phosphate isomerase activity, to 2.5 times the control value. Ribulose 5-phosphate epimerase activity showed the smallest increase. Transketolase and transaldolase activities were also increased. The latter is the rate-limiting enzyme of the non-oxidative reactions of the cycle in these animals. 5. The results are discussed in relation to the glycolytic pathway and synthesis of glycogen, and more particularly to the increased requirement for ribose 5-phosphate for RNA synthesis.

The purification of transketolase from Candida utilis.

Transketolase (EC 2.2.1.1) was purified 12-fold from an extract of dried Candida utilis by two fractionations with acetone followed by chromatography on DEAE-Sephadex. The fractions from the column were free from D-ribose 5-phosphate ketol isomerase and D-ribulose 5-phosphate 3-epimerase and could be used for the assay of D-xylulose 5-phosphate and of the epimerase. Three peaks of transketolase activity were eluted from the chromatography column; the material from each peak had a Michaelis constant for D-xylulose 5-phosphate close to the mean value for the three peaks of 6.8 × 10−5 M and gave the same two-banded pattern on cellulose acetate electrophoresis. When transaldolase was present in the material placed on the column, it appeared with transketolase in each of the three peaks. The enzyme could be stored for several months, in solution frozen at −20°. Dialysis against water caused a loss of activity which could be restored by the addition of thiamine pyrophosphate. The enzyme catalyzed the condensation of hydroxypyruvate with D-glyceraldehyde phosphate to form D-xylulose 5-phosphate.

The pentose phosphate pathway of glucose metabolism. Hormonal and dietary control of the oxidative and non-oxidative reactions of the cycle in liver.

1. Measurements were made of the non-oxidative reactions of the pentose phosphate cycle in liver (transketolase, transaldolase, ribulose 5-phosphate epimerase and ribose 5-phosphate isomerase activities) in a variety of hormonal and nutritional conditions. In addition, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities were measured for comparison with the oxidative reactions of the cycle; hexokinase, glucokinase and phosphoglucose isomerase activities were also included. Starvation for 2 days caused significant lowering of activity of all the enzymes of the pentose phosphate cycle based on activity in the whole liver. Re-feeding with a high-carbohydrate diet restored all the enzyme activities to the range of the control values with the exception of that of glucose 6-phosphate dehydrogenase, which showed the well-known ;overshoot' effect. Re-feeding with a high-fat diet also restored the activities of all the enzymes of the pentose phosphate cycle and of hexokinase; glucokinase activity alone remained unchanged. Expressed as units/g. of liver or units/mg. of protein hexokinase, glucose 6-phosphate dehydrogenase, transketolase and pentose phosphate isomerase activities were unchanged by starvation; both 6-phosphogluconate dehydrogenase and ribulose 5-phosphate epimerase activities decreased faster than the liver weight or protein content. 2. Alloxan-diabetes resulted in a decrease of approx. 30-40% in the activities of 6-phosphogluconate dehydrogenase, ribose 5-phosphate isomerase, ribulose 5-phosphate epimerase and transketolase; in contrast with this glucose 6-phosphate dehydrogenase, transaldolase and phosphoglucose isomerase activities were unchanged. Treatment of alloxan-diabetic rats with protamine-zinc-insulin for 3 days caused a very marked increase to above normal levels of activity in all the enzymes of the pentose phosphate pathway except ribulose 5-phosphate epimerase, which was restored to the control value. Hexokinase activity was also raised by this treatment. After 7 days treatment of alloxan-diabetic rats with protamine-zinc-insulin the enzyme activities returned towards the control values. 3. In adrenalectomized rats the two most important changes were the rise in hexokinase activity and the fall in transketolase activity; in addition, ribulose 5-phosphate epimerase activity was also decreased. These effects were reversed by cortisone treatment. In addition, in cortisone-treated adrenalectomized rats glucokinase activity was significantly lower than the control value. 4. In thyroidectomized rats both ribose 5-phosphate isomerase and transketolase activities were decreased; in contrast with this transaldolase activity did not change significantly. Hypophysectomy caused a 50% fall in transketolase activity that was partially reversed by treatment with thyroxine and almost fully reversed by treatment with growth hormone for 8 days. 5. The results are discussed in relation to the hormonal control of the non-oxidative reactions of the pentose phosphate cycle, the marked changes in transketolase activity being particularly outstanding.

Crystalline L-Ribulose 5-Phosphate 4-Epimerase from Escherichia coli

Abstract l-Ribulose 5-phosphate 4-epimerase has been crystallized from l-arabinose-induced cells of Escherichia coli B/r strain F' araB-24/araB-24 after a 40-fold purification. The enzyme is homogeneous in the ultracentrifuge and 98% pure by acrylamide gel disc electrophoresis. The molecular weight determined by sedimentation equilibrium is 1.03 ± 0.01 x 105. The enzyme is free of d-ribulose 5-phosphate 3-epimerase activity, does not exhibit any cofactor requirement, and shows maximal activity from pH 7 to 10. An amino acid analysis is presented.