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PubMedDate not supplied

[Role of muscle pyruvate dehydrogenase histidine residues in thiamine pyrophosphate binding].

The interaction of diethylpyrocarbonate (DEP) with the pyruvate dehydrogenase component (PDH) isolated from the pyruvate dehydrogenase complex (EC 1.2.4.1) results in a modification of 3-5 histidine residues per mole of enzyme, which simultaneously decreases the enzyme activity. After PDH inhibilion by DEP in the presence of dithiothreitol almost complete reactivation (94%) under the effect of neutral hydroxylamine is observed. In the absence of SH-groups protection incomplete reactivation by hydroxylamine (79%) is found. In the latter case titration with 5,5-dithio--bis-(2-nitrobenzoic acid) in 8 M urea showed that the DEP-modified protein contains less quantity of SH groups (by 4-8) as compared to the native enzyme. It is assumed that the DEP-modified SH-groups are not responsible for the enzyme activity. The differential spectrum of the modified and native PDH showed no changes within the range of 260-300 nm. TPP in combination with Mg2+ (10(-3) M) protectes PDH from being inactivated by DEP. TPP (10(-2) M) reactivates PDH by 70% after its complete inhibition by DEP. Similar protective action is manifested by ATP, ADP and inorganic pyrophosphate in the presence of Mg2+. A kinetic study showed a competitive type of PDH inhibition by DEP with respect to TPP. it is concluded that the histidine residues of PDH are involved in TPP binding.

Catalysis↗
PubMed1992

Thiamin pyrophosphate binding mechanism and the function of the aminopyrimidine part.

Besides the pyrophosphate group, acting as the essential and primary binding function of TPP the N1-atom of the aminopyrimidine component functions as a second and also essential anchor to the protein component. Only if both of the contacts are formed the productive conformation of TPP within the active site of TPP enzymes is realized. A mechanism is proposed, which explains the results of our experiments with TPP-analogs.

Amines↗
PubMedDate not supplied

[Effect of oxygen, water and hydrophobic medium in model reactions of thiamine pyrophosphate].

Oxygen and water are inhibitors of acyloin and benzoin condensations. An intermediate paramagnetic compund is formed in the benzoin condensation catalyzed with 3-benzyl-4-methyl thiazolium chloride, 3,4-dimethyl thiazolium iodide, 3-benzyl-4,5-dimethyl thiazolium chloride, 3-methyl-4-phenyl thiazolium perchlorate and 3-methyl-4,5-diphenyl thiazolium perchlorate. The formation of benzoin in dimethyl sulphoxide, when the air oxygen is absent, is an irreversible reaction. The presence of hydrophobic solvent in the reaction medium provides more favourable conditions for benzoin condensation proceeding. The reaction mechanism is suggested.

Benzoin↗
PubMed1985

The effect of thiamine pyrophosphate modification on its coenzyme function in a transketolase-catalyzed reaction.

The coenzyme function of TPP analogues: 4'-NH-methyl-TPP,6'-methyl-TPP and 6'-methyl-4-nor-TPP has been studied in a transketolase-catalyzed reaction. Their dissociation constants have been found with the aid of the circular dichroism method, and coenzyme activity has been determined in a complete transketolase reaction, involving the substrate-donor and the substrate-acceptor, and also at the intermediate stage (by the alpha-carbanionic intermediate oxidation rate). The coenzyme activity values have been found different and largely dependend on the nature of the substrates used. A possibility of TPP functioning by the "two-center mechanism" in a transketolase-catalyzed reaction is discussed.

Kinetics↗
PubMed1975

Morphological study of rat thymus after tumoral, non-tumoral antigens and thiamine pyrophosphate administration.

The study was performed on 60 Wistar white rats sacrificed 24 hours and 7 days after administration of glycoprotein 8 (extracted from Jensen rat tumors), glycoprotein 5 (from normal rat blood), bovine albumin, tuberculin (PPD), and a complex of strychnine, picrotoxin and TPP administered alone or together with the above-mentioned antigens. In order to study thymus morphological changes, methods of quantitative morphology and current histological techniques were used. The thymus responds morphologically to the antigenic administration - (glycoprotein 8, bovine albumin and PPD) - by cortico-medullary ratio modification, expressed by decrease of cortical surface and increase of medullary one, thymocytes agglomeration in the perivascular sheaths and their deliverance in the blood flow. Under other conditions (strychnine, picrotoxin and TPP administration) thymus responds only by thymocytes agglomeration in the perivascular sheaths. Glycoprotein 5 does not induce any modifications in thymus structure.

Animals↗
PubMedDate not supplied

[Effect of C-4'-modification of thiamine pyrophosphate on its coenzyme activity in the oxidative decarboxylation of pyruvic acid reaction].

Interaction was studied between pyruvate dehydrogenase (EC 1.2.4.1) and C-4'-substituted analogs of thiaminpyrophosphate, 4'-N (CH3)-TPP, 4'-N(CH3)2-TPP and OH-TPP. None of these analogs was found to replace TPP during the reduction of NAD and 2.6-dichlorophenol-indophenol as well as pyruvate decarboxylation. The decarboxylase activity of the pyruvate dehydrogenase component isolated from the pyruvate dehydrogenase complex was determined according to the 14CO2 yield and production of 2-C-oxoethyl-TPP using 1-14C-pyruvate and 2-14C-pyruvate, as substrates, respectively. All the analogs were found to competitively inhibit pyruvate dehydrogenase, Ki values for 4'-N(CH3)-TPP, 4'-N(CH3)2-TPP and 4'-OH-TPP being 4.1 X 10(-5) M, 8.5 X 10(-5) M and 2.9 X 10(-6) M, respectively; Km values for TPP was equal to 1-2 X 10(-7) M. It is assumed that the analogs of the holoenzymic complex formed by the pyruvate dehydrogenase component of the pyruvate dehydrogenase complex with mono-, dimethyl-TPP and oxo-TPP do not bind the substrate.

Animals↗
PubMed1980

Erythrocyte transketolase activity in suspected cases of Leigh's disease, or subacute necrotising encephalomyelopathy.

Erythrocyte transketolase activity and the effect of adding thiamine pyrophosphate (% thiamine pyrophosphate effect) were measured in 111 subjects suspected to suffer from Leigh's disease (subacute necrotising encephalomyelopathy). From clinical evidence these subjects were divided into five groups: (1) necropsy-proved cases of subacute necrotising encephalomyelopathy, (2) cases positive for urinary thiamine pyrophosphate: adenosine triphosphate phosphotransferase inhibitor, (3) clinically likely cases of subacute necrotising encephalomyelopathy (patients still alive, or on whom no necropsy was performed), (4) cases diagnosed as diseases other than subacute necrotising encephalomyelopathy (control group), (5) cases for which no diagnosis had been made. Comparison of erythrocyte transketolase activities with and without added thiamine pyrophosphate and of the % thiamine pyrophosphate effect for each group compared with the control group showed no statistically significant differences from normal values for any of these parameters. Similarly, there were no differences between the two sexes in transketolase activity, and no correlation between transketolase activity and age. These results indicate that erythrocyte transketolase activity is not altered in subacute necrotising encephalomyelopathy and is unlikely to be of value for the diagnosis of Leigh's disease.

Brain Stem↗
PubMed1998

Thiamine pyrophosphate-dependent and thiamine metabolizing enzymes in the deafferented cerebellum and in the intact cerebral cortex of rat.

The effects of chemical (CD) and surgical (SD) deafferentation of the cerebellum on thiamine pyrophosphate (ThPP)- dependent enzymes (transketolase, TK; pyruvate-, PDH, and alpha-ketoglutarate, alphaKGDH, dehydrogenases) and thiamine (Th) metabolizing enzymes (thiamine pyrophosphokinase, ThPK; thiamine mono-, ThMPase, and pyrophosphatases, ThPPase) were evaluated in vitro in rats in steady state conditions. The enzymes were also determined in the intact cerebral cortex of the same animals. CD was carried out by i.p. injection of 3-acetylpyridine, followed by harmaline and niacinamide. SD was carried out by complete dissection of the peduncles of the left cerebellar hemisphere. Chemical and surgical cerebellar deafferentations significantly lowered the contents of both Th-metabolizing and ThPP-dependent enzymes in the cerebellum without modifying those of the cerebral cortex. ThPK and TK, which are particularly concentrated in neurons, were the most affected enzymes. The decrease in ThPP-dependent enzymes shown here is associated with the slowing down of the Th phosphorylation-dephosphorylation cycle and with no modification in the ThPP content in the cerebellum, both of which were found in a previous study. Cerebellar deafferentation seems to only affect the apoenzyme moiety of the enzymes.

Afferent Pathways↗
PubMed1991

Determination of thiamine and its phosphate esters by gradient-elution high-performance liquid chromatography.

A high-performance liquid chromatographic method for the determination of thiamine and its phosphate esters using gradient elution is presented. Chromatography was performed on an octadecyl C18 column with post-column derivatization using potassium ferricyanide: thiamine was oxidized to thiochrome, which was detected fluorimetrically. The gradient system avoids the use of a modifier and an ion-pairing reagent. The proposed method enables the separation of thiamine triphosphate, thiamine pyrophosphate, thiamine monophosphate and free thiamine, at concentrations of ca. 2 nM, within 10 min The within-assay precision for blood and serum total thiamine was less than 2 and 5%, respectively, and the between-day variation was less than 3 and 5%, respectively. The method is simple and rapid, and it can be used for screening of thiamine deficiency and for clinical study of various diseases related to vitamin B1 deficiency.

Chromatography, High Pressure Liquid↗
PubMed1968

Oxidative decarboxylation of retinoic acid in microsomes of rat liver and kidney.

Liver and kidney microsomes have been found to catalyze a rapid decarboxylation of retinoic acid in vitro. The reaction requires NADPH and Fe(2+), and is further stimulated by the presence of pyrophosphate. Thiamine pyrophosphate contained sufficient iron as an impurity to provide strong enhancement of the reaction in the absence of added iron. The decarboxylation could also be shown to occur nonenzymatically in the presence of ascorbate, Fe(2+), and boiled microsomes, but there was little autoxidation resulting in decarboxylation. The reaction was strongly inhibited by chelating agents, N,N'-diphenyl-p-phenylene diamine, phenazine methosulfate, and ferricyanide, and resembled lipid peroxidation in both its cofactor requirements and response to inhibitors. The product of the reaction appeared to lack only the C-15 of the original retinoic acid molecule. It was not retained by diethylaminoethyl cellulose, was more polar than retinoic acid upon silicic acid chromatography, had a lower UV absorption maximum (295 m micro ) than the starting product, and seemed to have an aldehyde group at C-14. The physiological significance of the decarboxylation remains to be assessed, but its rapidity makes it important to in vitro work on retinoic acid.

Acids↗
PubMed1981

Thiamin status of a Melanesian population.

A semiautomated method is described which uses the Abbott ABA-100 bichromatic analyzer to measure the stimulation of erythrocyte transketolase by thiamin pyrophosphate (the thiamin pyrophosphate effect). The method was accurate with a throughput of 30 samples per hour and is suitable for the study of the thiamin status of large populations. A significant proportion (21%) of a total of 1920 individuals of a predominantly Melanesian population were found to have an elevated thiamin pyrophosphate effect (greater than 15% activation). This same proportion with an elevated thiamin pyrophosphate effect was found in an urban hospital patient group of 346 individuals. Statistical analysis indicated a significant inverse correlation between thiamin pyrophosphate effect and plasma potassium concentration (p less than 0.001). Analysis of human fecal samples for thiaminase I activity demonstrated that this enzyme was present in 23 of a total of 46 samples selected from both the Melanesian and urban hospital patient groups. Preliminary findings indicated that the thiaminase originated from a bacterial source.

Adolescent↗
PubMed1994

Further studies on erythrocyte thiamin transport and phosphorylation in seven patients with thiamin-responsive megaloblastic anaemia.

Erythrocyte thiamin metabolism and transport were investigated in 7 patients from Brazil, Israel and Italy suffering from thiamin-responsive megaloblastic anaemia (TRMA) associated with diabetes mellitus and sensorineural deafness. All patients discontinued thiamin therapy for 4-7 days before the investigation. TRMA patients showed invariably reduced total thiamin levels in erythrocytes (percentage reduction compared with healthy controls, -46.8 +/- 3%; mean +/- SEM). The proportions of individual thiamin compounds, expressed as a percentage of total thiamin content, were within the normal range, whereas their absolute amounts were significantly decreased in the following order: thiamin monophosphate > thiamin pyrophosphate > thiamin. Thiamin pyrophosphokinase activity was also reduced as compared with controls (mean reduction +/- SEM, -25.9 +/- 1%). The saturable, specific component of thiamin uptake, which normally prevails at physiological concentrations of thiamin (< 2 mumol/L), was absent in erythrocytes obtained from TRMA patients, while the non-saturable (diffusive) component of uptake was normally present. These results confirm observations made previously in two patients and demonstrate that TRMA is consistently associated with a state of thiamin deficiency, which is presumably secondary to reduced thiamin cellular transport and absorption (caused by lack of a membrane-specific carrier), and to impaired intracellular pyrophosphorylation.

Anemia, Megaloblastic↗