The mechanism of action of aldolases

Aldolases Utilize Different Oligomeric States To Preserve Their Functional Dynamics

Aldolases are essential enzymes in the glycolysis pathway and catalyze the reaction cleaving fructose/tagatose 1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. To determine how the aldolase motions relate to its catalytic process, we studied the dynamics of three different class II aldolase structures through simulations. We employed coarse-grained elastic network normal-mode analyses to investigate the dynamics of Escherichia coli fructose 1,6-bisphosphate aldolase, E. coli tagatose 1,6-bisphosphate aldolase, and Thermus aquaticus fructose 1,6-bisphosphate aldolase and compared their motions in different oligomeric states. The first one is a dimer, and the second and third are tetramers. Our analyses suggest that oligomerization not only stabilizes the aldolase structures, showing fewer fluctuations at the subunit interfaces, but also allows the enzyme to achieve the required dynamics for its functional loops. The essential mobility of these loops in the functional oligomeric states can facilitate the enzymatic mechanism, substrate recruitment in the open state, bringing the catalytic residues into their required configuration in the closed bound state, and moving back to the open state to release the catalytic products and repositioning the enzyme for its next catalytic cycle. These findings suggest that the aldolase global motions are conserved among aldolases having different oligomeric states to preserve its catalytic mechanism. The coarse-grained approaches taken permit an unprecedented view of the changes in the structural dynamics and how these relate to the critical structural stabilities essential for catalysis. The results are supported by experimental findings from many previous studies.

Analysis of Chinese hamster ovary cell metabolism through a combined computational and experimental approach

Optimization of cell culture processes can benefit from the systematic analysis of experimental data and their organization in mathematical models, which can be used to decipher the effect of individual process variables on multiple outputs of interest. Towards this goal, a kinetic model of cytosolic glucose metabolism coupled with a population-level model of Chinese hamster ovary cells was used to analyse metabolic behavior under batch and fed-batch cell culture conditions. The model was parameterized using experimental data for cell growth dynamics, extracellular and intracellular metabolite profiles. The results highlight significant differences between the two culture conditions in terms of metabolic efficiency and motivate the exploration of lactate as a secondary carbon source. Finally, the application of global sensitivity analysis to the model parameters highlights the need for additional experimental information on cell cycle distribution to complement metabolomic analyses with a view to parameterize kinetic models.

Crystal structure analysis of L-fuculose-1-phosphate aldolase from Thermus thermophilus HB8 and its catalytic action: as explained through in silico

Fuculose phosphate aldolase catalyzes the reversible cleavage of fuculose-1-phosphate to dihydroxyacetone phosphate and L-lactaldehyde. A tetramer by nature, this enzyme from Thermus thermophilus HB8 represents the group of Class II aldolases. The structure was solved in two different space groups using the crystals obtained from slow evaporation vapour-diffusion and microbatch techniques. The detailed crystallization description has been reported previously. In this study, the structural features of fuculose phosphate aldolase from T. thermophilus have been explored extensively through sequence and structure comparisons with fuculose phosphate aldolases of different species. Finally, an in silico analysis using induced fit docking was attempted to deduce the binding mode of fuculose phosphate aldolase with its natural substrate fuculose-1-phosphate along with a substrate analog dihydroxyacetone phosphate and phosphoglycolohydroxymate--a potential aldolase inhibitor. The results show the mechanism of action may be similar to that of Escherichia coli fuculose aldolase.

The placenta: transcriptional, epigenetic, and physiological integration during development

The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface relies on coordinated interactions among transcriptional, epigenetic, and environmental factors. Here we describe these mechanisms in the context of the differentiation of placental cells (trophoblasts) and synthesize current knowledge about how they interact to generate a functional placenta. Developing an understanding of these pathways contributes to an improvement of our models for studying trophoblast biology and sheds light on the etiology of pregnancy complications and the in utero programming of adult diseases.

Effects of water restriction on gene expression in mouse renal medulla: identification of 3βHSD4 as a collecting duct protein

To identify novel gene targets of vasopressin regulation in the renal medulla, we performed a cDNA microarray study on the inner medullary tissue of mice following a 48-h water restriction protocol. In this study, 4,625 genes of the possible ∼12,000 genes on the array were included in the analysis, and of these 157 transcripts were increased and 63 transcripts were decreased by 1.5-fold or more. Quantitative, real-time PCR measurements confirmed the increases seen for 12 selected transcripts, and the decreases were confirmed for 7 transcripts. In addition, we measured transcript abundance for many renal collecting duct proteins that were not represented on the array; aquaporin-2 (AQP2), AQP3, Pax-8, and α- and β-Na-K-ATPase subunits were all significantly increased in abundance; the β- and γ-subunits of ENaC and the vasopressin type 1A receptor were significantly decreased. To correlate changes in mRNA expression with changes in protein expression, we carried out quantitative immunoblotting. For most of the genes examined, changes in mRNA abundances were not associated with concomitant protein abundance changes; however, AQP2 transcript abundance and protein abundance did correlate. Surprisingly, aldolase B transcript abundance was increased but protein abundance was decreased following 48 h of water restriction. Several transcripts identified by microarray were novel with respect to their expression in mouse renal medullary tissues. The steroid hormone enzyme 3β-hydroxysteroid dehydrogenase 4 (3βHSD4) was identified as a novel target of vasopressin regulation, and via dual labeling immunofluorescence we colocalized the expression of this protein to AQP2-expressing collecting ducts of the kidney. These studies have identified several transcripts whose abundances are regulated in mouse inner medulla in response to an increase in endogenous vasopressin levels and could play roles in the regulation of salt and water excretion.

Purification, crystallization and preliminary X-ray crystallographic study of the L-fuculose-1-phosphate aldolase (FucA) from Thermus thermophilus HB8

Fuculose phosphate aldolase catalyzes the reversible cleavage of L-fuculose-1-phosphate to dihydroxyacetone phosphate and L-lactaldehyde. The protein from Thermus thermophilus HB8 is a biological tetramer with a subunit molecular weight of 21 591 Da. Purified FucA has been crystallized using sitting-drop vapour-diffusion and microbatch techniques at 293 K. The crystals belong to space group P4, with unit-cell parameters a = b = 100.94, c = 45.87 A. The presence of a dimer of the enzyme in the asymmetric unit was estimated to give a Matthews coefficient (VM) of 2.7 A3 Da(-1) and a solvent content of 54.2%(v/v). Three-wavelength diffraction MAD data were collected to 2.3 A from zinc-containing crystals. Native diffraction data to 1.9 A resolution have been collected using synchrotron radiation at SPring-8.

Structure of the polyketide cyclase SnoaL reveals a novel mechanism for enzymatic aldol condensation

SnoaL belongs to a family of small polyketide cyclases, which catalyse ring closure steps in the biosynthesis of polyketide antibiotics produced in Streptomyces. Several of these antibiotics are among the most used anti-cancer drugs currently in use. The crystal structure of SnoaL, involved in nogalamycin biosynthesis, with a bound product, has been determined to 1.35 A resolution. The fold of the subunit can be described as a distorted alpha+beta barrel, and the ligand is bound in the hydrophobic interior of the barrel. The 3D structure and site-directed mutagenesis experiments reveal that the mechanism of the intramolecular aldol condensation catalysed by SnoaL is different from that of the classical aldolases, which employ covalent Schiff base formation or a metal ion cofactor. The invariant residue Asp121 acts as an acid/base catalyst during the reaction. Stabilisation of the enol(ate) intermediate is mainly achieved by the delocalisation of the electron pair over the extended pi system of the substrate. These polyketide cyclases thus form of family of enzymes with a unique catalytic strategy for aldol condensation.

Crystal structures of the metal-dependent 2-dehydro-3-deoxy-galactarate aldolase suggest a novel reaction mechanism

Carbon-carbon bond formation is an essential reaction in organic chemistry and the use of aldolase enzymes for the stereochemical control of such reactions is an attractive alternative to conventional chemical methods. Here we describe the crystal structures of a novel class II enzyme, 2-dehydro-3-deoxy-galactarate (DDG) aldolase from Escherichia coli, in the presence and absence of substrate. The crystal structure was determined by locating only four Se sites to obtain phases for 506 protein residues. The protomer displays a modified (alpha/beta)(8) barrel fold, in which the eighth alpha-helix points away from the beta-barrel instead of packing against it. Analysis of the DDG aldolase crystal structures suggests a novel aldolase mechanism in which a phosphate anion accepts the proton from the methyl group of pyruvate.

Crystal structure of human muscle aldolase complexed with fructose 1,6-bisphosphate: mechanistic implications

Fructose 1,6-bisphosphate aldolase catalyzes the reversible cleavage of fructose 1,6-bisphosphate and fructose 1-phosphate to dihydroxyacetone phosphate and either glyceraldehyde 3-phosphate or glyceraldehyde, respectively. Catalysis involves the formation of a Schiff's base intermediate formed at the epsilon-amino group of Lys229. The existing apo-enzyme structure was refined using the crystallographic free-R-factor and maximum likelihood methods that have been shown to give improved structural results that are less subject to model bias. Crystals were also soaked with the natural substrate (fructose 1,6-bisphosphate), and the crystal structure of this complex has been determined to 2.8 A. The apo structure differs from the previous Brookhaven-deposited structure (1ald) in the flexible C-terminal region. This is also the region where the native and complex structures exhibit differences. The conformational changes between native and complex structure are not large, but the observed complex does not involve the full formation of the Schiff's base intermediate, and suggests a preliminary hydrogen-bonded Michaelis complex before the formation of the covalent complex.

Metabolic Control Analysis of glycolysis in tuber tissue of potato (Solanum tuberosum): explanation for the low control coefficient of phosphofructokinase over respiratory flux

We have applied Metabolic Control Analysis (MCA) in an attempt to determine the distribution of glycolytic flux control between the steps of glycolysis in aged disks of potato tuber under aerobic conditions, using concentrations of glycolytic metabolites in tuber tissue from a range of transgenic potato plants and published enzyme kinetic data. We modelled the substrate and effector kinetics of potato tuber phosphofructokinase (PFK) by reanalysing published results. Despite the scarcity of reliable kinetic data, our results are in agreement with experimental findings namely that, under the conditions described, PFK has little control over glycolytic flux. Furthermore our analysis predicts that under these conditions far more control lies in the dephosphorylation of phosphoenolpyruvate and/or in the steps beyond. We have validated the results of our analysis in two ways. First, predictions based on calculated concentration control coefficients from the analysis show generally good agreement with observed metabolite deviation indices discussed in the preceding paper [Thomas, Mooney, Burrell, and Fell (1997) Biochem. J. 322, 111-117]. Second, sensitivity analysis of our results shows that the calculated control coefficients are robust to errors in the elasticities used in the analysis, of which relatively few need to be known accurately. Experimental and control analysis results agree with previous predictions of MCA that strong co-operative feedback inhibition of enzymes serves to move flux control downstream of the inhibiting metabolite. We conclude that MCA can successfully model the outcome of experiments in the genetic manipulation of enzyme amounts.

Cloning, sequence analysis and over-expression of the gene for the class II fructose 1,6-bisphosphate aldolase of Escherichia coli

Nucleotide sequence analysis of the Escherichia coli chromosomal DNA inserted in the plasmid pLC33-5 of the Clarke and Carbon library [Clarke & Carbon (1976) Cell 9, 91-99] revealed the existence of the gene, fda, encoding the Class II (metal-dependent) fructose 1,6-bisphosphate aldolase of E. coli. The primary structure of the polypeptide chain inferred from the DNA sequence of the fda gene comprises 359 amino acids, including the initiating methionine residue, from which an Mr of 39,146 could be calculated. This value is in good agreement with that of 40,000 estimated from sodium dodecyl sulphate-polyacrylamide gel electrophoresis of the purified dimeric enzyme. The amino acid sequence of the Class II aldolase from E. coli showed no homology with the known amino acid sequences of Class I (imine-forming) fructose 1,6-bisphosphate aldolases from a wide variety of sources. On the other hand, there was obvious homology with the N-terminal sequence of 40 residues already established for the Class II fructose 1,6-bisphosphate aldolase of Saccharomyces cerevisiae. These Class II aldolases, one from a prokaryote and one from a eukaryote, evidently are structurally and evolutionarily related. A 1029 bp-fragment of DNA incorporating the fda gene was excised from plasmid pLC33-5 by digestion with restriction endonuclease HaeIII and subcloned into the expression plasmid pKK223-3, where the gene came under the control of the tac promoter. When grown in the presence of the inducer isopropyl-beta-D-thiogalactopyranoside, E. coli JM101 cells transformed with this recombinant expression plasmid generated the Class II fructose 1,6-bisphosphate aldolase as approx. 70% of their soluble protein. This unusually high expression of an E. coli gene should greatly facilitate purification of the enzyme for any future structural or mechanistic studies.

The chemical mechanism of sheep liver 6-phosphogluconate dehydrogenase. A Schiff-base intermediate is not involved

[2-18O]Ribulose 5-phosphate was prepared and shown to be converted enzymically by 6-phosphogluconate dehydrogenase from sheep liver into 6-phosphogluconate with complete retention of the heavy isotope. This finding unequivocally excludes the possibility of a Schiff-base mechanism for the enzyme. The involvement of metal ions has already been excluded, and other possible mechanisms are discussed. The enzyme was purified by an improved large-scale procedure, which is briefly described.

Metal-replacement studies in Bacillus stearothermophilus aldolase and a comparison of the mechanisms of class I and class II aldolases

A comparison of the product-inhibition patterns during cleavage of D-fructose 1,6-diphosphate by aldolases from yeast, rabbit muscle and Bacillus stearothermophilus shows an ordered reaction sequence for all three enzymes, with dihydroxyacetone phosphate the last-leaving product. Addition of Zn2+, Co2+, Fe2+, Mn2+ or Cd2+ ions to the inactive apo-(Bacillus stearothermophilus aldolase) restores activity to different extents, whereas Ni2+, Mg2+ or Cu2+ ions have no effect. The cleavage activity of this aldolase is not enhanced by added K+ ion. The effects of metal replacement on thermal stability, Km and Vmax. are given and the possible role of the metal is discussed in the light of these results.

Studies on the subunit structure of 4-deoxy-5-oxoglucarate hydro-lyase (decarboxylating) from Pseudomonas acidovorans

1. Homogeneous preparations of D-4-deoxy-5-oxoglutarate hydro lyase (decarboxylating)(EC4.2.1.41) were analysed in the ultracentrifuge by the high-speed sedimentation-equilibrium method of Yphantis (1964). The molecular weight in 0.1 M-potassium phosphate buffer, pH 7.2, in 6M-guanidine hydrochloride and in 0.1 M-beta-mercaptoethanol in 6M-guanidine hydrochloride was 113,000, 56,000 and 30,400 respectively. Polyacrylamidegel electrophoresis in the presence of sodium dodecyl sulphate indicated a minimum molecular weight of 30,500. 2. Measurement of the thiol content of the enzyme, before and after reduction with NaBH4 or dithiothreitol under denaturing conditions, indicated the presence of eight thiol residues and two interchain disulphide bridges/enzyme molecule. 3. Amino acid analysis showed that the intact enzyme contains a total of approximately 100 arginine and lysine residues, but digestion of the enzyme with trypsin yielded about 49 peptides staining with ninhydrin in a peptide "map". 4. With the knowledge that the enzyme contains only two substrate-binding sites, it is suggested that the enzyme probably consists of four polypeptide chains arranged in an alpha2beta2 confirmation.

Studies on glucarate catabolism: the oxodeoxyglucarate aldolase activity of glucarate hydro-lyase from Pseudomonas acidovorans

Glucarate hydro-lyase was isolated and purified to near homogeneity from cells of Pseudomonas acidovorans grown on glucarate. By using gel filtration and ion-exchange chromatography, it was shown that the oxodeoxyglucarate aldolase activity observed in such extracts is associated with the glucarate hydro-lyase protein.

Purification and characterization of two fructose diphosphate aldolases from Escherichia coli (Crookes' strain)

Two fructose diphosphate aldolases (EC 4.1.2.13) were detected in extracts of Escherichia coli (Crookes' strain) grown on pyruvate or lactate. The two enzymes can be resolved by chromatography on DEAE-cellulose at pH7.5, or by gel filtration on Sephadex G-200, and both have been obtained in a pure state. One is a typical bacterial aldolase (class II) in that it is strongly inhibited by metal-chelating agents and is reactivated by bivalent metal ions, e.g. Ca(2+), Zn(2+). It is a dimer with a molecular weight of approx. 70000, and the K(m) value for fructose diphosphate is about 0.85mm. The other aldolase is not dependent on metal ions for its activity, but is inhibited by reduction with NaBH(4) in the presence of substrate. The K(m) value for fructose diphosphate is about 20mum (although the Lineweaver-Burk plot is not linear) and the enzyme is probably a tetramer with molecular weight approx. 140000. It has been crystallized. On the basis of these properties it is tentatively assigned to class I. The appearance of a class I aldolase in bacteria was unexpected, and its synthesis in E. coli is apparently favoured by conditions of gluconeogenesis. Only aldolase of class II was found in E. coli that had been grown on glucose. The significance of these results for the evolution of fructose diphosphate aldolases is briefly discussed.

Deamidation in vivo of an asparagine residue of rabbit muscle aldolase

Microheterogeneity of rabbit muscle aldolase is caused by deamidation in vivo of an asparagine residue near the C-terminus of each subunit. Isotopic labeling of a peptide containing the asparagine residue at various time intervals before isolation of aldolase permits estimation of the half-time for the deamidation as about 8 days, which is about the time estimated for the half-life of the enzyme in vivo. It is concluded that the aldolase as genetically determined is a tetramer, designated alpha(4), that undergoes random deamidation to form alpha(3)beta, alpha(2)beta(2), and alphabeta(3) species as intermediates in the formation of beta(4), the species in which all of the specific asparagine has been deamidated. Isoelectric focusing data indicate that the subunits do not exchange appreciably in vivo.

Studies on N-acetylneuraminic acid aldolase

N-Acetylneuraminic acid aldolase from Clostridium perfringens was irreversibly inactivated by 1mm-bromopyruvate with a half-life of 4.2min at pH7.2 and 37 degrees C. The rate of inactivation was diminished in the presence of pyruvate but not with N-acetyl-d-mannosamine, indicating that the inhibitor acted at, or close to, the pyruvate-binding site. The apparent K(i) for bromopyruvate, calculated from the variation of half-life with inhibitor concentration, was 0.46mm, compared with a competitive K(i) 3.0mm for pyruvate. Incubation of the enzyme with radioactive bromopyruvate gave a radioactive, enzymically inactive, protein in which the bromopyruvate had alkylated cysteine residues. Incubation of the enzyme with radioactive pyruvate, followed by reduction with sodium borohydride, led to inactivation of the enzyme and binding of the pyruvate to the protein by reduction of a Schiff's base initially formed with the in-amino group of a lysine residue; only one-twentieth as many pyruvyl residues were bound by this method, showing that bromopyruvate is not specific for the active site. After protection of the enzyme active site with pyruvate, treatment with unlabelled bromopyruvate and dialysis, the enzyme retained 72% activity. When this treated enzyme was separately incubated with radioactive bromopyruvate, or radioactive pyruvate followed by sodium borohydride, the ratio of radioactive pyruvyl residues bound by the two methods was 2.3:1. After reduction and hydrolysis of the bromopyruvate-treated enzyme, the only detectable radioactive amino acid derivative was chromatographically and electrophoretically identical with S-(3-lactic acid)-cysteine. The enzyme was fully active in the presence of EDTA and was not stimulated by bivalent metal ions. It was strongly inhibited by silver and mercuric ions. The apparent molecular weight, determined by Sephadex chromatography, was 250000. A mechanism of action is proposed for the enzyme. Bromopyruvate reacts rapidly at pH6.0 with thiol-containing amino acids. Cysteine appears to react anomalously.

Dihydroxyacetone phosphate. Its structure and reactivity with -glycerophosphate dehydrogenase, aldolase and triose phosphate isomerase and some possible metabolic implications

1. Dihydroxyacetone phosphate exists in neutral aqueous solution at 20 degrees C as a mixture of keto, gem-diol and enolic forms in the ratio 55:44:1. 2. The three forms are freely interconvertible and rate constants for these reactions have been determined. 3. Keto-dihydroxyacetone phosphate is the primary reactive species in the reactions catalysed by alpha-glycerophosphate dehydrogenase, aldolase and triose phosphate isomerase. 4. The proportion of keto form to gem-diol forms of dihydroxyacetone phosphate is temperature-dependent. At 37 degrees C, 83% is keto-dihydroxyacetone phosphate. 5. The enzymological and metabolic consequences of these results are discussed.

Photoinactivation of aldolases by pyridoxal phosphate and its analogues

Pyridoxal phosphate can act as a specific photosensitizer for amino acid residues in rabbit muscle and spinach leaf aldolases, but the residues affected depend on the pH of the reaction. Below pH 8 one histidine residue per enzyme subunit is destroyed; above pH 8.5 there is little loss of histidine, and photoinactivation is associated with the destruction of specific tyrosine residues, particularly the COOH-terminal residues. Pyridoxal and 4-pyridinecarboxaldehyde are much less effective than pyridoxal phosphate at neutral pH, but are similar to pyridoxal phosphate in their photosensitizing activity at the higher pH. Compounds lacking the aldehyde group or the pyridine ring show little or no activity. A number of other enzymes, including alpha-glycerophosphate dehydrogenase, glucose-6-phosphate dehydrogenase, and yeast hexokinase, were also photoinactivated in the presence of pyridoxal phosphate; however, rabbit liver aldolase and two isomerases tested were completely resistant. The results suggest that certain enzymes, including rabbit muscle and spinach aldolases, but not rabbit liver aldolase, contain a specific site which interacts with pyridoxal phosphate, and that the conformation of this site changes in the pH range between 8.0 and 8.5

Comparison of aldolases extracted from rabbit muscle at low and high ionic strength

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The reactivity of thiol groups and the subunit structure of aldolase

1. Seven unique carboxymethylcysteine-containing peptides have been isolated from tryptic digests of rabbit muscle aldolase carboxymethylated with iodo[2-(14)C]acetic acid in 8m-urea. These peptides have been characterized by amino acid and end-group analysis and their location within the cyanogen bromide cleavage fragments of the enzyme has been determined. 2. Reaction of native aldolase with 5,5'-dithiobis-(2-nitrobenzoic acid), iodoacetamide and N-ethylmaleimide showed that a total of three cysteine residues per subunit of mol.wt. 40000 were reactive towards these reagents, and that the modification of these residues was accompanied by loss in enzymic activity. Chemical analysis of the modified enzymes demonstrated that the same three thiol groups are involved in the reaction with all these reagents but that the observed reactivity of a given thiol group varies with the reagent used. 3. One reactive thiol group per subunit could be protected when the modification of the enzyme was carried out in the presence of substrate, fructose 1,6-diphosphate, under which conditions enzymic activity was retained. This thiol group has been identified chemically and is possibly at or near the active site. Limiting the exposure of the native enzyme to iodoacetamide also served to restrict alkylation to two thiol groups and left the enzymic activity unimpaired. The thiol group left unmodified is the same as that protected by substrate during more rigorous alkylation, although it is now more reactive towards 5,5'-dithiobis-(2-nitrobenzoic acid) than in the native enzyme. 4. Conversely, prolonged incubation of the enzyme with fructose 1,6-diphosphate, which was subsequently removed by dialysis, caused an irreversible fall in enzymic activity and in thiol group reactivity measured with 5,5'-dithiobis-(2-nitrobenzoic acid). 5. It is concluded that the aldolase tetramer contains at least 28 cysteine residues. Each subunit appears to be identical with respect to number, location and reactivity of thiol groups.

The reaction of aldolase with 2-methylmaleic anhydride

1. The reaction of rabbit muscle aldolase with 2-methylmaleic anhydride is described. All the protein amino groups can be reversibly blocked. 2. As the reaction proceeds, the enzyme activity decreases until, at about 50% citraconylation of amino groups, the enzyme is completely inhibited. At this stage, little or no dissociation of the enzyme tetramer is observed and 75% of the activity is recoverable on unblocking the amino groups. 3. At 80% blocking, the enzyme is completely dissociated but little enzymic activity is recoverable after unblocking. Inability to recover activity after citraconylation and unblocking correlates with the onset of dissociation of the citraconyl-aldolase seen on ultracentrifugation. 4. The only irreversible modification of the enzyme primary structure detectable after the citraconylation and unblocking reactions is the partial loss of thiol groups. It is probable that this is responsible for the inability to reform active enzyme from the citraconylated subunit. 5. Other reversible side reactions of maleic anhydride and citraconic anhydride that may occur with proteins are discussed.

Purification and properties of D-4-deoxy-5-oxoglucarate hydro-lyase (decarboxylating)

1. An enzyme extracted from Pseudomonas acidovorans was purified and shown to catalyse the simultaneous dehydration and decarboxylation of d-4-deoxy-5-oxoglucarate. It is proposed to name the enzyme d-4-deoxy-5-oxoglucarate hydro-lyase (decarboxylating), trivial name ;deoxyoxoglucarate dehydratase'. 2. No added cofactors were required, and the enzyme was inactivated when incubated with its substrate in the presence of sodium borohydride. Under these conditions the substrate and enzyme appeared to be bound covalently. 3. The action of the enzyme is readily explained if it is assumed that d-4-deoxy-5-oxoglucarate forms a Schiff base with a lysine residue in the enzyme.