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The catalytic pathway of class A beta-lactamases involves an acyl-enzyme intermediate where the substrate is ester-linked to the Ser-70 residue. Glu-166 and Lys-73 have been proposed as candidates for the role of general base in the activation of the serine OH group. The replacement of Glu-166 by an asparagine in the TEM-1 and by a histidine in the Streptomyces albus G beta-lactamases yielded enzymes forming stable acyl-enzymes with beta-lactam antibiotics. Although acylation of the modified proteins by benzylpenicillin remained relatively fast, it was significantly impaired when compared to that observed with the wild-type enzyme. Moreover, the E166N substitution resulted in a spectacular modification of the substrate profile much larger than that described for other mutations of Omega-loop residues. Molecular modeling studies indicate that the displacement of the catalytic water molecule can be related to this observation. These results confirm the crucial roles of Glu-166 and of the "catalytic" water molecule in both the acylation and the deacylation processes.

Bacterial resistance to beta-lactam antibiotics, a clinically worrying and recurrent problem, is often due to the production of beta-lactamases, enzymes that efficiently hydrolyze the amide bond of the beta-lactam nucleus. Imipenem and other carbapenems escape the activity of most active site serine beta-lactamases and have therefore become very popular drugs for antibacterial chemotherapy in the hospital environment. Their usefulness is, however, threatened by the appearance of new beta-lactamases that efficiently hydrolyze them. This study is focused on the structure and properties of two recently described class A carbapenemases, produced by Serratia marcescens and Enterobacter cloacae strains and leads to a better understanding of the specificity of beta-lactamases. In turn, this will contribute to the design of better antibacterial drugs. Three-dimensional models of the two class A carbapenemases were constructed by homology modeling. They suggested the presence, near the active site of the enzymes, of a disulfide bridge (C69-C238) whose existence was experimentally confirmed. Kinetic parameters were measured with the purified Sme-1 carbapenemase, and an attempt was made to explain its specific substrate profile by analyzing the structures of minimized Henri-Michaelis complexes and comparing them to those obtained for the "classical" TEM-1 beta-lactamase. The peculiar substrate profile of the carbapenemases appears to be strongly correlated with the presence of the disulfide bridge between C69 and C238.

The catalytic properties of six "natural" mutants of the TEM-1 beta-lactamase have been studied in detail, with special emphasis on their activity versus third-generation cephalosporins. On the basis of the recently determined high-resolution structure of the wild-type enzyme, and of the substrates' structures optimized by the AMI quantum chemistry method, we have attempted to explain the influences of the mutations on the substrate profiles of the enzymes. Some of the kinetic results have thus received a satisfactory, semi-quantitative interpretation, especially in the case of single mutations. Analysis of the double mutants proved more hazardous. Extending the comparison to some other class A beta-lactamases showed that similar properties could result from different sequences, supplying an interesting example of convergent evolution within a generally diverging family.

The chance discovery by Fleming in 1928 of a metabolite produced by Penicillium notatum which exhibited bacteriolytic properties was followed by the heroic efforts of the Oxford group of Chain and Florey to isolate and identify the active molecule. This led to the introduction of benzylpenicillin in clinical trials about 50 years ago, probably one of the major breakthroughs in modern chemotherapy. Although some pathogenic bacteria were rapidly recognized as resistant to the new wonder drug, it was believed that a nearly ideal solution had been found to the problem of bacteria-mediated infectious diseases. Indeed, penicillin was extremely efficient and nearly completely innocuous to eukaryotic cells, which allowed the utilization of relatively high doses with little or no unwanted secondary effects. However, in the early 1950s, resistant strains started to appear in generally sensitive species such as Staphylococcus aureus and this phenomenon initiated a constant struggle between chemists, biochemists and microbiologists, on the one side, and bacteria, on the other. The former continuously isolated new molecules from natural sources and synthesized additional compounds, while the latter kept devising new strategies to escape the lethal action of an ever expanding arsenal of drugs which exhibited one common chemical characteristic: the presence of the four-membered β-lactam ring shown in Fig. 1 (together with some members of the β-lactam family).

Trauma is the cause of 5 to 10% of all cases of osteoarthritis of the hip. One third of patients with a dislocation or fracture-dislocation of the hip or an acetabular fracture develop osteoarthritis of the hip within one to 20 years. Symptoms may be minor or absent during the interval. In addition to severe injuries, simple contusions resulting for instance from a blow to the greater trochanter or knee or from forced abduction of the hip (e.g., splits) can also result in osteoarthritis of the hip. We developed a set of five imputability criteria, of which three are essential: 1) documentation of the exact nature of the trauma; 2) absence of osteoarthritis in the uninjured hip; 3) consistency between the estimated duration of osteoarthritis and the date of the injury. Causality assessment problems which arise when a trauma worsens or accelerates preexisting osteoarthritis are discussed on the basis of clinical and roentgenographic findings. Mechanical and biochemical factors involved in the pathophysiology of contusion-related osteoarthritis of the hip are briefly reviewed.

The main Indices of Quality of Life used in rheumatology and their aims and applications are surveyed. Their use in osteoarthritis implies a few issues that are addressed in a critical manner. Indices of Quality of Life are useful to measure deficiency resulting from osteoarthritis by comparison with other rheumatic diseases, as rheumatoid arthritis, connective tissue diseases, fibromyalgia... They are sensitive enough for apraising the domains improved by a radical treatment such as joint replacement. However, their scores are only slightly changing in most of the drug trials, in which the more simple functional indices seem demonstrative enough. Last but no least, they are notably time consuming for both the patient and the physician.

Etude de la chimisorption a 100°K, 140°K et 300°K sur La 2 O 3 modifie par un traitement thermique (500°-1200°K)

Crystals of A2ZnCl4 or A2CoCl4, with A = K, NH4 or Rb, belong to the orthorhombic system. Lattice parameters, indices and spacings are tabulated for the whole series. All these crystals are isotypic with β-K2SO4.

Oxidation of benzisothiazole by hydrogen peroxide leads to saccharine, but the same reaction with benzisoselenazole does not lead to selenosaccharine. The product of this oxidation is the ammonium o-carboxybenzeneselenonate monohydrate. Crystals are triclinic, P1, with a =6.243, b =7.598 and c =12.457 A, α =142.38, β = 104.98 and γ = 85.47°, and Z = 2. The refinement led to a final R-value of 0.056. The ammonium ion and water molecule coordinations are discussed in terms of hydrogen bonds. The coordination of the selenium atom is also described.

Beta-lactamases are responsible for resistance to penicillins and related beta-lactam compounds. Despite numerous studies, the identity of the general base involved in the acylation step is still unclear. It has been proposed, on the basis of a previous pKa calculation and analysis of structural data, that the unprotonated Lys73 in the active site could act as the general base. Using a continuum electrostatic model with an improved treatment of the multiple titration site problem, we calculated the pKa values of all titratable residues in the substrate-free TEM-1 and Bacillus licheniformis class A beta-lactamases. The pKa of Lys73 in both enzymes was computed to be above 10, in good agreement with recent experimental data on the TEM-1 beta-lactamase, but inconsistent with the proposal that Lys73 acts as the general base. Even when the closest titratable residue, Glu166, is mutated to a neutral residue, the predicted downward shift of the pKa of Lys73 shows that it is unlikely to act as a proton abstractor in either enzyme. These results support a mechanism in which the proton of the active Ser70 is transferred to the carboxylate group of Glu166.

The maximum wavelength λd - d of the transition between d orbitals of tetrachlorocuprates depends on the deformation D of the CuCl42- tetrahedron in these crystals. On the basis of their experimental absorption spectra, the relation between λd - d and D is given for many tetrachlorocuprates so that the symmetry of the CuCl42- ion can be predicted in some other crystals on the basis of the position of the d-d transition.

C22H26C12N204, monoclinic, P2~, a = 10.382 (1), b = 11.688 (1), c = 9.325 (1) /k, fl -109.03 (2) °, Z = 4, V = 1069.7 A3, p(CuKa)= 3-007 mm -], D x = 1.407 Mg m -a, M r = 453.37. The structure has been refined to R = 0.057 on 1941 observed reflections. The conformation of the molecule is similar to those observed in other aspidospermine compounds. There is only one short intermolecular distance, of 3.385/k between O(1) and Cl(2). Introduct ion. La (-)-tabersonine (Fig. 1), trait6e en milieu m6thanolique par un 6quivalent d'acide chlorhydrique et deux +quivalents d'acide mdta-chloroperbenzo'ique (MCPB) conduit, par r6arrangement oxydatif, au compos~ de la Fig. 2 (Lewin, Rolland & Poisson, 1979). Ce dernier est un d6riv6 de la (+)-vincamine, alcalo'ide naturel actuellement utilis~ en th6rapeutique comme oxyg&nateur c6r+bral. Par contre, si la (-)-tabersonine est mise en r6action dans le m~thanol avec deux 6quivalents d'acide chlorhydrique et trois +quivalents de MCPB, on isole un compos+ tr+s diff6rent de (2) et qui, par rapport la (-)-tabersonine, a fix6 deux atomes de chlore sur le noyau aromatique, un atome d'oxyg+ne et les 616merits d'une molecule de m+thanol sur le reste de la mol&cule. Au vu des spectres usuels (UV, IR, RMN de IH et de ~3C, spectre de masse), la formule de la Fig. 3 peut ~tre envisag~e pour ce d+riv6. Cependant, afin de confirmer cette hypoth6se, nous avons 6t~ amends/l d6terminer Ia structure de ce d~riv& Les cristaux obtenus dans l'ac~tone nous ont ~t~ fournis par l'Omnium Chimique (Bruxelles, Belgique). Les 2003 intensit&s mesur~es sur un diffractom+tre fi, quatre cercles Hilger & Watts ont subi les corrections de Lorentz et de polarisation. L'application du programme MULTAN 77 (Main, Lessinger, Woolfson, Germain & Declercq, 1977) a r+v+l+ tous les atomes non hydrog+ne. Les coordonn~es atomiques ont ensuite ~t~ affin+es dans l'approximation de blocs diagonaux, avec des facteurs 0567-7408/80/010196-03501.00 de temperature anisotrope, jusqu'fi un indice r6siduel de 5,7% pour 1941 r&flexions consid&r+es comme observ6es [I > 20(I)]. Les positions des atomes d'hydrog+ne ont 6t6 introduites dans les calculs, mais pas dans l'affinement. Le schema de pond6ration utilis6 est celui de Cruickshank (1961). Dans les derniers cycles d'affinement, on a tenu compte de l'effet de diffusion anomale pour les atomes de CI et d'O. Les coordonn~es atomiques finales sont

For some crystals, the structures of which have already been determined, the flattening, D, of the CuCl42- tetrahedra has been estimated. The paramagnetic susceptibilities of many tetrachlorocuprates have been measured by the Faraday method. The mean magnetic moment decreases linearly as D increases, if D is greater than 0.2. From the known mean magnetic moment, it is therefore possible to estimate the D value of the CuCl42- tetrahedron.

The isolated or predominant geodes of the femoral head without signs of coxarthritis or coxitis, seem to form in response to: osteochondritis dissecans in 9 cases where the sequester was only visible in profile films or oblique images for 5 cases, and only at time of operation in 2 cases; incipient necrosis in 3 adult cases, not evidenced in frontal films and only seen in profile films with the patient under axial traction; femoral head dysmorphia in 6 cases among which were 4 polyepiphyseal dysplasias and 2 coxa plana without radiographically apparent sequesters; induced increased pressure caused by congenital subluxation or a major disorder of posture and locomotion of lower limbs in 3 cases. In 2 cases no classification could be assigned to isolated or predominant geodes of the femoral head in spite of anatomic examination. The diagnosis of these isolated or predominant geodes of the head of the femur necessitates excellent films made from different angles of view (profile, "false" profile, usual profile, sometimes oblique shots, tomograms) and often enough a biopsy which must be obtained directly through the joint, not transcervically through the neck if a reliable specimen is desired. The surgical treatment indicated is voiding and packing to a maximum the geodes possibly correcting the former increased pressure discordance. But, in lots of cases the intensity of pain and discomfort remains moderate for years, so indication for surgery arises late after onset.

Three-dimensional electrostatic maps were calculated for six potent antagonists of platelet-activating factor (PAF), the antagonists being selected for their apparent structural heterogeneity. The molecules examined were the compact Ginkgolides BN 52020, BN 52021 and BN 52022 (1, 2 and 3), the semi-rigid kadsurenone (4), a flexible synthetic dinor type C furanoid lignan L-652,731 (5a) and the triazolothienobenzodiazepine WEB 2086 (7). Calculation of the electrostatic potential generated around all the above molecules showed the existence of two wells of negative potential or 'cache-oreilles' (ear-muffs), i.e., the isocontours drawn at -10 kcal/mol, located at 180 degrees from each other and separated by a maximum distance of 22-27 A. Except for the synthetic dinor type C furanoid lignan (5a), the molecules also presented a moderate hydrophobic fragment, which constitutes a third point of interaction with the high-affinity binding site in rabbit and human platelets. The findings of the present study allow speculation that this high-affinity acceptor site may be a 'polarized cylinder' with a diameter of 10-12 A.

From the roots of Strychnos icaja Baill. an unsymmetrical dimeric alkaloid has been isolated and called sungucine. Its original structure has been established by X-Ray diffraction; UV, IR, MS and NMR data are also given.

Dissociative adsorption of H2 on ZnO, apart from the bands due to OH and ZnH stretching vibrations, gives rise to bands at ca. 840 and 810 cm–1 which can be attributed to the bending modes of these surface structures. Analysis of the integrated intensities of the bands arising after H2 and HD adsorption at 100 and 300 K shows that both the 840 and 810 cm–1 bands are due to ZnOH group vibrations. Their shift after 18O isotope substitution of surface oxygen, only 1 and 2 cm–1, respectively, implies that they cannot be associated with the Zn—O vibration or its overtone enhanced by Fermi resonance. They should be attributed to two bending modes of surface hydroxyls. After HD and D2 adsorption a band for the OD bending vibration was detected at 637 cm–1. In accordance with these data, νOH(D)+δOH(D) combinations were observed at 4297 and 3195 cm–1, which give the values of 807 and 611 cm–1 for δOH and δOD, corresponding, apparently, to the more intense low-frequency component.