Poly(fumaric-co-sebacic anhydride). A degradation study as evaluated by FTIR, DSC, GPC and X-ray diffraction

The degradation of three poly(fumaric-co-sebacic anhydride) [P(FA:SA)] copolymers is examined in a composition of microspheres made by the hot melt encapsulation process. The emergence of low molecular weight oligomers occurs during degradation of the copolymer microspheres, as evidenced by a variety of characterization methods. Characterization was conducted to determine the extent of degradation of the polyanhydride microspheres using Fourier-transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and X-ray diffraction. It is demonstrated that degradation of P(FA:SA) is greatly accelerated at basic pH, yet there is little difference between degradation in neutral and acidic buffers. A good correlation exists between the results of each characterization method, which allows a better understanding of the degradation process and the resulting formation of low molecular weight oligomers in poly(fumaric-co-sebacic anhydride).

Synthesis of poly(propylene fumarate) by acylation of propylene glycol in the presence of a proton scavenger

To synthesize high molecular weight poly(propylene fumarate) (PPF), fumaryl chloride and propylene glycol were reacted in the presence of potassium carbonate, which serves as a proton scavenger. Transesterification of the resulting low molecular weight oligomer led to a polymer with greater molecular weight than those from previous reaction methods without requiring the use of a catalyst. According to two-dimensional NMR, the backbone structure of this polymer was as expected and contained no byproducts formed by acid catalyzed addition across the fumarate double bond. Kinetic studies of the transesterification showed that the molecular weight reached a final Mn of 4900 (+/-700) and Mw of 9100 (+/-1300) after 16 h, while the polydispersity index remained below 1.8 throughout the reaction. Thus the PPF synthesized by the new method is of higher molecular weight and greater purity than our previously prepared material.

Crosslinking characteristics of an injectable poly(propylene fumarate)/beta-tricalcium phosphate paste and mechanical properties of the crosslinked composite for use as a biodegradable bone cement

We investigated the crosslinking characteristics of an injectable composite paste of poly(propylene fumarate) (PPF), N-vinyl pyrrolidinone (N-VP), benzoyl peroxide (BP), sodium chloride (NaCl), and beta-tricalcium phosphate (beta-TCP). We examined the effects of PPF molecular weight, N-VP/PPF ratio, BP/PPF ratio, and NaCl weight percent on the crosslinking temperature, heat release upon crosslinking, gel point, and the composite compressive strength and modulus. The maximum crosslinking temperature did not vary widely among formulations, with the absolute values falling between 38 degrees and 48 degrees C, which was much lower than that of 94 degrees C for poly(methyl methacrylate) bone cement controls tested under the same conditions. The total heat released upon crosslinking was decreased by an increase in PPF molecular weight and a decrease in N-VP/PPF ratio. The gel point was affected strongly by the PPF molecular weight, with a decrease in PPF molecular weight more rapidly leading to a gel point. An increase in initiator concentration had the same effect to a lesser degree. The time frame for curing was varied from 1-121 min, allowing the composite to be tailored to specific applications. The compressive strength and compressive modulus values increased with decreasing N-VP/PPF, increasing NaCl content, and increasing BP/PPF ratio. For all formulations, the compressive strength values fell between 1 and 12 MPa, and the compressive modulus values fell between 23 and 265 MPa. These data suggest that injectable PPF/beta-TCP pastes can be prepared with handling characteristics appropriate for clinical orthopedic applications and that the mechanical properties of the cured composites are suitable for trabecular bone replacement.

Designed four-helix bundle catalysts--the engineering of reactive sites for hydrolysis and transesterification reactions of p-nitrophenyl esters

Four-helix bundle proteins have been designed that catalyze the hydrolysis and transesterification reactions of p-nitrophenyl esters by a cooperative nucleophilic and general acid mechanism. The catalysts consist of two 42-residue peptides that fold into helix-loop-helix motifs and dimerise. They have previously been shown to recognize anionic and hydrophobic substrates and to follow saturation kinetics. The catalytic entity is a HisH(+)-His pair in a helical segment spaced i, i+4, which can be supplemented by arginines and lysines in the adjacent helix. The binding residues have now been optimized for the catalysis of mono-p-nitrophenyl fumarate hydrolysis and found to vary with the location of the site. The catalytic efficiency of the HisH(+)-His site in helix II in positions 30 and 34 is enhanced by the introduction of arginine and or lysine residues in positions 11 and 15, but not in 8 and 11 or in 15 and 19. The most efficient catalyst using this site, JNIIR11K15, catalyses the reaction with a second-order rate constant of 0.134 M(-1) s(-1) in aqueous solution at pH 5.1 and 290 K. The second-order rate constant is larger than those of the corresponding sites with 'longer' and 'shorter' binding residues. Similar experiments have shown that the efficiency and selectivity of catalysts based on a HisH(+)-11-His-15 site in helix I are enhanced the most by the introduction of Lys-30 and Arg-34.

How fumarase recycles after the malate --> fumarate reaction. Insights into the reaction mechanism

Recycling of yeast fumarase to permit repetition of its reaction chemistry requires two proton transfers and two conformational changes, in pathways that are different in detail but thematically similar in the two directions. In the malate --> fumarate direction, simple anions such as acetate accelerate the fumarate-off step producing E(H(f)), a fumarate-specific isoform that retains the C3R-proton of malate. Fumarate specificity is shown with S-2,3-dicarboxyaziridine, which is competitive vs fumarate and noncompetitive with malate as substrate. The steady-state level of E(H(f)), based on Kii (S-2,3-dicarboxyaziridine), is increased by D2O and decreased by imidazole acting as a general acid for conversion of E(H(f)) to E(H(f))H. E(H(f))H is fumarate-specific as shown by the inhibition pattern with ClO4-. The pKa of this step is approximately 7.25 based on the pH dependence of Kii (ClO4-). A conformational change occurs next as shown by high sensitivity of k(cat) but not k(cat)/Km, to the microviscosogen, glycerol, and change to a nonspecific isoform, E(H(mf))H, probably the same species formed in the fumarate --> malate direction from malate-specific intermediates by a different conformational change. Malate enters the cycle by reaction with E(H(mf))H and returns to E(m)H x malate after a second conformational change. When fumarate-off is slow, as in low anion medium, malate itself becomes an activator of malate --> fumarate. This effect occurs with changes in inhibition patterns suggestive of the bypass of the slow E(f) --> E(mf) conversion in favor of direct formation of E(mf) when free fumarate is formed. 3-Nitro-2-hydroxypropionate, a strong inhibitor of fumarase [Porter, D. J. T., and Bright, H. J. (1980) J. Biol. Chem. 255, 4772-4780] in its carbanion form, is competitive with both malate and fumarate. Therefore, 3-nitro-2-hydroxypropionic acid interacts with E(H(mf))H and not with E(m) or E(f) isoforms. Occurrence of two different conformational changes in the recycling process suggests that the reaction chemistry employs a two-step mechanism. The specificity of inhibition for E(H(mf))H is consistent with the expected intermediate of a carbanion mechanism, E(H)H x carbanion-. The proton transfers and conformational changes of recycling occur in the same sequence that is expected for this reaction chemistry. Several examples of ligand-activated conformational changes are reported.

Fumarate modulates bacterial flagellar rotation by lowering the free energy difference between the clockwise and counterclockwise states of the motor

Switching flagellar rotation from one direction to another is an essential part of bacterial chemotaxis. Fumarate has been shown to possess the capacity to restore to flagella of cytoplasm-free, CheY-containing bacterial envelopes the ability to switch directions and to increase the probability of reversal in intact cells. Neither the target of fumarate action nor the mechanism of function is known. To distinguish between the two potential targets of fumarate, the response regulator CheY and the flagellar switch-motor complex, we compared flagellar rotation between isogenic strains that lacked CheY and had either low or high levels of fumarate. The difference in the fumarate levels was due to a deletion of the genes encoding the enzymes that synthesize and metabolize fumarate; succinate dehydrogenase and fumarase, respectively. The strains were in a gutted background (i.e. a background deleted for the cytoplasmic chemotaxis proteins and some of the receptors), and switching was achieved by carrying out the measurements at 2.5 degreesC, where it has been demonstrated that gutted cells switch spontaneously. The flagellar rotation of the strain with the highest level of fumarate was the most clockwise-biased and had the highest reversal frequency, indicating that fumarate is effective even in the absence of CheY. Fumarate reduced the free energy difference of the counterclockwise-to-clockwise transition and had no appreciable effect on the activation energy of this transition. Similar observations were made at room temperature, provided that intracellular CheY was present. In a wild-type background, both mutants made rings on semi-solid agar typical of normal chemotaxis. Taken together, the results suggest that the target of fumarate is the switch-motor complex, that fumarate acts by increasing the probability of the clockwise state, and that a fumarate level as low as that found in succinate dehydrogenase mutants is sufficient for normal chemotaxis.

Production of L-malic acid via biocatalysis employing wild-type and respiratory-deficient yeasts

The yeast Saccharomyces cerevisiae has been used to efficiently produce L-malic acid from fumaric acid. Fumarase is responsible for the reversible conversion of fumaric and L-malic acids in the TCA cycle. To investigate the function of mitochondrial and cytoplasmic fumarase isoenzymes in L-malic acid bioconversion, a wild-type strain and a cytoplasmic respiratory-deficient mutant devoid of functional mitochondria were employed. The mutant strain, which only contained the cytoplasmic fumarase, was still functional in fumaric acid to L-malic acid bioconversion However, its specific conversion rate was much lower (0.20 g/g.h) than that of the wild-type strain (0.55 g/g.h).

A tricarboxylic acid cycle intermediate regulating transcription of a chloroaromatic biodegradative pathway: fumarate-mediated repression of the clcABD operon

The ortho-cleavage pathways of catechol and 3-chlorocatechol are central catabolic pathways of Pseudomonas putida that convert aromatic and chloroaromatic compounds to tricarboxylic acid (TCA) cycle intermediates. They are encoded by the evolutionarily related catBCA and clcABD operons, respectively. Expression of the cat and clc operons requires the LysR-type transcriptional activators CatR and ClcR, respectively, and the inducer molecules cis,cis-muconate and 2-chloro-cis,cis-muconate, respectively. The regulation of the cat and clc promoters has been well studied, but the extent to which these operons are repressed by growth in TCA cycle intermediates has not been explored. We demonstrate by transcriptional fusion studies that the expression from the clc promoter is repressed when the cells are grown on succinate, citrate, or fumarate and that this repression is ClcR dependent and occurs at the transcriptional level. The presence of these organic acids did not affect the expression from the cat promoter. In vitro transcription assays demonstrate that the TCA cycle intermediate fumarate directly and specifically inhibits the formation of the clcA transcript. No such inhibition was observed when CatR was used as the activator on either the cat or clc template. Titration studies of fumarate and 2-chloromuconate show that the fumarate effect is concentration dependent and reversible, indicating that fumarate and 2-chloromuconate most probably compete for the same binding site on ClcR. This is an interesting example of the transcriptional regulation of a biodegradative pathway by the intracellular sensing of the state of the TCA cycle.

Characterization of partially saturated poly(propylene fumarate) for orthopaedic application

A partially saturated linear polyester based on poly(propylene fumarate) (PPF) was synthesized for potential application in filling skeletal defects. The synthesis was carried out according to a two-step reaction scheme. Propylene glycol and fumaryl chloride were first combined to form an intermediate fumaric diester. The intermediate was then subjected to a transesterification to form the PPF-based polymer. This method allowed for production of a polymer with a number average molecular weight up to 1500 and a polydispersity index of 2.8 and below. The polymeric backbone structure was investigated through the use of FTIR and NMR. Kinetic studies of the transesterification allowed mapping of the molecular weight increase with reaction time. The final product was also characterized by thermal and solubility analysis.

Restructuring the active site of fumarase for the fumarate to malate reaction

Changes in the active site of fumarase (yeast fumarase II) that occur when fumarate is converted to malate (E.F --> E.M) must be reversed for another cycle of reaction to take place. As shown here, recycling of the enzyme includes two proton transfers and one conformational change. These events, together with the M-off step, are variously rate-determining depending on the medium. In very low salt the release of M is limited by the conformational change. Thus, (V/Km)F decreases with increased viscosity, shown with glycerol. A variety of simple anions, such as Cl- at approximately 50 mM and F itself at low concentration, activate the dissociation of M. This nonspecific anion effect is the basis for the >4-fold apparent cooperative activation by substrate. The M-off step and the conformational change are independent and random-order events. Thus, even when M-off is made rapid the rate of recycling is inhibited by glycerol, which in 100 mM NaCl inhibits Vmax but not V/Km. The enzyme form that results when M is released is M-specific, Em. Thus mesotartarate, competitive toward M, is noncompetitive toward F. The slow conformational change required for recycling of Em is activated by Pi and chaotropic anions such as azide and thiocyanate, giving rise to a nonspecific intermediate, Emf (mesotartarate becomes competitive toward F and Britton's countertransport property disappears with these activators). Evidence is presented for the locations and rates of the two proton transfer steps required to complete the cycle.

Effect of polymer foam morphology and density on kinetics of in vitro controlled release of isoniazid from compressed foam matrices

The purpose of this study was to compare the effect of polymer foam morphology and density prior to compaction on the kinetics of isoniazid (INH) release from the final high-density extruded matrices. The feasibility of preparing low density foams of several biopolymers, including poly(L-lactide) (PLLA), poly(glycolide) (PGA), poly(DL-lactide-co-glycolide) (PLGA), poly(gamma-benzyl-L-glutamate) (PBLG), and poly(propylene fumarate) (PPF), via a lyophilization technique was investigated. Low-density foams of PLGA, PBLG, and a mixture of PLGA and PPF were successfully fabricated by lyophilization of the frozen polymer solutions either in glacial acetic acid or in benzene. The morphology of these foams depends on the polymer as well as the solvent used in the fabrication process. Thus, PLGA produces a capillary structure when lyophilized from benzene solution and a leaflet structure from glacial acetic acid, but PBLG yields a leaflet structure from benzene. Matrices were prepared by impregnating these foams with aqueous solutions of INH, removing the water by a second lyophilization, and then compressing the low-density INH containing foams by compaction and high-pressure extrusion. The resulting nonporous matrices had densities of approximately 1.30 g/cm3. In vitro kinetics were in accord with the Roseman-Higuchi diffusion model and demonstrate that release rates depend on the initial foam density, while foam structure has little influence on the release kinetics.

Fumaric acid, anti-thrombin substance from Rhizopus javanicus

An anti-thrombin substance (M2) was isolated from a culture broth of Rhizopus javanicus. Accumulation of M2 reached a maximum peak after 14 to 15 days of incubation and then decreased. The yield of M2 was 500 mg from 1 L of culture broth. M2 inhibited thrombin activity, and its 50% inhibition concentration in a reaction mixture containing 50 microL of 12.5 NIH unit/mL thrombin and 200 microL of 0.33% bovine fibrinogen was 63 microM. M2 had a specific activity for thrombin, but it was less responsive to plasmin, tissue-type plasminogen activator, urokinase, plasma kallikrein and glandular kallikrein. The structure of M2 was identified as fumaric acid by elementary analysis, FAB/MS, 1H-NMR, 13C-NMR and IR spectra.

Schizostatin, a novel squalene synthase inhibitor produced by the mushroom, Schizophyllum commune. I. Taxonomy, fermentation, isolation, physico-chemical properties and biological activities

In the process of screening for squalene synthase inhibitors from microbial fermentation products we have isolated a novel compound, named schizostatin (Fig. 1), from the culture broth of the mushroom, Schizophyllum commune SANK 17785. Schizostatin inhibited rat liver microsomal squalene synthase dose dependently and the IC50 value was 0.84 microM. The inhibition was competitive with respect to farnesylpyrophosphate with a Ki value of 0.45 microM.

Schizostatin, a novel squalene synthase inhibitor produced by the mushroom, Schizophyllum commune. II. Structure elucidation and total synthesis

Schizostatin (1) has been isolated as a potent and selective inhibitor of squalene synthase. Its structure has been determined using spectroscopic methods: the compound is shown to be a diterpenoid which has a trans-dicarboxylic acid moiety. Total synthesis of schizostatin (1) was achieved by the highly regio- and stereoselective coupling reaction of an allylic bromide with a barium reagent. The Z-isomer 16 was also prepared using the stereoselective syn-addition of an organocopper reagent to acetylenedicarboxylate.

Spectral editing in 13C CP/MAS experiments at high magnetic field

We show that the spinning side-bands of protonated and non-protonated carbon atoms can be well separated by means of the standard SCP and LCPD experiments at a relatively slow sample spinning rate or at high magnetic field. These experiments offer a promising way of measuring the principal values of chemical shift anisotropies via spinning side-band analysis in a moderately complex system. General spectral editing in 13C cross-polarization magic-angle spinning (CP/MAS) experiments at high field is achieved by incorporating the total side-band suppression (TOSS) pulse sequence into the standard series of spectral editing pulse sequences. It is confirmed that the relative signal intensity for a certain kind of functional group obtained at different polarization, polarization-inversion and depolarization times is about the same as that obtained at low magnetic field, and that the signal intensity distortion introduced by the TOSS sequence for resonances having different chemical shift anisotropies does not interfere with the spectral editing process. However, quantitative results can only be expected in those cases where full restoration of the intensity of the central band can be achieved by the TOSS sequence. This new strategy at high field is demonstrated by using fumaric acid monoethyl ester as a model compound. A typical application to a Chinese resin is presented, where the relative ratio of each functional group in the aliphatic portion to the total number of aliphatic carbon atoms is determined from only three experimental spectra.

Biodegradable bone cement compositions based on acrylate and epoxide terminated poly(propylene fumarate) oligomers and calcium salt compositions

The synthesis of biodegradable bone cement compositions is presented. These bone cement compositions can be applied as a putty-like mixture and harden to a strong material in a bone fracture. They degrade from the site of application to allow the ingrowth of new bone for complete healing of the bone fracture. The bone cement is composed of a solid particulate phase dispersed in an initially liquid polymeric phase, which can be hardened by cross-linking. The polymeric phase is a low-molecular-weight liquid poly(propylene fumarate) (PPF) containing double bonds available for cross-linking. The solid particulate phase consists of calcium carbonate and tricalcium phosphate. PPF oligomers of Mw = 1800 and Mn = 750 were prepared from the condensation of non-volatile bis(2-hydroxypropyl fumarate) and propylene-bis(hydrogen maleate) trimers. PPF terminated divinyl and diepoxide derivatives were obtained from the reactions between PPF diol and acryloyl chloride or epichlorhydrin, respectively. Putty-like cement compositions were prepared from a mixture of 30 wt% polymer phase containing benzoyl peroxide-dimethyl toluidine as polymerization catalyst and 70 wt% calcium salts. The divinyl and diepoxide terminated PPF oligomers provided a high strength composition of between 30 and 129 MPa which is suitable for bone cement applications. In vitro hydrolysis of the composites showed little weight loss with the compressive strength remaining above 20 MPa after 4 weeks in buffer solution. Compositions of the PPF oligomers cross-linked without calcium salts showed a gradual weight loss (10-65 wt% after 4 weeks) when placed in buffer solution followed by high water absorption (18-200 wt% after 4 weeks), with the epoxide terminated PPF being the least to degrade or absorb water.

High resolution 1H spectra of powdered solids observed by Hahn echo pulse sequence with magic-angle spinning

The 1H magic-angle spinning (MAS) spectrum for a typical powdered solid is composed of a high resolution component and a broadline component. The high resolution component can be well isolated from the broadline component by the Hahn echo sequence with a long echo time. Compared with CRAMPS experiment, which measures the proton system as a whole, the high resolution echo-MAS method measures only a fraction of the solid, which is usually small at room temperature and quite different from the majority of the solid in both molecular motion and chemical environment. It is shown that for a sample of fumaric acid monoethyl ester, the chemical shifts of the high resolution component are apparently distinguishable from the isotropic chemical shifts of the broadline component in the CRAMPS spectrum as the temperature approaches the melting point. In addition, for a sample of malonic acid, the echo-MAS spectrum is sensitive to moisture and temperature, while its corresponding CRAMPS spectrum is not. It is suggested that the molecules which produce the high resolution component are related to the lattice defects in a solid, including the surface disorder of the polycrystallites, while the molecules that generate the broadline component are located on the rigid lattice of the solid.

The use of differential transverse relaxation to detect mobile species in solids

Delayed acquisition of the proton NMR in selected organic molecular solids (L-alanine, durene, ethyl fumarate, and p-hydroxybenzoic acid) is shown to allow the observation of mobile species in the presence of relatively rigid bulk molecules. The mobility is found to be thermally activated. The combination of the thermally activated motion and magic-angle spinning leads to a fraction of these species moving nearly isotropically on the time scale of the inverse of the homonuclear dipolar splitting. In the case of ethyl fumarate and alanine, there exist populations with differing values of T1 and T1 row. This indicates the co-existence of relatively rigid and relatively mobile molecules in the same sample. The intensities under delayed acquisition cannot always be trusted to yield quantitative information. Comparison of spectra taken under delayed acquisition and under the CRAMPS (B.C. Gerstein, R.G. Pembleton, R.C. Wilson and L.M. Ryan, J. Chem. Phys., 66 (1977)361) technique is made.

Analysis of a vinyl pyrrolidone/poly(propylene fumarate) resorbable bone cement

A resorbable bone cement was formulated from N-vinyl-2-pyrrolidinone (VP), the unsaturated polyester poly(propylene fumarate) (PPF), and the inorganic filler tribasic calcium phosphate (hydroxy apatite). Cure, initiated by benzoyl peroxide and accelerated by N,N-dimethyl-p-toluidine, resulted in the formation of VP crosslinks between polyester chains. During cure the cement hardened from a viscous moldable putty to a rigid structure with a shore D hardness of 50-60. The purpose of this study was to determine the fractions of PPF and VP incorporated into the crosslinked structure. Dissolution of the cured cement in water followed by extraction of the residue in tetrahydrofuran indicated that over 90% of the PPF was crosslinked over the range of PPF/VP ratios explored, but that the fraction of VP used in formation of crosslinks depended linearly on the PPF/VP ratio. Kinetic analysis of these data suggests that k'pp/kpf (the reactivity ratio) was approximately 2.0 where k'pp is the rate constant for the addition of VP radical to VP monomer leading to formation of poly(vinyl pyrrolidone), and kpf is for the addition of VP radical to PPF unsaturation.

Importance of historical contingency in the stereochemistry of hydratase-dehydratase enzymes

There are two stereochemical classes of hydratase-dehydratase enzymes. Those that catalyze the addition of water to alpha, beta-unsaturated thioesters give syn addition-elimination stereochemistry, whereas those that catalyze the addition of water to conjugated carboxylate substrates give anti stereochemistry. This dichotomy could reflect different adaptive advantages or contingencies of separate evolutionary histories. Determination of the nonenzymatic stereochemistry of deuterium oxide addition to fumarate and to S-crotonyl N-acetylcysteamine has provided direct evidence for the importance of the contingencies of evolutionary history, rather than chemical efficiency, in the pathways of these hydratase-dehydratase enzymes.

Investigations of glutathione conjugation in vitro by 1H NMR spectroscopy. Uncatalyzed and glutathione transferase-catalyzed reactions

Conjugation reactions of glutathione (GSH) and related thiols with diethyl maleate (DEM) and other alpha, beta-unsaturated carbonyl compounds have been investigated by 1H NMR spectroscopy. The products from the reaction with DEM and diethyl fumarate (DEF) are shown to be the diastereomers of S-(alpha,beta-diethoxycarbonylethyl)glutathione. During the course of the reaction, DEM isomerized to DEF, and the rate of isomerization was dependent upon whether the solvent was 1H2O or 2H2O. The observed rate data exhibit apparent second order kinetic behavior. The reaction of maleate with GSH was considerably slower, and solvent-dependent isomerization was observed, while little reaction of fumarate with GSH was observed at pH 6.5. Reaction of DEM with N-acetyl-L-cysteine followed a similar course to that of GSH, and although L-cysteine reacted rapidly with DEM, it did not promote the isomerization of DEM. Reactions involving penicillamine and N-acetylpenicillamine were considerably slower. Conjugation reactions catalyzed by commercial GSH transferases and selected rat and human purified isoenzymes were also investigated. Of those isoenzymes studied, rat GSH transferase 4-4 was found to exert the greatest degree of stereo control in conjugation reactions with DEF.

Derivatization of a new poly(ether urethane amide) containing chemically active sites

A novel poly(ether urethane amide) was synthesized by chain-extending the prepolymer with fumaric acid, resulting in a polymer exhibiting superior mechanical properties and containing chemically active derivatization sites, stemming from the fumaramide double bond. The derivatization of the active sites was performed via a Michael-like addition of amine-terminated poly(ethylene oxide) chains, which when performed in bulk, greatly affected the mechanical properties of the polymer, except in the case in which a relatively high molecular weight was grafted. Surface grafting of the polymer led to a significantly lower effect on its mechanical properties, which was minimal when a high molecular weight molecule was used.

Purification and properties of crystalline 3-methylaspartase from two facultative anaerobes, Citrobacter sp. strain YG-0504 and Morganella morganii strain YG-0601

3-Methylaspartase (3-methylaspartate ammonia-lyase, EC 4.3.1.2) from two facultative anaerobes from soil, Citrobacter sp. strain YG-0504 and Morganella morganii strain YG-0601, were purified and crystallized from their crude extracts. Both of the Citrobacter and Morganella enzymes appeared to be a dimer of subunits of M(r) 40,000 and 44,000, respectively. The enzymes had similar enzymological properties: optimum pH for the deamination reaction of (2S,3S)-3-methylaspartic acid, substrate specificity, inhibitor, divalent and monovalent cation requirement, and N-terminal amino acid sequence homology. However, some differences were detected in pH and temperature stability, optimum pH for the amination reaction of mesaconic acid, optimum temperature, specific activity, and stability during electrophoresis. Both enzymes had similar enzymological properties to the known 3-methylaspartase from an obligate anaerobic bacterium, Clostridium tetanomorphum H1, except kinetic constants and substrate specificities.

Constrained search of conformational hyperspace of inactivators of glucosamine-6-phosphate synthase

Glucosamine-6-phosphate (GlcN-6-P) synthase (EC 2.6.1.16) is a key enzyme in amino sugar metabolism in micro-organisms and its selective and irreversible inhibitors can become valuable antifungal drugs. We performed a constrained search of the conformational hyperspace of glutamine and of the set of specific inactivators of the enzyme, as well as of some non-specific inhibitors of many cysteine containing enzymes. From these calculations we obtained spatial relationships of functional groups, the presence and specific orientation of which in the active site of the enzyme is important for effective and selective action of the inhibitor. Subsequent quantum chemical calculations confirmed the correctness of the pharmacophore conformation we obtained. Pharmacophore conformation of FMDP molecule, the most potent inhibitor in the selective inhibitors group, is placed close to the energy minimum on the conformational energy map.