Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.2.13 (aldolase)
 3,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Although aldolase-catalyzed condensations proceed by stepwise mechanisms via the intermediacy of nucleophilic enol(ate)s or enamines, the mechanisms of those enzymes that catalyze Claisen-type condensations are unclear. The reaction pathway followed by an enzyme from this second group, malate synthase, has been studied by the double-isotope fractionation method to determine whether the reaction is stepwise or concerted. In agreement with earlier work, a deuterium kinetic isotope effect D(V/K) of 1.3 +/- 0.1 has been found when [2H3]acetyl-CoA is the substrate. The 13C isotope effect at the aldehydic carbon of glyoxylate has also been measured. For this determination, the malate product (containing the carbon of interest at C-2) was quantitatively transformed into a new sample of malate having the carbon of interest at C-4. This material was decarboxylated by malic enzyme to produce the appropriate CO2 for isotope ratio mass spectrometric analysis. The 13C isotope effect with [1H3]acetyl-CoA [that is, 13(V/K)H] is 1.0037 +/- 0.0004. By use of the known values of the intermolecular and intramolecular deuterium effects and of 13(V/K)H, the value of the 13C isotope effect when deuteriated [2H3]acetyl-CoA is the substrate [that is, 13(V/K)D] can be predicted for three possible mechanisms. If 13(V/K)H is a kinetic isotope effect and the reaction is concerted, the value of the 13C effect on deuteriation of acetyl-CoA will rise to 1.011; if 13(V/K)H is a kinetic isotope effect and the reaction is stepwise, the value of the 13C effect will fall to 1.0025; and if the 13C effect is an equilibrium isotope effect deriving from glyoxylate dehydration, the reaction is necessarily stepwise, and the value of 13(V/K)D will be 1.0037, unchanged from that of 13(V/K)H. Experimentally, the value of 13(V/K)D is 1.0037 +/- 0.0007, which requires that malate synthase follow a stepwise path. It is therefore clear that the two salient characteristics of enzymes that catalyze Claisen-like condensations, namely, the absence of enzyme-catalyzed proton exchange with solvent and the inversion of the configuration at the nucleophilic center, which had been suggestive of a concerted pathway, are not mechanistically diagnostic.
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PMID:Malate synthase: proof of a stepwise Claisen condensation using the double-isotope fractionation test. 284 78

Cells of Azotobacter vinelandii are specifically induced to encyst by beta-hydroxybutyrate (BHB). The process of differentiation, which occurs over a period of 36 h, was characterized by an ordered sequence of biochemical events. Upon initiation of encystment, nitrogen fixation and glucose-6-phosphate dehydrogenase activities decreased immediately to very low levels. This was followed by an increase in the specific activities of BHB dehydrogenase, isocitrate dehydrogenase, isocitrate lyase, and malate synthase first at 3 h and then again at 21 h. The peak activity of fructose 1,6-diphosphate aldolase occurred at 6 h, and the enzyme activity then decreased gradually. Fructose 1,6-diphosphatase had peak activities at 9 and 27 h. Deoxyribonucleic acid synthesis ceased just prior to the final cell division at 4 to 6 h, but ribonucleic acid synthesis continued until the 12th h. From labeling studies and the appearance of new enzyme activities, it appeared that protein synthesis continued throughout encystment.
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PMID:Sequential metabolic events during encystment of Azobacter vinelandii. 434 69

The enzyme pattern of Saccharomyces cerevisiae was followed during batch growth and in continuous culture in a synthetic medium limited for glucose under aerobic conditions. Seven enzymes were measured: succinate-cytochrome c oxidoreductase, malate dehydrogenase, nicotinamide adenine dinucleotide-linked glutamate dehydrogenase, malate synthase, isocitrate lyase, aldolase, and nicotinamide adenine dinucleotide phosphate (NADP(+))-linked glutamate dehydrogenase. During fermentation of glucose and high growth rate (mu) during the first log phase in batch experiments, the first five enzymes (group I) were repressed, and aldolase and NADP(+)-linked glutamate dehydrogenase (group II) were derepressed. During growth on the accumulated ethyl alcohol and lower mu, the group I enzymes were preferentially formed and the other two were repressed. A sequence of derepression of the group I enzymes was found during the shift from glucose to ethyl alcohol metabolism, which can be correlated with a strong increase in the percentage of single (nonbudding) cells in the population. A correlation between the state of cells in the budding cycle and enzyme repression and derepression is suggested. In continuous culture, the enzyme pattern was shown to be related to the growth rate. The group I enzymes were repressed at high growth rates, while the group II enzymes were derepressed. Each enzyme exhibits a different dependence. The enzyme pattern is shown to depend on the rate of substrate consumption as well as on the type of metabolism and to be correlated with the budding cycle. The enzyme pattern is considered to be controlled by changes of intracellular catabolic or metabolic conditions inherent in the division cycle.
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PMID:Enzyme pattern and aerobic growth of Saccharomyces cerevisiae under various degrees of glucose limitation. 438 90

The leucine biosynthetic pathway is essential for the growth of Mycobacterium tuberculosis and is a potential target for the design of new anti-tuberculosis drugs. The crystal structure of alpha-isopropylmalate synthase, which catalyzes the first committed step in this pathway, has been determined by multiwavelength anomalous dispersion methods and refined at 2.0-A resolution in complex with its substrate alpha-ketoisovalerate. The structure reveals a tightly associated, domain-swapped dimer in which each monomer comprises an (alpha/beta)(8) TIM barrel catalytic domain, a helical linker domain, and a regulatory domain of novel fold. Mutational and crystallographic data indicate the latter as the site for leucine feedback inhibition of activity. Domain swapping enables the linker domain of one monomer to sit over the catalytic domain of the other, inserting residues into the active site that may be important in catalysis. The alpha-ketoisovalerate substrate binds to an active site zinc ion, adjacent to a cavity that can accommodate acetyl-CoA. Sequence and structural similarities point to a catalytic mechanism similar to that of malate synthase and an evolutionary relationship with an aldolase that catalyzes the reverse reaction on a similar substrate.
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PMID:Crystal structure of LeuA from Mycobacterium tuberculosis, a key enzyme in leucine biosynthesis. 1515 44

We have previously shown that the hyperthermophilic archaeon, Sulfolobus solfataricus, catabolizes d-glucose and d-galactose to pyruvate and glyceraldehyde via a non-phosphorylative version of the Entner-Doudoroff pathway. At each step, one enzyme is active with both C6 epimers, leading to a metabolically promiscuous pathway. On further investigation, the catalytic promiscuity of the first enzyme in this pathway, glucose dehydrogenase, has been shown to extend to the C5 sugars, D-xylose and L-arabinose. In the current paper we establish that this promiscuity for C6 and C5 metabolites is also exhibited by the third enzyme in the pathway, 2-keto-3-deoxygluconate aldolase, but that the second step requires a specific C5-dehydratase, the gluconate dehydratase being active only with C6 metabolites. The products of this pathway for the catabolism of D-xylose and L-arabinose are pyruvate and glycolaldehyde, pyruvate entering the citric acid cycle after oxidative decarboxylation to acetyl-coenzyme A. We have identified and characterized the enzymes, both native and recombinant, that catalyze the conversion of glycolaldehyde to glycolate and then to glyoxylate, which can enter the citric acid cycle via the action of malate synthase. Evidence is also presented that similar enzymes for this pentose sugar pathway are present in Sulfolobus acidocaldarius, and metabolic tracer studies in this archaeon demonstrate its in vivo operation in parallel with a route involving no aldol cleavage of the 2-keto-3-deoxy-pentanoates but direct conversion to the citric acid cycle C5-metabolite, 2-oxoglutarate.
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PMID:Metabolism of pentose sugars in the hyperthermophilic archaea Sulfolobus solfataricus and Sulfolobus acidocaldarius. 2073 70

Paracoccidioides species are dimorphic fungi and are the etiologic agents of paracoccidioidomycosis, which is a serious disease that involves multiple organs. The many tissues colonized by this fungus suggest a variety of surface molecules involved in adhesion. A surprising finding is that most enzymes in the glycolytic pathway, tricarboxylic acid (TCA) cycle and glyoxylate cycle in Paracoccidioides spp. have adhesive properties that aid in interacting with the host extracellular matrix and thus act as 'moonlighting' proteins. Moonlighting proteins have multiple functions, which adds a dimension to cellular complexity and benefit cells in several ways. This phenomenon occurs in both eukaryotes and prokaryotes. For example, moonlighting proteins from the glycolytic pathway or TCA cycle can play a role in bacterial pathogenesis by either acting as proteins secreted in a conventional pathway and/or as cell surface components that facilitate adhesion or adherence. This review outlines the multifunctionality exhibited by many Paracoccidioides spp. enzymes, including aconitase, aldolase, glyceraldehyde-3-phosphate dehydrogenase, isocitrate lyase, malate synthase, triose phosphate isomerase, fumarase, and enolase. We discuss the roles that moonlighting activities play in the virulence characteristics of this fungus and several other human pathogens during their interactions with the host.
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PMID:The multifaceted roles of metabolic enzymes in the Paracoccidioides species complex. 2556 29