A protecting group-free synthesis of deazathiamine: a step toward inhibitor design

The discovery of 3-deazathiamine diphosphate (deazaThDP) as a potent inhibitor analog of the cofactor thiamine diphosphate (ThDP) has highlighted the need for an efficient and scalable synthesis of deazaThDP. Such a method would facilitate development of analogs with the ability to inhibit individual ThDP-dependent enzymes selectively. Toward the goal of developing selective inhibitors of the mycobacterial enzyme 2-hydroxy-3-oxoadipate synthase (HOAS), we report an improved synthesis of deazaThDP without use of protecting groups. Tribromo-3-methylthiophene served as a versatile starting material whose selective functionalization permitted access to deazaThDP in five steps, with potential to make other analogs accessible in substantial amounts.

Dihydroxyacetone synthase from a methanol-utilizing carboxydobacterium, Acinetobacter sp. strain JC1 DSM 3803

Acinetobacter sp. strain JC1 DSM 3803, a carboxydobacterium, grown on methanol was found to show dihydroxyacetone synthase, dihydroxyacetone kinase, and ribulose 1,5-bisphosphate carboxylase, but no hydroxypyruvate reductase and very low hexulose 6-phosphate synthase, activities. The dihydroxyacetone synthase was found to be expressed earlier than the ribulose 1,5-bisphosphate carboxylase. The dihydroxyacetone synthase was purified 19-fold in eight steps to homogeneity, with a yield of 9%. The final specific activity of the purified enzyme was 1.12 micromol of NADH oxidized per min per mg of protein. The molecular weight of the native enzyme was determined to be 140,000. Sodium dodecyl sulfate-gel electrophoresis revealed a subunit of molecular weight 73,000. The optimum temperature and pH were 30 degrees C and 7.0, respectively. The enzyme was inactivated very rapidly at 70 degrees C. The enzyme required Mg2+ and thiamine pyrophosphate for maximal activity. Xylulose 5-phosphate was found to be the best substrate when formaldehyde was used as a glycoaldehyde acceptor. Erythrose 4-phosphate, glycolaldehyde, and formaldehyde were found to act as excellent substrates when xylulose 5-phosphate was used as a glycoaldehyde donor. The Kms for formaldehyde and xylulose 5-phosphate were 1.86 mM and 33.3 microM, respectively. The enzyme produced dihydroxyacetone from formaldehyde and xylulose 5-phosphate. The enzyme was found to be expressed only in cells grown on methanol and shared no immunological properties with the yeast dihydroxyacetone synthase.

The absence of Pmp47, a putative yeast peroxisomal transporter, causes a defect in transport and folding of a specific matrix enzyme

Candida boidinii Pmp47, an integral peroxisomal membrane protein, belongs to a family of mitochondrial solute transporters (e.g., ATP/ADP exchanger), and is the only known peroxisomal member of this family. However, its physiological and biochemical functions have been unrevealed because of the difficulties in the molecular genetics of C. boidinii. In this study, we first isolated the PMP47 gene, which was the single gene encoding for Pmp47 in a gene-engineerable strain S2 of C. boidinii. Sequence analysis revealed that it was very similar to PMP47A and PMP47B genes from a polyploidal C. Boidinii strain (ATCC32195). Next, the PMP47 gene was disrupted and the disruption strain (pmp47delta) was analyzed. Depletion of PMP47 from strain S2 resulted in a retarded growth on oleate and a complete loss of growth on methanol. Both growth substrates require peroxisomal metabolism. EM observations revealed the presence of peroxisomes in methanol- and oleate-induced cells of pmp47delta, but in reduced numbers, and the presence of material of high electron density in the cytoplasm in both cases. Methanol-induced cells of pmp47delta were investigated in detail. The activity of one of the methanol-induced peroxisome matrix enzymes, dihydroxyacetone synthase (DHAS), was not detected in pmp47delta. Further biochemical and immunocytochemical experiments revealed that the DHAS protein aggregated in the cytoplasm as an inclusion body, while two other peroxisome matrix enzymes, alcohol oxidase (AOD) and catalase, were active and found in peroxisomes. Two peroxisome-deficient mutants, strains M6 and M13 (described in previous studies), retained DHAS activity although it was mislocalized to the cytoplasm and the nucleus. We disrupted PMP47 in these peroxisome-deficient mutants. In both strains, M6-pmp47delta and M13-pmp47delta, DHAS was enzymatically active and was located in the cytoplasm and the nucleus. We suggest that an unknown small molecule, which PMP47 transports, is necessary for the folding or the translocation machinery of DHAS within peroxisomes. Pmp47 does not catalyze folding directly because active DHAS is observed in the M6-pmp47delta and M13-pmp47delta strains. Since both AOD and DHAS have the PTS1 motif sequences at their carboxyl terminal, our results first show that depletion of Pmp47 could dissect the peroxisomal import pathway (PTS1 pathway) of these proteins.

Characterization of peroxisome-deficient mutants of Hansenula polymorpha

In the methylotrophic yeast Hansenula polymorpha, approximately 25% of all methanol-utilization-defective (Mut-) mutants are affected in genes required for peroxisome biogenesis (PER genes). Previously, we reported that one group of per mutants, termed Pim-, are characterized by the presence of a few small peroxisomes with the bulk of peroxisomal enzymes located in the cytosol. Here, we describe a second major group of per mutants that were observed to be devoid of any peroxisome-like structure (Per-). In each Per- mutant, the peroxisomal methanol-pathway enzymes alcohol oxidase, catalase and dihydroxyacetone synthase were present and active but located in the cytosol. Together, the Pim- and Per- mutant collections involved mutations in 14 different PER genes. Two of the genes, PER5 and PER7, were represented by both dominant-negative and recessive alleles. Diploids resulting from crosses of dominant per strains and wild-type H. polymorpha were Mut- and harbored peroxisomes with abnormal morphology. This is the first report of dominant-negative mutations affecting peroxisome biogenesis.

Oxalate metabolism in magnesium-deficient rats

Male weanling rats were maintained on magnesium-deficient diet for 30 d and compared with pair-fed control rats fed magnesium-supplemented diet. Magnesium deficiency led to slow growth and finally to a significant decrease in body weight (P < 0.001) accompanied by a significant hypomagnesaemia, hypomagnesuria and hyperoxaluria (P < 0.001 in each case) in experimental rats as compared to the control rats. Magnesium deficiency altered the glyoxylate metabolism in the liver and kidney mitochondria by significantly decreasing glyoxylate oxidation (by 26 per cent in liver and 17 per cent in kidney) and activity of alpha-ketoglutarate:glyoxylate carboligase enzyme (by 35 per cent in liver and 27 per cent in kidney) in the experimental animals. A significant increase in the specific activities of glycolic acid oxidase (P < 0.001) and glycolic acid dehydrogenase (P < 0.01) and a significant decrease in alanine transaminase (P < 0.01) was also observed in magnesium-deficient rats. No change in liver and kidney lactate dehydrogenase was observed. Thus magnesium deficiency in rats leads to accumulation of glyoxylate in the tissues, a part of which is converted into oxalate, thereby promoting hyperoxaluria.

Targeting sequences of the two major peroxisomal proteins in the methylotrophic yeast Hansenula polymorpha

Dihydroxyacetone synthase (DAS) and methanol oxidase (MOX) are the major enzyme constituents of the peroxisomal matrix in the methylotrophic yeast Hansenula polymorpha when grown on methanol as a sole carbon source. In order to characterize their topogenic signals the localization of truncated polypeptides and hybrid proteins was analysed in transformed yeast cells by subcellular fractionation and electron microscopy. The C-terminal part of DAS, when fused to the bacterial beta-lactamase or mouse dihydrofolate reductase, directed these hybrid polypeptides to the peroxisome compartment. The targeting signal was further delimited to the extreme C-terminus, comprising the sequence N-K-L-COOH, similar to the recently identified and widely distributed peroxisomal targeting signal (PTS) S-K-L-COOH in firefly luciferase. By an identical approach, the extreme C-terminus of MOX, comprising the tripeptide A-R-F-COOH, was shown to be the PTS of this protein. Furthermore, on fusion of a C-terminal sequence from firefly luciferase including the PTS, beta-lactamase was also imported into the peroxisomes of H. polymorpha. We conclude that, besides the conserved PTS (or described variants), other amino acid sequences with this function have evolved in nature.

DNA sequence of the yeast transketolase gene

Transketolase (EC 2.2.1.1) is the enzyme that, together with aldolase, forms a reversible link between the glycolytic and pentose phosphate pathways. We have cloned and sequenced the transketolase gene from yeast (Saccharomyces cerevisiae). This is the first transketolase gene of the pentose phosphate shunt to be sequenced from any source. The molecular mass of the proposed translated protein is 73,976 daltons, in good agreement with the observed molecular mass of about 75,000 daltons. The 5'-nontranslated region of the gene is similar to other yeast genes. There is no evidence of 5'-splice junctions or branch points in the sequence. The 3'-nontranslated region contains the polyadenylation signal (AATAAA), 80 base pairs downstream from the termination codon. A high degree of homology is found between yeast transketolase and dihydroxyacetone synthase (formaldehyde transketolase) from the yeast Hansenula polymorpha. The overall sequence identity between these two proteins is 37%, with four regions of much greater similarity. The regions from amino acid residues 98-131, 157-182, 410-433, and 474-489 have sequence identities of 74%, 66%, 83%, and 82%, respectively. One of these regions (157-182) includes a possible thiamin pyrophosphate (TPP) binding domain, and another (410-433) may contain the catalytic domain.

Methanol metabolism in a peroxisome-deficient mutant of Hansenula polymorpha: a physiological study

We have studied methanol-utilization in a peroxisome-deficient (PER) mutant of Hansenula polymorpha. In spite of the fact that in carbon-limited chemostat cultures under induced conditions the enzymes involved in methanol metabolism were present at wild-type (WT) levels, this mutant is unable to grow on methanol as a sole carbon and energy source. Addition of methanol to glucose-limited (SR = 12.5 mM) chemostat cultures of the PER mutant only resulted in an increase in yield when small amounts were used (up to 22.5 mM). At increasing amounts however, a gradual decrease in cell density was observed which, at 80 mM methanol in the feed, had dropped below the original value of the glucose-limited culture. This reduction in yield was not observed when increasing amounts of formate instead of methanol were used as supplements for the glucose-limited mutant culture and also not in WT cells, used as control in these experiments. The effect of addition of methanol to a glucose-limited PER culture was also studied in the transient state during adaptation of the cells to methanol. The enzyme patterns obtained suggested that the ultimate decrease in yield observed at enhanced methanol concentrations was due to an inefficient methanol-metabolism as a consequence of the absence of peroxisomes. The absence of intact peroxisomes results in two major problems namely i) in H2O2-metabolism, which most probably is no longer mediated by catalase and ii) the inability of the cell to control the fluxes of formaldehyde, generated from methanol. The energetic consequences of this metabolism, compared to the WT situation with intact peroxisomes, are discussed.

Investigations into the effect of glyoxylate decarboxylation and transamination on oxalate formation in the rat

The decarboxylation and transamination reactions of glyoxylate, which divert this precursor from oxalate formation, have been investigated. Decarboxylation of glyoxylate is synergistic with 2-oxoglutarate and catalysed by 2-oxoglutarate:glyoxylate carboligase which co-chromatographs with the 2-oxoglutarate dehydrogenase complex. The activity is located in the mitochondrial fraction and is probably due to the E1 subunit of the complex. A greater amount of decarboxylation occurs from 2-oxoglutarate than from glyoxylate but the presence of 2-oxoglutarate does not affect oxalate formation from glyoxylate. There is no oxalate formation from 2-oxoglutarate. Studies with rat liver homogenates showed that a number of amino acids can participate in glyoxylate transamination. However, using isolated rat hepatocytes, these reactions did not have a significant effect on oxalate formation from glyoxylate with the exception of cysteine which caused an 80% reduction in oxalate formation. Investigation of this inhibition indicated that it was most likely due to the formation of a cysteine-glyoxylate adduct which makes glyoxylate unavailable for oxidation to oxalate. This cysteine inhibition of oxalate formation was also demonstrated in normal rats and rats made hyperoxaluric by injecting them with either glyoxylate or glycolate. The results indicate that sulphydryl compounds, which can have a therapeutic role as oxalate-lowering agents, may be able to be developed.

Peroxisomal assembly: membrane proliferation precedes the induction of the abundant matrix proteins in the methylotrophic yeast Candida boidinii

Peroxisomes are massively induced when methylotrophic yeasts are cultured in medium containing methanol. These organelles contain enzymes that catalyze the initial steps of methanol assimilation. In Candida boidinii, a methylotrophic yeast, the peroxisomal matrix (internal compartment) is composed almost exclusively of two proteins, alcohol oxidase and dihydroxyacetone synthase; catalase is present in much lower abundance. Monoclonal and polyclonal antibodies are available against peroxisomal matrix and membrane proteins. These were utilized to correlate the induction of specific proteins with the morphological changes occurring during peroxisomal proliferation. Cells cultured in glucose-containing medium contain two to five small microbodies, which are identifiable by catalase staining and immunoreactivity with a monoclonal antibody against PMP47, an integral peroxisomal membrane protein. Three stages of proliferation can be distinguished when cells are switched to methanol as the carbon source. (1) There is an early stage (within 1 h) in which several peroxisomes develop from a preexisting organelle. This is accompanied by an increase in catalase activity and an induction of PMP47, but no detectable induction of alcohol oxidase or dihydroxyacetone synthase is observed. (2) From 1 to 2.5 h there is further division of these microbodies until up to 30 small peroxisomes generally are present in each of one or two clusters per cell. Induction of alcohol oxidase, dihydroxyacetone synthase and PMP20, a protein that is distributed in the matrix and membrane, is detectable during this time. Serial sections reveal that some peroxisomes remain uninduced while others undergo proliferation. Such sections also show no obvious connections between peroxisomes within clusters.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosynthesis of the peroxisomal dihydroxyacetone synthase from Hansenula polymorpha in Saccharomyces cerevisiae induces growth but not proliferation of peroxisomes

The DAS gene of Hansenula polymorpha was expressed in Saccharomyces cerevisiae under the control of different promoters. The heterologously synthesized dihydroxyacetone synthase (DHAS), a peroxisomal enzyme in H. polymorpha, shows enzymatic activity in baker's yeast. The enzyme was imported into the peroxisomes of S. cerevisiae not only under the appropriate physiological conditions for peroxisome proliferation (oleic acid media), but also in glucose-grown cells where it induced the enlargement of the few peroxisomes present. This growth process was not accompanied by an increase in the number of microbodies, which suggests a separate control mechanism for peroxisomal proliferation.

Expression of the lacZ gene from two methanol-regulated promoters in Pichia pastoris

Two DNA fragments containing putative control regions regulating the expression of the alcohol oxidase (AOX) and dihydroxy-acetone synthase (DAS) genes from the methylotrophic yeast Pichia pastoris were used in the construction of vectors for the expression of the Escherichia coli lacZ gene. These vectors were transformed into P. pastoris host cells and employed in experiments to measure the control mechanisms employed by each promoter in the production of beta-galactosidase fusion products. Results in P. pastoris suggest that the processes used to regulate the expression of these gene fusions involve both repression/derepression and induction mechanisms. Expression of the AOX-lacZ and DAS-lacZ fusions was examined in Saccharomyces cerevisiae as well. Interestingly, beta-galactosidase was expressed in a regulated manner in the heterologous host.

Oxalate metabolism in thiamine-deficient rats

Male weanling rats were maintained on a thiamine-deficient diet for 4 weeks, and compared with ad libitum and pair-fed controls. Thiamine deficiency led to slow growth and finally a decrease in body weight. Liver and kidney weights of the deficient rats were low, but appropriate to the body weight. Thiamine deficiency also caused a significant decrease in erythrocyte transketolase levels. The decarboxylation of glyoxylate both via the glyoxylate oxidation cycle and alpha-ketoglutarate:glyoxylate (alpha-KG:GA) carboligase was significantly lower in the liver and kidney mitochondria, leading to accumulation of glyoxylate in the tissues and its excretion in the urine. Part of the accumulated glyoxylate is converted to oxalate, causing hyperoxaluria.

Biosynthesis of Rhizobium trifolii capsular polysaccharide: enzymatic transfer of pyruvate substitutions into lipid-bound saccharide intermediates

The activity of capsular polysaccharide pyruvyltransferase catalyzing the pyruvylation of acidic heteropolysaccharide was measured in Rhizobium trifolii 843 and 0403 rif. This enzyme activity was determined with EDTA-treated cells, uridine diphosphate-sugar precursors, and phosphoenol [1-14C]pyruvate. Activity was measured by the incorporation of radioactivity into organic solvent-soluble glycoconjugates. Enzymatic pyruvylation of capsular polysaccharide occurred from phosphoenolpyruvate at the lipid-bound saccharide stage.

Mitochondrial damage and the subcellular distribution of 2-oxoglutarate:glyoxylate carboligase in normal human and rat liver and in the liver of a patient with primary hyperoxaluria type I

The subcellular distribution of 2-oxoglutarate:glyoxylate carboligase was investigated in a normal human liver, a liver from a patient with pyridoxine-resistant primary hyperoxaluria type I and rat livers subjected to various degrees and types of trauma. On continuous sucrose gradients most of the carboligase fractionated with a peak equilibrium density of 1.19-1.20 g/cm3 and paralleled the distribution of the major peaks of monoamine oxidase, glutamate dehydrogenase and cytochrome oxidase and can be considered to be mitochondrial. Various proportions of the carboligase and mitochondrial marker enzymes were found to be 'extramitochondrial' (at or near the top of the sucrose gradients), depending on the liver source and the severity of trauma to which they were subjected. Carboligase, monoamine oxidase (outer membrane marker) and glutamate dehydrogenase (matrix marker) were released from mitochondria by the homogenization and centrifugation procedures, to the extent of 19.9%, 32.4% and 11.5% respectively in hyperoxaluric liver, 12.5%, 17.9% and 8.2% in normal human liver and 3.0%, 4.9% and 3.8% in control rat liver. The proportion of extramitochondrial cytochrome oxidase (inner membrane marker) was virtually undetectable in both human and rat livers. However, sonication of rat liver homogenates or the addition of the detergent Triton X-100 caused a massive release of all four enzymes. The extramitochondrial carboligase was probably in the form of a free protein of very high molecular weight or aggregate, rather than associated with a mitochondrion-derived organelle. Subfractionation of a rat liver mitochondrial preparation indicated that most of the carboligase activity paralleled activities of 2-oxoglutarate decarboxylase, citrate synthase and glutamate dehydrogenase and was probably located in the matrix.(ABSTRACT TRUNCATED AT 250 WORDS)

Dihydroxyacetone synthase is an abundant constituent of the methanol-induced peroxisome of Candida boidinii

Methylotrophic yeasts induce large peroxisomes when grown on methanol. The recent ability to stabilize and isolate these peroxisomes at pH 5.5 has led to the demonstration that two polypeptides comprise the bulk of the peroxisome of Candida boidinii, alcohol oxidase, and a 79-kDa species, determined by sodium dodecyl sulfate-polyacrylamide electrophoresis (Goodman, J.M., Scott, C.W., Donahue, P.N., and Atherton, J.P. (1984) J. Biol. Chem. 259, 8485-8493). The 79-kDa peroxisomal protein is now identified as dihydroxyacetone synthase, the first enzyme in the assimilatory pathway of formaldehyde utilization. This identification is based on several criteria: The enzyme activity is mainly in a particulate fraction at pH 5.5 but not at pH 8.0. It copurifies with alcohol oxidase and catalase on sucrose gradients. The 79-kDa protein behaves as a 135,000-kDa dimer on gel filtration, similar to the published behavior of the enzyme. The specific activity of dihydroxyacetone synthase in the pure 79-kDa preparation (3.20 units/mg of protein) is close to that reported for the purified enzyme (3.88 units/mg of protein). Antibodies against dihydroxyacetone synthase were used to show that its synthesis, induction, and assembly are similar to that of alcohol oxidase. Neither contains a detectable cleaved leader sequence and both are assembled post-translationally. The localization of dihydroxyacetone synthase to the peroxisome may influence the regulation of the two pathways of formaldehyde utilization and may protect the cell from damage by formaldehyde.

Cloning and characterization of the DAS gene encoding the major methanol assimilatory enzyme from the methylotrophic yeast Hansenula polymorpha

A gene library from the methanol utilizing yeast Hansenula polymorpha, constructed in a lambda Charon4A vector, was used to clone the gene encoding a key methanol assimilating enzyme, dihydroxyacetone synthase (DHAS) by differential plaque hybridization. The nucleotide sequence of the 2106 bp structural gene and the 5' and 3' non-coding regions was determined. The deduced amino acid sequence of the protein is in agreement with the apparent molecular weight and amino acid composition of the purified protein. The codon bias is not so pronounced as in some Saccharomyces cerevisiae genes.

Sequential studies of oxalate dynamics in primary hyperoxaluria

We have measured the total plasma clearance, renal clearance and equilibrium distribution volume of [14C]oxalate, and the urinary oxalate excretion rate and plasma oxalate levels at approximately 6 months intervals for up to 2.5 years in five patients with primary hyperoxaluria. The renal clearance and distribution volumes of [99mTc]DTPA (diethylenetriaminepenta-acetate) were measured simultaneously to provide estimates of glomerular filtration rate (GFR) and extracellular fluid volume (ECF). The same measurements were made on each of five normal volunteers. Clearances and distribution volumes were measured with a modified single injection technique. The oxalate clearance was two to three times the simultaneously measured GFR in the patients and control subjects. The renal clearance of oxalate was less than the total plasma clearance in the patients. The oxalate distribution volume was approximately 1.5 times the ECF in both the patients and controls. Only small changes were observed over a 2.5 years period in these particular patients. The plasma oxalate concentration was derived from the urinary oxalate excretion rate and the plasma [14C]oxalate clearance. It was raised in the patients. The oxalate removal rate was derived from the total plasma clearance and the plasma oxalate concentration.

[Dihydroxyacetone synthase from the methanol-utilizing yeast Candida boidinii]

A procedure for purification of dihydroxyacetone synthase catalyzing the formation of dihydroxyacetone and glyceraldehyde 3-phosphate from formaldehyde and xylulose 5-phosphate has been developed. Using ion-exchangers with increasing affinity for dihydroxyacetone synthase, a homogenous preparation of the enzyme with specific activity of 2 u./mg has been obtained. The enzyme is made up of 2 subunits with m. w. of 76,000, contains thiamine pyrophosphate, requires Mg2+ for its activity and differs from yeast transketolase by substrate specificity and some other properties. The role of dihydroxyacetone synthase in metabolism of methanol-utilizing yeasts is discussed.

Simultaneous assay of dihydroxyacetone synthase and transketolase in a methylotrophic yeast grown in continuous culture. A cautionary note

The methylotrophic yeast Candida boidinii CBS 5777 was grown in continuous culture under carbon limitation on glucose, glucose plus methanol, and methanol as carbon and energy sources. During adaptation from glucose to methanol there was a rapid rise in the specific activities of triokinase, fructose-1,6-bisphosphatase and dihydroxyacetone synthase, which are key enzymes of the xylulose phosphate cycle of formaldehyde fixation. The specific activity of classical transketolase fell during this adaptation. Extracts from carbon-limited C. boidinii contained an enzyme which catalysed oxidation of NADH when some preparations or ribose 5-phosphate were added, which was not a transketolase. This enzyme activity was dependent on an impurity in such ribose 5-phosphate preparations and can be confused with transketolase activity.

The interrelation transketolase and dihydroxyacetone synthase activities in the methylotrophic yeast Candida boidinii

Crude extracts of Candida boidinii grown on glucose, xylose or ethanol gave single peaks of classical transketolase activity following chromatography, on columns of hydroxylapatite; the enzyme was heat-stable and showed no appreciable activity with formaldehyde as acceptor in place of ribose 5-phosphate. Extracts of methanol-grown cells showed two peaks of transketolase activity following chromatography on both hydroxylapatite and DEAE-cellulose. One peak was identified with that found for the cells grown on substrates other than methanol; the other peak showed dihydroxyacetone synthase activity in addition to transketolase activity. Both activities in the latter peak were very unstable and have been ascribed to one enzyme on the basis of identical rates of denaturation at all temperatures tested between 0 and 40 degrees C. It is suggested that this enzyme is a special transketolase synthesized only during methylotrophic growth of the yeast and in contrast to classical transketolase, is capable of using equally well either formaldehyde or ribose 5-phosphate as glycolaldehyde acceptor. A method based on heat treatment has been suggested for the simultaneous assay of both transketolases present in crude extracts of a methylotrophically grown yeast.

Thiamine deficiency and glyoxylic acid

The effect of thiamine deficiency on glyoxylic acid metabolism in mice and rats was investigated to determine whether the vitamin deficiency results in gross effects on glyoxylate levels via an alteration in the activity of alpha-ketoglutarate:glyoxylate carboligase. Thiamine-deprived or pyrithiamine-treated mice did not show a decreased oxidation of [1-14C]glyoxylate to respiratory CO2; there was some decrease in the conversion of [2-14C]glyoxylate into CO2 by pyrithiamine-treated mice, but not by thiamine-deprived animals. Dietary thiamine deprivation caused a decrease in carboligase levels in liver but no effect on levels in three brain regions. Pyrithiamine treatment had no significant effect on liver carboligase activities, but did decrease the levels in cerebrum, cerebellum and brainstem. Thiamine-deprived and pyrithiamine-treated mice showed decreased urinary glycolic acid excretion Glyoxylic acid excretion by thiamine-deprived rats was monitored in order to re-examine a previous report by another laboratory that glyoxyluria occurs under these conditions. Trace amounts of glyoxylate could be detected in the urine of rats fed thiamine-deficient diet for 3-5 weeks, but urinary glyoxylate was not detectable at later stages of thiamine deprivation. These results do not support a significant role for alpha-ketoglutarate:carboligase activity in the primary etiology of thiamine deficiency syndromes.