Variants of transketolase from human erythrocytes

Pharmacological Doses of Thiamine Benefit Patients with the Charcot-Marie-Tooth Neuropathy by Changing Thiamine Diphosphate Levels and Affecting Regulation of Thiamine-Dependent Enzymes

Charcot-Marie-Tooth (CMT) neuropathy is a polygenic disorder of peripheral nerves with no effective cure. Thiamine (vitamin B1) is a neurotropic compound that improves neuropathies. Our pilot study characterizes therapeutic potential of daily oral administration of thiamine (100 mg) in CMT neuropathy and its molecular mechanisms. The patient hand grip strength was determined before and after thiamine administration along with the blood levels of the thiamine coenzyme form (thiamine diphosphate, ThDP), activities of endogenous holo-transketolase (without ThDP in the assay medium) and total transketolase (with ThDP in the assay medium), and transketolase activation by ThDP [1 - (holo-transketolase/total transketolase),%], corresponding to the fraction of ThDP-free apo-transketolase. Single cases of administration of sulbutiamine (200 mg) or benfotiamine (150 mg) reveal their effects on the assayed parameters within those of thiamine. Administration of thiamine or its pharmacological forms increased the hand grip strength in the CMT patients. Comparison of the thiamin status in patients with different forms of CMT disease to that of control subjects without diagnosed pathologies revealed no significant differences in the average levels of ThDP, holo-transketolase, or relative content of holo and apo forms of transketolase. However, the regulation of transketolase by thiamine/ThDP differed in the control and CMT groups: in the assay, ThDP activated transketolase from the control individuals, but not from CMT patients. Thiamine administration paradoxically decreased endogenous holo-transketolase in CMT patients; this effect was not observed in the control group. Correlation analysis revealed sex-specific differences in the relationship between the parameters of thiamine status in both the control subjects and patients with the CMT disease. Thus, our findings link physiological benefits of thiamine administration in CMT patients to changes in their thiamine status, in particular, the blood levels of ThDP and transketolase regulation.

Erythrocyte transketolase activity coefficient (ETKAC) assay protocol for the assessment of thiamine status

Vitamin B1 (thiamine) is an essential nutrient that acts as a cofactor for a number of metabolic processes, particularly in energy metabolism. Symptoms of classic thiamine deficiency are recognized as beriberi, although clinical symptoms are nonspecific and recognition of subclinical deficiency is difficult. Therefore, reliable biomarkers of thiamine status are required. Thiamine diphosphate is a cofactor for transketolase, including erythrocyte transketolase (ETK). The ETK activity assay as an indirect, functional marker of thiamine status has been used for over 50 years. The ETK activity assay provides a sensitive and specific biomarker of thiamine status; however, there is a lack of consensus over the cutoffs for deficiency, partly due to a lack of assay harmonization. Here, we provide a step-by-step protocol for the measurement of ETK activity and the calculation of the ETK activity coefficient, including detailed explanations of equipment and chemicals required and guidance for quality control procedures. Harmonization of the protocol will provide the basis for the development of internationally recognized cutoffs for thiamine insufficiency. The establishment of quality control materials and a quality assurance scheme are recommended to provide reliability. This will ensure that the ETK activity assay remains an important method for the assessment of thiamine status.

Comparison of Thiamin Diphosphate High-Performance Liquid Chromatography and Erythrocyte Transketolase Assays for Evaluating Thiamin Status in Malaria Patients without Beriberi

Thiamin deficiency, or beriberi, is an increasingly re-recognized cause of morbidity and mortality in the developing world. Thiamin status has traditionally been measured through the erythrocyte activation assay (ETKA) or basal transketolase activity (ETK), which indirectly measure thiamin diphosphate (TDP). Thiamin diphosphate can also be measured directly by high-performance liquid chromatography (HPLC), which may allow a more precise estimation of thiamin status. We compared the direct measurement of TDP by HPLC with basal ETK activity and ETKA in 230 patients with Plasmodium falciparum malaria in rural southern Laos without overt clinical beriberi, as part of a trial of thiamin supplementation. Admission thiamin status measured by basal ETK activity and ETKA (α) were compared with thiamin status assessed by the measurement of TDP by HPLC. 55% of 230 included patients were male, and the median age was 10 (range 0.5–73) years. Using α ≥ 25% as the gold standard of thiamin deficiency, the sensitivity of TDP < 275 ng/gHb as a measure of thiamin deficiency was 68.5% (95% CI: 54.4–80.5%), with specificity of 60.8 (95% CI: 53.2–68.1%). There was a significant inverse correlation between the results of the two tests (Kendall’s tau = −0.212, P < 0.001). Basal ETK activity was also significantly positively correlated with TDP levels (Kendall’s tau = 0.576, P < 0.001). Thiamin diphosphate measurement may have a role in measuring thiamin levels in clinical settings. Further studies evaluating TDP concentration in erythrocytes with basal ETK activity and ETKA (α) in beriberi patients would help establish comparative values of these assays.

The Role of Thiamine and Effects of Deficiency in Dogs and Cats

Recent pet food recalls for insufficient dietary thiamine have highlighted the importance of adequate thiamine intake in dogs and cats, as thiamine is an essential dietary nutrient with a critical role in energy metabolism. Prolonged thiamine deficiency leads to clinical signs that can span several organ systems, and deficiency can be fatal if not reversed. In this review, the current knowledge of thiamine metabolism will be summarized. Dietary recommendations for dogs and cats will be discussed, and the risk factors and clinical signs associated with thiamine deficiency will be examined.

Thiamin in Clinical Practice

Thiamin is a water-soluble vitamin also known as vitamin B1. Its biologically active form, thiamin pyrophosphate (TPP), is a cofactor in macronutrient metabolism. In addition to its coenzyme roles, TPP plays a role in nerve structure and function as well as brain metabolism. Signs and symptoms of thiamin deficiency (TD) include lactic acidosis, peripheral neuropathy, ataxia, and ocular changes (eg, nystagmus). More advanced symptoms include confabulation and memory loss and/or psychosis, resulting in Wernicke's encephalopathy and/or Wernicke's Korsakoff syndrome, respectively. The nutrition support clinician should be aware of patients who may be at risk for TD. Risk factors include those patients with malnutrition due to 1 or more nutrition-related etiologies: decreased nutrient intake, increased nutrient losses, or impaired nutrient absorption. Clinical scenarios such as unexplained heart failure or lactic acidosis, renal failure with dialysis, alcoholism, starvation, hyperemesis gravidarum, or bariatric surgery may increase the risk for TD. Patients who are critically ill and require nutrition support may also be at risk for TD, especially those who are given intravenous dextrose void of thiamin repletion. Furthermore, understanding thiamin's role as a potential therapeutic agent for diabetes, some inborn errors of metabolism, and neurodegenerative diseases warrants further research. This tutorial describes the absorption, digestion, and metabolism of thiamin. Issues pertaining to thiamin in clinical practice will be described, and evidence-based practice suggestions for the prevention and treatment of TD will be discussed.

Thiamine Deficiency-Mediated Brain Mitochondrial Pathology in Alaskan Huskies with Mutation in SLC19A3.1

Alaskan Husky encephalopathy (AHE(1) ) is a fatal brain disease associated with a mutation in SLC19A3.1 (c.624insTTGC, c.625C>A). This gene encodes for a thiamine transporter 2 with a predominately (CNS) central nervous system distribution. Considering that brain is particularly vulnerable to thiamine deficiency because of its reliance on thiamine pyrophosphate (TPP)-dependent metabolic pathways involved in energy metabolism and neurotransmitter synthesis, we characterized the impact of this mutation on thiamine status, brain bioenergetics and the contribution of oxidative stress to this phenotype. In silico modeling of the mutated transporter indicated a significant loss of alpha-helices resulting in a more open protein structure suggesting an impaired thiamine transport ability. The cerebral cortex and thalamus of affected dogs were severely deficient in TPP-dependent enzymes accompanied by decreases in mitochondrial mass and oxidative phosphorylation (OXPHOS) capacity, and increases in oxidative stress. These results along with the behavioral and pathological findings indicate that the phenotype associated with AHE is consistent with a brain-specific thiamine deficiency, leading to brain mitochondrial dysfunction and increased oxidative stress. While some of the biochemical deficits, neurobehavior and affected brain areas in AHE were shared by Wernicke's and Korsakoff's syndromes, several differences were noted likely arising from a tissue-specific vs. that from a whole-body thiamine deficiency.

Thiamine nutritional status and depressive symptoms are inversely associated among older Chinese adults

Thiamine has been hypothesized to play an important role in mental health; however, few studies have investigated the association between thiamine nutritional status and depression in the general population. Concentrations of free thiamine and its phosphate esters [thiamine monophosphate (TMP) and thiamine diphosphate (TDP)] in erythrocytes were measured by HPLC among 1587 Chinese men and women aged 50-70 y. The presence of depressive symptoms was defined as a Center for Epidemiological Studies Depression Scale score of ≥16. The median erythrocyte concentration (nmol/L) was 3.73 for free thiamine, 3.74 for TMP, and 169 for TDP. The overall prevalence of depressive symptoms was 11.3%. Lower concentrations of all 3 erythrocyte thiamine biomarkers were monotonically associated with a higher prevalence of depressive symptoms: the multivariable adjusted ORs comparing the lowest with the highest quartiles were 2.97 (95% CI = 1.87, 4.72; P-trend < 0.001) for free thiamine, 3.46 (95% CI = 1.99, 6.02; P-trend < 0.001) for TMP, and 1.98 (95% CI = 1.22, 3.21; P-trend = 0.002) for TDP. In conclusion, poorer thiamine nutritional status and higher odds of depressive symptoms were associated among older Chinese adults. This finding should be further investigated in prospective or interventional studies.

Nutrition and alcoholic encephalopathies

An assessment has been made of metabolic factors possibly causing or contributing to the brain damage associated with chronic alcoholism, especially thiamin lack or disturbance of amino acid metabolism. Abnormalities in the thiamin-dependent enzyme, transketolase, provide evidence of a high incidence of thiamin deficiency as well as of disturbed thiamin metabolism in chronic alcoholics, which are likely to be caused by reduced vitamin intake as well as impaired absorption. A grossly disturbed pattern of amino acids in the blood of patients undergoing treatment for alcohol withdrawal syndromes is likely to be caused by loss of hepatic function and may well aggravate brain damage caused by B group vitamin deficiency. A hypothesis is proposed of how chronic thiamin lack can lead to brain damage.

Determination of thiamine by high-performance liquid chromatography

High-performance liquid chromatographic methods for the determination of thiamine (vitamin B1) in foodstuffs or biological tissues and fluids are outlined and discussed. The methods are often similar and interchangeable, sample extraction and clean up procedures being the major difference. Most of the methods use either ultraviolet or fluorescence detection. Fluorescence detection requires either precolumn or postcolumn oxidation of thiamine to thiochrome. A number of methods are recommended and problems with standardization are emphasized.

Properties and functions of the thiamin diphosphate dependent enzyme transketolase

This review highlights recent research on the properties and functions of the enzyme transketolase, which requires thiamin diphosphate and a divalent metal ion for its activity. The transketolase-catalysed reaction is part of the pentose phosphate pathway, where transketolase appears to control the non-oxidative branch of this pathway, although the overall flux of labelled substrates remains controversial. Yeast transketolase is one of several thiamin diphosphate dependent enzymes whose three-dimensional structures have been determined. Together with mutational analysis these structural data have led to detailed understanding of thiamin diphosphate catalysed reactions. In the homodimer transketolase the two catalytic sites, where dihydroxyethyl groups are transferred from ketose donors to aldose acceptors, are formed at the interface between the two subunits, where the thiazole and pyrimidine rings of thiamin diphosphate are bound. Transketolase is ubiquitous and more than 30 full-length sequences are known. The encoded protein sequences contain two motifs of high homology; one common to all thiamin diphosphate-dependent enzymes and the other a unique transketolase motif. All characterised transketolases have similar kinetic and physical properties, but the mammalian enzymes are more selective in substrate utilisation than the nonmammalian representatives. Since products of the transketolase-catalysed reaction serve as precursors for a number of synthetic compounds this enzyme has been exploited for industrial applications. Putative mutant forms of transketolase, once believed to predispose to disease, have not stood up to scrutiny. However, a modification of transketolase is a marker for Alzheimer's disease, and transketolase activity in erythrocytes is a measure of thiamin nutrition. The cornea contains a particularly high transketolase concentration, consistent with the proposal that pentose phosphate pathway activity has a role in the removal of light-generated radicals.

Alcoholism and dementia

This article reviews epidemiological, neurological, cognitive, and imaging data on alcohol-induced dementia. Recent studies indicate that "heavy alcohol use" (variously defined) is a contributing factor in 21-24% of cases of dementia. Research difficulties include lack of positive diagnostic criteria, few post-mortem studies, and no accepted pathological mechanism. Sulcal widening and ventricular enlargement (occasionally reversible) are the strongest findings in patients with alcohol-induced dementia. There is evidence for peripheral neuropathy, ataxia, sparing of language, and improved prognosis when patients with alcohol-induced dementia are compared to other dements. Case examples, etiologic theories, and recommendations for research, training, and clinical practice are included.

Comparison of erythrocyte transketolase activity with thiamine and thiamine phosphate ester levels in chronic alcoholic patients

The effect of chronic alcoholism on biochemical evaluation of thiamine status was studied by the concomitant determination of erythrocyte transketolase (ETK) activity, its relative increase by in vitro addition of thiamine diphosphate (TDP effect) and the direct measurement of thiamine and its phosphate esters by high performance liquid chromatography. Thirty-eight percent of alcoholic subjects showed a thiamine deficiency with decreased thiamine diphosphate concentrations compared with healthy subjects (90.8 +/- 25.7 nmol/l vs. 176 +/- 28.0 nmol/l, respectively, mean +/- S.D., P < 0.001). Thiamine diphosphate concentrations were highly correlated with total thiamine concentrations and TDP effect (respectively r = 0.99 and 0.79, n = 85, P < 0.001). No abnormality in thiamine phosphorylation related to chronic alcoholism was noted. Finally, 47% of these deficient alcoholic patients had normal ETK activity. We concluded that, if indirect evaluation of thiamine status is to be chosen, the determination of ETK activity should be associated with TDP effect since the latter has been shown to be highly linked to total thiamine and thiamine diphosphate in erythrocytes. Furthermore, the direct measurement of thiamine and its phosphate esters was a more sensitive and specific index of thiamine nutrition.

An enzymatic and immunochemical analysis of transketolase in fibroblasts from Wernicke-Korsakoff syndrome

Transketolase in cultured skin fibroblasts from three patients with Wernicke-Korsakoff syndrome (GM7504, 7505 and 7506) and matched controls was analyzed enzymatically and immunochemically with specific antisera generated against transketolase purified from human liver or red blood cells. The transketolase activity decreased by 45% in fibroblasts from the three Wernicke-Korsakoff patients, when compared to the activity in control cells. On immunoblots after SDS-PAGE, fibroblasts from the Wernicke-Korsakoff patients exhibited a 69-kDa species, a size similar to that of normal transketolase. The level of immunoreactivity was similar in the patient and control cells. The immunoblots of isoelectric focusing gels showed a major species of pI 8.6 with additional minor bands. However, the isoelectric focusing pattern of transketolase from the Wernicke-Korsakoff patients was also found in the majority of the control fibroblasts. Thus transketolase in fibroblasts from these Wernicke-Korsakoff patients is catalytically defective, but appears to be immunochemically normal.

Nucleotide and predicted amino acid sequence of a cDNA clone encoding part of human transketolase

Transketolase is a key enzyme in the pentose-phosphate pathway which has been implicated in the latent human genetic disease, Wernicke-Korsakoff syndrome. Here we report the cloning and partial characterisation of the coding sequences encoding human transketolase from a human brain cDNA library. The library was screened with oligonucleotide probes based on the amino acid sequence of proteolytic fragments of the purified protein. Northern blots showed that the transketolase mRNA is approximately 2.2 kb, close to the minimum expected, of which approximately 60% was represented in the largest cDNA clone. Sequence analysis of the transketolase coding sequences reveals a number of homologies with related enzymes from other species.

No transketolase abnormalities in Wernicke-Korsakoff patients

Transketolase isoenzyme patterns of Wernicke-Korsakoff patients, relatives, alcoholics and controls, obtained by isoelectric focusing of purified erythrocyte transketolase, were all identical. After a series of investigations published by several authors little evidence remains to support the hypothesis of an inborn transketolase abnormality in Wernicke-Korsakoff patients.

Analysis of transketolase and identification of an enzyme variant in human leukocytes

Human leukocyte transketolase of fresh cell extracts has been analyzed by isoelectrofocusing on agarose gels (pH 3-10). The enzyme was then transblotted on nitrocellulose and detected with specific anti-transketolase IgG coupled to an avidin/biotin-immunoperoxidase system. Each sample yielded multiple enzyme forms, within a pI range of about 7.4-8.4. Transketolase profile, however, was not identical in all extracts. There are two mainly distinct patterns, showing qualitative and quantitative differences: a standard profile, which is predominant, and a variant, found in three unrelated subjects out of the two hundred and twenty. Standard and variant enzyme have similar Km values for ribose 5-P and xylulose 5-P and the same mobility on SDS-PAGE.

Interactions with hemoglobin: a source of error in measurements of transketolase activity in hemolysates

Measurements of the activity of transketolase in human erythrocyte lysates by an assay coupled to NADH oxidation indicate that interactions of assay substrates with hemoglobin can give rise to overestimations of transketolase activity. Three potential sources of error are identified. Thus, in lysates containing methemoglobin, NADH oxidation can be due firstly to methemoglobin reductase activity or secondly to the monooxygenase activity of methemoglobin, for which the substrate can be ribose 5-phosphate, a substrate also of transketolase. Thirdly, the addition of high concentrations of the transketolase cofactor, TDP, to an insufficiently buffered reaction mixture can cause the aggregation and precipitation of hemoglobin: a phenomenon that may be misconstrued as an enhanced increase in absorbance at 340 nm and hence as additional transketolase activity. Although the present study concentrates on these potential artefacts in assays of transketolase activity, the findings may well be relevant to the measurement of other enzyme activities in hemolysates by procedures based ultimately on the rate of consumption or production of NAD(P)H.

Transketolase from human leukocytes. Isolation, properties and induction of polyclonal antibodies

Transketolase has been purified for the first time from human leukocytes, according to a new procedure which consists of three conventional steps. The enzyme was finally detached from CM-cellulose by specific elution with a D-xylulose-5-phosphate/D-ribose-5-phosphate mixture and the isolated product exhibited a specific activity of about 10 units/mg protein at 37 degrees C. Transketolase preparations are contamination-free, except for a slight residual activity of phosphohexose isomerase. Kinetic constants for D-xylulose 5-phosphate and D-ribose 5-phosphate were found to be 0.19 mM and 0.63 mM, respectively. Pure transketolase migrates on SDS/PAGE as a single band, with a molecular mass of about 66 kDa. The isoelectrophoretic heterogeneity of transketolase was assessed either by activity staining or immunovisualization with anti-transketolase antisera, previously induced in rabbits. These techniques yielded two practically overlapping patterns consisting of 6-8 distinct bands within a pI range of 6.5-8.5. Both pure and crude transketolase preparations showed a similar heterogeneous profile, thus confirming the stability of the enzyme throughout purification. The occurrence of multiple enzyme forms in fresh human white cells has also been established by the analysis of transketolase in isolated populations of either lymphocytes or polymorphonuclear leukocytes, from individual healthy subjects.

The evaluation of erythrocyte thiamin diphosphate as an indicator of thiamin status in man, and its comparison with erythrocyte transketolase activity measurements

HPLC measurement of the major physiological form of thiamin, thiamin diphosphate, in erythrocytes (ETDP) has been assessed as an indicator of thiamin status and compared with erythrocyte transketolase activity (ETKA) before and after activation with exogenous thiamin diphosphate (TDP effect). The comparison was made by following the response of the parameters to incubation of erythrocytes with thiamin and by measurements in alcoholic, elderly and student groups. All parameters were responsive to the thiamin content of their environment, but ETDP was at least as sensitive as TDP effect and more sensitive than ETKA in reflecting thiamin uptake and utilisation by erythrocytes. There was a better correlation between ETDP and ETKA than between ETDP and TDP effect. All the groups showed a significant positive correlation between ETDP and ETKA, but only the elderly and the alcoholic groups showed a significant negative correlation between ETDP and TDP effect. The lack of correlation between ETDP and TDP effect in the student group may be due to the relative imprecision of TDP effect measurements at the lower end of the reference range. ETDP is more stable than ETKA in frozen erythrocytes, is easier to standardise and is not affected by various factors which can influence the enzyme assay. Measurement of ETDP is, therefore, recommended for first line assessment of thiamin status.

Isolation of transketolase from human erythrocytes

Transketolase was isolated from human red blood cells with over 6,200 fold purification by a new method. The stepwise procedure for the isolation of the enzyme from erythrocyte hemolysate included the use of ethanol/chloroform precipitation, chromatography on hydroxyapatite and finally, affinity adsorption on carboxymethyl-cellulose. The molecular weight of erythrocyte transketolase, as determined by polyacrylamide gel electrophoresis, appeared to be about 140,000. The pH optimum for activity was between 7.6 and 7.8 and the optimum temperature for activity was 50 degrees C. The Km values for xylulose-5-phosphate, ribose-5-phosphate and fructose-6-phosphate were 2.0 x 10(-4) M, 3.2 x 10(-4) M and 2.0 x 10(-3) M, respectively.

Rat brain apotransketolase: activation and inactivation

Kinetic analysis of the combination of rat brain apotransketolase with thiamine diphosphate suggested that the enzyme exists in more than one form. One part of the apoenzyme reacted rapidly with thiamine diphosphate to reconstitute the holoenzyme, but another part appeared to combine only relatively slowly. In addition, an apparently irreversible further change took place, the apoenzyme being converted progressively to a form which apparently could not be activated by thiamine diphosphate. The relative proportions of the three forms i.e., that reacting rapidly, slowly, or not at all with thiamine diphosphate, were a function of the duration and conditions of storage, with the proportion of the apoenzyme form which reacted rapidly with thiamine diphosphate decreasing progressively. The findings reported here provide a possible explanation for problems various workers have encountered in attempting to evaluate Michaelis constants for the reaction of thiamine diphosphate with apotransketolase.

Western blotting assay of transketolase concentration in human hemolysates

Using a rabbit anti-human transketolase antiserum and Western blotting we can determine nanogram amounts of transketolase in human hemolysates quantitatively. Transketolase concentration in 18 apparently healthy subjects was 55.7 +/- 12.1 micrograms/g Hb (mean +/- SD). Transketolase concentration correlated positively with the enzyme activity both with and without in vitro addition of thiamin pyrophosphate. However, the former had a closer correlation (r = 0.8418, P less than 0.001) than the latter (r = 0.6703, P less than 0.01). A heavy drinker with an extremely low transketolase activity had proportionally low concentration to the activity. These results indicate that transketolase in hemolysates, whether it is holoenzyme or apoenzyme activated in vitro, has an identical specific activity among all subjects studied and that the reduced activity of transketolase in alcoholics is due to the reduced content of the enzyme protein. This method is applicable to study the dynamics and the abnormality of apotransketolase in human hemolysates.

The activation of red blood cell transketolase in groups of patients especially at risk from thiamin deficiency

Erythrocyte transketolase activation by thiamin diphosphate has been studied in elderly patients with moderate or severe chronic dementia, acute alcoholic admissions and chronic alcoholics with evidence of brain damage, mostly of the Wernicke-Korsakoff type. Significantly more patients in each group than controls showed abnormal activation of transketolase, not only by 0.3 mM thiamin diphosphate (TDP) but also in further activation by increase to 3 mM. This indicated the presence in a proportion of the alcoholic and the demented patients of an abnormal enzyme variant, similar to that previously found in vitro. The modified transketolase activation test may warn not only of marginal thiamin deficiency but also independently, of susceptibility to brain damage in patients at risk.

Human erythrocyte transketolase: no evidence for variants

Using isoelectric focusing of human erythrocyte transketolase, the isoenzyme pattern described recently (Kaczmarek and Nixon, 1983) was reexamined. Seven bands having pI values of 7.4-8.4 were common to the central part of the transketolase isoenzyme pattern in 63 healthy subjects investigated and were definitely reproduced, whereas four additional marginal bands (pI values of 7.2, 7.3, 8.6 and 8.8) were found with varying intensities in part of the samples and could not always be reproduced. We conclude that the method used does not permit the distinction of transketolase variants, that would allow to postulate a genetic polymorphism, based only on variation of the marginal bands of the pattern.

Measurement of Michaelis constant for human erythrocyte transketolase and thiamin diphosphate

Human erythrocyte transketolase could be resolved from thiamin diphosphate (TDP) by acidification of the ammonium sulfate precipitate to pH 3.5, but not by other tested procedures. Resolution was 98% by chemical measurement of residual thiamin and 95% by residual enzyme activity. Reconstitution of the resolved preparation by incubation with TDP was dependent upon TDP concentration, duration, temperature, and the presence of dithiothreitol. At low TDP concentrations, 1 h was required for maximum activation; kinetic analysis then yielded an apparent Km value for TDP of 65 nM (SD 14 nM) from 100 erythrocyte lysates and similar values for reconstituted resolved preparations previously purified 400-fold and 10,000-fold. Velocity data obtained by transketolase assays in which the TDP was added to resolved preparations simultaneously with substrates yielded an apparent Km value for TDP of 2.3 microM (SD 1.6 microM) from 114 erythrocyte lysates and similar values for purified preparations. The recovery of activity following resolution and reconstitution ranged from 21 to 60% from lysates and 38 to 70% from purified preparations. Residual ammonium sulfate up to 4.9 mM decreased the apparent Km value for TDP, while a concentration of 11.3 mM increased the value in a manner competitive with TDP and with an apparent Ki value of 2.3 mM. The spectrophotometric assay of transketolase activity was greatly affected by storage of frozen solutions of the substrate ribose 5-phosphate.

Reduced stability of rat brain transketolase after conversion to the apo form

The stability of rat brain transketolase, whether measured at 37 or 0 degree C, was reduced after conversion to the apo form by removal of thiamine diphosphate, as shown by a decline in the activity recovered when assayed in the presence of thiamine diphosphate. Both the shape of the breakdown curve and the failure to recover the full activity, even after incubation with thiamine diphosphate, showed that the breakdown of the apotransketolase was complex. The initial rate of breakdown of the apoenzyme was sharply pH dependent, being minimal at 37 degrees C at a pH value of 7.6, close to that likely to exist in vivo. The rate rose sharply with deviation of the pH in either direction. The stability of the enzyme on storage at 0 degree C showed a similar pattern of pH dependence, provided that allowance is made for temperature effects on dissociation constants. These findings provide further support for the hypothesis that differences in brain transketolase may play a part in the etiology of Wernicke-Korsakoff's syndrome.

Immunoaffinity purification of rat liver transketolase: evidence for multiple forms of the enzyme

Rat liver transketolase (TK) has been purified, in a single step, by immunoaffinity chromatography on specific TK antibodies covalently linked to Sepharose 4B. The procedure described also involves the raising and isolation of rabbit TK antibodies to the conventionally purified enzyme [F. Paoletti (1983) Arch. Biochem. Biophys. 222, 489-496]. Affinity chromatography allows a 100-fold purification of TK from the cell cytosol and a recovery of about 70% of the original activity. The TK isolated has a specific activity of 2.7-3.2 at 25 degrees C and migrates as a single band on polyacrylamide gel electrophoresis at pH 9.1. Multiple forms of the enzyme, with distinct pI values in the range 7-8, have been detected in purified preparations by means of analytical isoelectric focusing and staining for TK. No addition of either Mg2+ or thiamine pyrophosphate is required for the activity of the enzyme which, in the native form, exhibits a molecular weight of about 139,000. Two moles of thiamine pyrophosphate can be resolved for each mole of enzyme. Affinity TK preparations are virtually free of glyceraldehyde-3-phosphate dehydrogenase, pentose-phosphate epimerase, and isomerase, although slight contamination by phosphohexose isomerase may occur.

Changes in erythrocyte transketolase activity and the thiamine pyrophosphate effect during storage of blood

Whole blood and washed erythrocytes from nutritionally normal and abnormal elderly patients were stored at room temperature, 4 degrees C and -20 degrees C for up to 14 days. In both groups, and under all storage conditions, the erythrocyte transketolase (ETK) activity and the thiamine pyrophosphate (TPP) effect decreased with time of storage. The ETK activity for specimens stored at -20 degrees C decreased significantly by day 14 (P less than 0.05). The TPP effect in specimens stored at -20 degrees C decreased significantly in the nutritionally abnormal group at 4 days (P less than 0.05) and in the nutritionally normal group by day 14 (P less than 0.05). These significant changes in ETK activity and TPP effect with storage can lead to misleading interpretation of thiamine nutritional status.

An erythrocyte transketolase isoenzyme pattern associated with the Wernicke-Korsakoff syndrome

Two techniques were used to seek variants of human erythrocyte transketolase and to test for any association of the Wernicke-Korsakoff syndrome, a thiamin-deficiency disease, with a particular variant of this thiamin-dependent enzyme. Apparent Km values for the cofactor thiamin diphosphate were similar for patients and controls. However, isoelectric focussing separated erythrocyte transketolase into different isoenzymes characterized by pI values in the range 6.6-9.2. Six distinct patterns of isoenzymes were found in thirty-six healthy control subjects. The isoenzyme pattern for thirty-nine out of forty-two patients suffering from the Wernicke-Korsakoff syndrome was identical to a pattern found in only eight of thirty-six control subjects, a highly significant association (P less than 0.001). This association suggests that a variant transketolase and thiamin deficiency together contribute to the pathogenesis of the brain damage of the Wernicke-Korsakoff syndrome by some mechanism independent of apparent Km values for thiamin diphosphate.