Pyruvic oxidase function

Oxidative decarboxylations of a-keto acids are mediated by either enzymes having more than one cofactor or complex multienzyme systems utilizing a number of cofactors. For example, pyruvate oxidase uses TPP and FAD as coenzymes, the function of the latter being to oxidize the intermediate (41). Conversion of pyruvate to acetyl-CoA requires a multienzyme complex with the involvement of no less than five coenzymes, TPP, CoA, dihydrolipoate, FAD and NAD+ (74ACR40). 

The antidotal properties of BAL arc a.ssociatcd with the property of heavy metals to react with sullliydryl (SH) groups in proteins (e.g., tlie en/.yme pyruvate oxidase) and interfere with their normal function. 1.2-Dilhiol compounds such as BAL compete effectively with such proteins for the metal by reversibly forming metal ring compounds of the following type ... 

A mechamsm that involves protonation of the a-carbanion/enamine of HEThDP and subsequent hydride transfer, which has been proposed for several flavine-dependent enzymes (Pollegioni et al., 1997), is unlikely since no kinetic solvent isotope effect is evident for this catalytic step (Pig. 16.7). In accordance, after replacement of PAD by 5-carba-5-deaza-FAD, a PAD analog not catalyzing a transfer of single electrons but functioning as hydride acceptor, no reduction is observed by the HEThDP intermediate in pyruvate oxidase from Lactobacillus plantarum (Tittmann et al., 1998). 

The reaction catalyzed by the clostridial pyruvate oxidase is a reversible reaction. In the presence of reduced ferredoxin, CO2 may be fixed to form pyruvate, which then can be used in various metabolic reactions and is believed to be a very important reaction in certain of the photosynthetic bacteria where the reaction was first discovered (46), In the Clostridia, however, the enzyme appears to function in the direction of pyruvate oxidation (47). 

Water-soluble cydophanes are also studied as possible catalysts or artificial enzymes the hydrophobic cav-itiy serves as substrate binding site while appended functional groups act as cofactors. The pyruvate oxidase mimic 20 performed remarkably in the oxidation of aromatic aldehydes to the cossesponding esters (MeOH/ H2O), and it displayed Michaelis-Menten kinetics comparable to those of natural enzymes. The encapsulation of cydophanes in dendrimers creates binding sites within microenvironments, resembling those existing in protein superstructures. 

Mattel, P. Diederich, F. A flavo-thiazolio-cyclophane as a functional model for pyruvate oxidase. Angew. Chem., Int. Ed. Engl. 1996, 35 (12), 1341-1344. 

An anaerobic organism, Clostridium butyricum, contains a pyruvic oxidase that requires CoA and Fe++ in addition to cocarboxylase. The function of the Fe++ is not clear it may be in the electron transport. Crude extracts of this organism carry out a dismutation of pyruvate ... 

We have in the present chapter shown results from theoretical model system studies of the catalytic reaction mechanisms of three radical enzymes Galatose oxidase. Pyruvate formate-lyase and Ribonucleotide reductase. It is concluded that small models of the key parts of the active sites in combination with the DPT hybrid functional B3LYP and large basis sets provides a good description of the catalytic machineries, with low barriers for the rate determining steps and moderate overall exothermicity. The models employed are furthermore able to reproduce all the observed features in terms of spin distributions and reactive intermediates. 

Maturation effected the following changes In enzymes and metabolites in orange fruit ethanol and acetaldehyde accumulated to levels of 10 mM and 0.08 mM, pyruvate decreased about 30%, pyruvate decarboxylase increased over 4 fold, alcohol dehydrogenase increased about 2 fold, the NADH to NAD ratio increased 21/2 fold and the terminal oxidase developed CN-insensitivity. The fraction of the total alternative respiratory pathway in actual use increased from 0.46 to 1.08. Induction of the alternative, CN-insensitive oxidase during maturation was interpreted as indicating that membrane function was modified which affected metabolic pathways resulting in the accumulation of ethanol and acetaldehyde. 

Ethanol accumulated in maturing citrus fruit as the end product of pyruvate decarboxylation. Conditions that promote this reaction include low and high CC, and ethylene levels. Maturation increased the levels of PDC and ADH and increased the NADH to NAD ratio. The higher redox ratio could slow the PDH reaction which competes with PDC for pyruvate. Development of the alternative oxidase activity when ethanol began to accumulate suggests that membrane function was modified which affected rates of various metabolic pathways. The lower phosphorylation efficiency of the alternative oxidase compared to the cytochrome pathway (22) could affect numerous metabolic activities including decarboxylation of pyruvate. Also, membrane transport of pyruvate and cofactors could be altered in mitochondria containing fewer phosphorylation sites (26). 

Castignetti D, Petithory JR, Hollocher TC (1983) Pathway of oxidation of pyruvic oxime by a heterotrophic nitrifier of the genus Alcaligenes evidence against hydrolysis to pyruvate and hydroxylamine. Arch Biochem Biophys 224 587-593 Caughey WS (1971) Structure-function relationships in cytochrome c oxidase and other hemo-proteins. Adv Chem Ser 100 248-269... 

Their acute toxicity to mammals is low, but the two active substances may cause dermatitis. In rats fed daily on a diet containing quinomethionate a high cumulative toxicity was observed. A dietary level of 500 mg/kg for 90 days reduced body-weight, caused hypertrophy of the liver, and inhibited acetoacetate synthesis and the microsomal enzymes. It primarily inhibited the function of the HS-enzymes (pyruvate dehydrogenase, succinate dehydrogenase, malate dehydrogenase and a-ketoglutarate oxidase) (Carlson and DuBois, 1970). 

Study of the mechanism of the oxidation of pyruvic acid by certain bacteria led to the discovery of lipoic acid (thioctic acid) as a nutrient metabolite essential for the oxidative decarboxylation of a-keto acids. It subsequently was determined that the acetate-replacing factor " for lactic acid bacteria and protogen,a growth factor for the protozoan, Tetrahymena gelii, were also identical with lipoic acid. The occurrence of considerable quantities of lipoic acid in mammalian preparations of pyruvate and a-ketoglutarate oxidases suggests that it has the same function in animal tissues as in microorganisms. ... 

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