Regioselectivity of the enzymatic transgalactosidation of D- and L-xylose catalysed by beta-galactosidases

The regioselectivity of enzymatic transgalactosidation depends on the source of the beta-galactosidase used. When the galactosyl acceptor only contains secondary hydroxyl groups, e.g., D- or L-xylose, it is possible to find an enzyme that catalyses preferentially the synthesis of any of the three regioisomers 4-, 3- and 2-O-beta-D-galactopyranosyl-D-xylose (1, 2 and 3, respectively) or 4-, 3- and 2-O-beta-D-galactopyranosyl-L-xylose (4, 5 and 6, respectively). Enriched mixtures in 1, 2 or 3 were obtained using beta-galactosidases from Escherichia coli, bovine testes or Aspergillus oryzae, respectively, by transgalactosidation reaction of O-nitrophenyl-beta-D-galactopyranoside and D-xylose, and enriched mixtures in 4, 5 or 6 were obtained in a similar way using beta-galactosidases from Aspergillus oryzae, lamb small-intestine (intestinal lactase-phloridzin hydrolase) or Saccharomyces fragilis, respectively, using L-xylose as acceptor.     

Chemical oxidation and DNA damage catalysed by inorganic sunscreen ingredients

To date there have been fewer than a dozen studies on the nature of, and contributory factors in, critical incidents (CI) in anaesthesia. The first of these, by Cooper and colleagues, showed that the vast majority of their CI involved human error [1]. Most recently, the on-going Australian Incident Monitoring Study (AIMS), with now more than 2000 reports, has shows that aspects of 'system failure' may constitute the bulk of the contributory factors, even though some human error may be detected in about 80% of the analysed cases [2]. We set up a Critical Incident Reporting System (CIRS) to collect anonymous CI in anaesthesia using a reporting form on the Internet. CIRS analysis of the first 60 cases corroborates the findings of previous CI studies. In addition, our preliminary results have shown certain important trends, especially those concerning the contributory factor of communication in the Operating Theatre. Although to date we are unable to assess the educational importance of these CI reports, we believe that there is great potential for this aspect of CIRS.     

Polymerase chain reaction: a link to the future

Polymerase chain reaction (PCR) is a multi-faceted technology that is advancing disease detection. For pathology and clinical laboratories, PCR will be the tool of choice into the next century as scientists continue to develop and refine new uses. An amazingly simple process that amplifies nucleic acid sequences, PCR will change the practice of medicine because it will play a role in all aspects of the patient care continuum from diagnosis to treatment monitoring. Some striking applications range from detecting infectious and inherited diseases to assessing pharmacologic interventions. Additionally, the remarkable sensitivity of PCR will allow determination of a patient's genetic predisposition to diseases, thereby improving prevention modalities. Thus, medical practitioners should gain a basic understanding of this phenomenal cornerstone of molecular diagnostics. This article briefly reviews the history, theory, and uses of PCR and discusses relevant applications for military medicine.     

Ferriprotoporphyrin catalysed decomposition of artemether: analytical and pharmacological implications

The ability of the products of erythrocytic haemolysis and ferriprotoporphyrin (FP-IX)-containing substances of facilitate the decomposition of the antimalarial drug artemether has been evaluated in vitro. The products of haemolysis accelerate the degradation of artemether to unidentified compounds which are undetectable by currently available HPLC methods. This decomposition is temperature dependent and occurs after relatively brief artemether (ARM)-catalyst contact. Using radiolabelled [16-14C]ARM, we have demonstrated that the extractability of total radioactivity into the organic phase diminishes with increasing FP-IX concentration with an appreciable reduction in the organic extractability as ARM in the presence of FP-IX and associated increase in water solubility of radioactivity when the concentration of FP-IX increases from 0 to 7.7 mM. This effect appears to be temperature dependent for incubations with haematin. Characterisation of the organically extractable radioactivity from incubations of [16-14C]ARM with FP-IX has shown a loss of ARM and the formation of two radioactive products which occurs in proportion to the concentration of FP-IX. We believe these findings are of particular relevance to the determination of plasma concentrations of ARM and dihydroartemisinin (DHA) in malaria patients where extensive haemolysis and the presence of breakdown products of haemoglobin may contribute to a reduction in the circulating concentration of these substances. In these circumstances, measurement of ARM and DHA by conventional methods may be meaningless.     

Molecular modeling of the enantioselectivity in lipase-catalyzed transesterification reactions

Two strategies based on the use of subsets for calculating the enantioselectivity in lipase-catalyzed transesterifications using the CHARMM force field were investigated. Molecular dynamics was used in our search for low energy conformations. Molecular mechanics was used for refining these low energy conformations. A tetrahedral intermediate with a rigid central part was used for mimicking the transition state. The energy differences between the transition states of the diastereomeric enzyme-substrate complexes were calculated. The way of defining the subsets was based on two fundamentally different strategies. The first strategy used predefined parts of the enzyme and the substrate as subsets. The second approach formed energy-based subsets, varying in size with the substrates studied. The selection of residues to be included in these energy-based subsets was based on the energy of the interaction between the specific residue or water molecule and the transition state. The reaction studied was the kinetic resolution of secondary alcohols in transesterifications using the Candida antarctica lipase B as chiral biocatalyst. The secondary alcohols used in the study were 2-butanol, 3-methyl-2-butanol, and 3,3-dimethyl-2-butanol.     

Formyl phosphate: a proposed intermediate in the reaction catalyzed by Escherichia coli PurT GAR transformylase

The Escherichia coli purT encoded glycinamide ribonucleotide transformylase (GAR transformylase) serves as an alternate enzyme in the production of formyl GAR for use in de novo purine biosynthesis. This enzyme differs from the previously known purN encoded enzyme in size, sequence, and substrates; ATP and formate are required as opposed to formyl tetrahydrofolate. Kinetic studies of the wild-type PurT enzyme described here demonstrate that formyl phosphate behaves as a chemically and kinetically competent intermediate. The requirement for ATP and GAR in these reactions is consistent with previous steady-state kinetic results, which demonstrated that all substrates must be bound before catalysis. Kinetic characterization of a mutant, which releases formyl phosphate into solution, and positional isotope exchange studies also support the assignment of formyl phosphate as a plausible intermediate.     

The sulphoxidation of thioanisole catalysed by lactoperoxidase and Coprinus cinereus peroxidase: evidence for an oxygen-rebound mechanism

Using both stopped-flow and conventional spectroscopy, the oxygenation of methyl phenyl sulphide by both lactoperoxidase (LPO) and Coprinus cinereus peroxidase (CiP) was monitored. Controlled continuous addition of H2O2 during turnover and monitoring the presence of native enzymes, compounds I, II and III, led to formation of the sulphoxide in high yield and enantioselectivity. Under those conditions, LPO catalysed the formation of (R) methyl phenyl sulphoxide with a yield of 85% and an enantiomeric excess (e.e.) of 80%. CiP catalysed the formation of (S) methyl phenyl sulphoxide with a yield of 84% and an e.e. of 73%. The enantioselective performance was markedly influenced by the purity of the enzymes used. Presence of compound III during turnover led to rapid inactivation of the peroxidases and, therefore, to both a lower yield of the sulphoxides and a lower enantioselectivity. Stopped-flow kinetic data show that, for both LPO and CiP, the transition of compound I to compound II depends on the concentration of the methyl phenyl sulphide, suggesting an oxygen-rebound mechanism. In line with this mechanism, a methyl phenyl sulphide radical cation was detected by EPR during turnover for LPO.     

Hypochondriasis in the elderly: a reaction to social stress

Hypochondriasis in the elderly is often a preventable or reversible syndrome. It can become chronic if the patient finds no relief from social stress or becomes dependent upon medical services as a source of support. When this is recognized, psychotherapeutic intervention is necessary. Although no socioeconomic group is exempt, hypochondriasis in the elderly occurs more often among the lower social classes. Its higher prevalence in this group is attributable to the frequency and severity of social stress and the loss of alternative social opportunities. If psychotherapeutic intervention is necessary, the elderly hypochondriac patient should be helped to recognize social stress as a major source of the problem and to develop a realistic method of coping with it. Apparently the precipitating factors are often in the socioeconomic sphere; hence, social planners should be aware of this fact if the demands on the health care system are to be reduced.     

The reaction pathway of the isomerization of D-xylose catalyzed by the enzyme D-xylose isomerase: a theoretical study

Different pathways of the metal-induced isomerization of D-xylose to D-xylulose are investigated and compared in detail using energy minimization and molecular dynamics simulation. Two theoretical models are constructed for the reaction: in vacuum and in the enzyme D-xylose isomerase. The vacuum model is constructed based on the X-ray structure of the active site of D-xylose isomerase. It contains the atoms directly involved in the reaction and is studied using a semi-empirical molecular orbital method (PM3). The model in the enzyme includes the effects of the enzyme environment on the reaction using a combined quantum mechanical and molecular mechanical potential. For both models, the structures of the reactants, products, and intermediate complexes along the isomerization pathway are optimized. The effects of the position of the "catalytic Mg2+ ion" on the energies of the reactions are studied. The results indicate: 1) in vacuum, the isomerization reaction is favored when the catalytic metal cation is at site A, which is remote from the substrate; 2) in the enzyme, the catalytic metal cation, starting from site A, moves and stays at site B, which is close to the substrate; analysis of the charge redistribution of the active site during the catalytic process shows that the metal ion acts as a Lewis acid to polarize the substrate and catalyze the hydride shift; these results are consistent with previous experimental observations; and 3) Lys183 plays an important role in the isomerization reaction. The epsilon-NH3+ group of its side chain can provide a proton to the carboxide ion of the substrate to form a hydroxyl group after the hydride shift step. This role of Lys183 has not been suggested before. Based on our calculations, we believe that this is a reasonable mechanism and consistent with site-directed mutation experiments.     

Trisaccharide synthesis by glycosyl transfer from p-nitrophenyl beta-D-N-acetylgalactosaminide on to disaccharide acceptors catalysed by the beta-N-acetylhexosaminidase from Aspergillus oryzae

The beta-N-acetylhexosaminidase from Aspergillus oryzae catalysed the transfer of beta-D-N-acetylgalactosaminyl residues from p-nitrophenyl beta-D-N-acetylglucosaminide on to disaccharide acceptors consisting of thioethyl glycosides of alpha-D-Glc-(1-->4)-beta-D-Glc, beta-D-Glc-(1-->4)-beta-D-Glc and beta-D-Glc-(1-->6)-beta-D-Glc. The principle of 'anomeric control' was exemplified by the results which showed that an alpha-linkage between the units of the acceptor favoured exclusively the formation of a new (1-->4)-linkage, whereas the beta-configuration in the acceptor led to a mixture of (1-->4)- and (1-->3)-linked products, as observed for simple glycosides of monosaccharide acceptors. With the thioethyl beta-lactoside as acceptor, beta-D-Gal-(1-->6)-beta-D-Gal-(1-->4)-beta-D-GlcSEt was formed, owing to the action of residual beta-D-galactosidase activity in the N-acetylhexosaminidase on the thioethyl beta-lactoside acting as both donor and acceptor.     

Phosphoryl transfer reaction regulated by amino acid side chains: a model for phosphoproteins

STUDY OBJECTIVE: To compare the safety and effectiveness of 0.25 mg divided doses of mivacurium chloride to succinylcholine for a 90-second tracheal intubation. DESIGN: Randomized, double-blind, multicenter study in two groups. SETTING: Operating rooms at four university medical centers. PATIENTS: 200 healthy ASA status I and II adult patients scheduled for elective surgery with general anesthesia and endotracheal intubation. INTERVENTIONS: Patients were premedicated with 1 to 2 mg midazolam and 2 micrograms/kg fentanyl. Anesthesia was induced with 2 mg/kg propofol. Group A received 0.25 mg/kg mivacurium given as a divided dose (0.15 mg/kg followed in 30 seconds with 0.1 mg/kg). Group B (control) received 1.5 mg/kg succinylcholine (SCh) preceded two minutes earlier by 50 micrograms/kg d-tubocurarine (dtc). MEASUREMENTS AND MAIN RESULTS: Tracheal intubation grading, train-of-four response of the adductor pollicis, heart rate (HR), and mean arterial blood pressure (MAP) were measured and evaluated. Chi-square analysis was performed for comparison between Group A and Group B with respect to the frequency distribution of intubation using the scores excellent, good, and poor and not possible (combined). Group B had a significantly higher excellent score of intubation than Group A, 84% versus 56% (p < 0.0001). No significant difference was found between the two groups when the scores excellent and good were combined (Fisher's Exact test, p = 0.28). The changes in MAP and HR were similar for the two groups. CONCLUSIONS: When Sch is not desirable, mivacurium 0.25 mg/kg given as a divided dose provides good to excellent intubation conditions 90 seconds after the initial dose without significant changes in MAP or HR. It can be an appropriate alternative for short surgical procedures. It must be emphasized that this conclusion does not apply to rapid-sequence induction-intubation.     

A distinctive cutaneous reaction pattern indicative of infection by reactive arthropathy-associated microbial pathogens: the superantigen ID reaction

The two major cutaneous expressions of infective states are infections of the skin by viable organisms and immunological responses to nonviable microbial antigens or, in the case of molecular mimickry, their human analogues. These immunological responses are designated as cutaneous id reactions, and manifest a histomorphology similar to that seen at the primary infective site. This study presents the clinical and histological findings in 16 patients who developed skin eruptions associated with extracutaneous or systemic infections. There was a striking female predominance; patients ranged in age from 10 to 78 years. The majority of cases manifested skin lesions which clinically resembled Sweet's syndrome, erythema multiforme and/or erythema nodosum. Fever, arthralgia, oligoarthritis, mucosal ulcers of the mouth and/ or genital tract and uveitis were additional features in some cases. Isolated clinical presentations included a petechial rash in a stocking and glove distribution, papular dermatitis, a morbilliform eruption and annular erythema. Among the medical and family histories were atopy and stigmata associated with connective tissue disease (CTD). Two patients were ingesting drugs with known immune dysregulating properties. Skin biopsies showed focal lymphocytic interface dermatitis, a diffuse interstitial histiocytic infiltrate, and a mononuclear cell predominant vascular reaction which in some cases represented vasculitis by virtue of manifesting concomitant luminal or mural fibrin deposition. Eosinophils, eczematous alterations, and papillary dermal edema were identified in a minority of cases. All patients had evidence of a prior or concurrent infection, based on either positive IgM serology for specific microbes or cultures. Among the implicated pathogens were cytomegalovirus, parvovirus B19, streptococcus, mycoplasma, klebsiella, and Borrelia burgdorferi. All of these organisms are among those associated with reactive arthritis, a phenomenon that was seen in some cases. The histology suggested florid cell mediated immunity (CMI), which the authors attributed to the superantigen properties held by the aforesaid pathogens. Skin lesions and constitutional symptoms resolved quickly with antimicrobial therapy in 7 of 9 cases causally linked to bacteria. Spontaneous resolution occurred in 5 of 6 virally mediated eruptions. The other 4 patients were given topical steroids or prednisone; these included 1 patient with Borrelia burgdorferi infection and 1 patient with radiographic evidence of pneumonia who was never cultured, 1 patient with parvovirus B19 infection, and 1 patient with pneumococcal pneumonia and concomitant sarcoidosis. It is the authors' belief that the eruptions seen in these patients may in part reflect a genetic or iatrogenic predisposition to respond excessively to certain infectious triggers.     

Enzyme kinetic modelling as a tool to analyse the behaviour of cytochrome P450 catalysed reactions: application to amitriptyline N-demethylation

1. To determine kinetic parameters (Vmax, K(m)) for cytochrome P450 (CYP) mediated metabolic pathways, nonlinear least squares regression is commonly used to fit a model equation (e.g., Michaelis Menten [MM]) to sets of data points (reaction velocity vs substrate concentration). This method can also be utilized to determine the parameters for more complex mechanisms involving allosteric or multi-enzyme systems. Akaike's Information Criterion (AIC), or an estimation of improvement of fit as successive parameters are introduced in the model (F-test), can be used to determine whether application of more complex models is helpful. To evaluate these approaches, we have examined the complex enzyme kinetics of amitriptyline (AMI) N-demethylation in vitro by human liver microsomes. 2. For a 15-point nortriptyline (NT) formation rate vs substrate (AMI) concentration curve, a two enzyme model, consisting of one enzyme with MM kinetics (Vmax = 1.2 nmol min-1 mg-1, K(m) = 24 microM) together with a sigmoidal component (described by an equation equivalent to the Hill equation for cooperative substrate binding; Vmax = 2.1 nmol min-1 mg-1, K' = 70 microM; Hill exponent n = 2.34), was favoured according to AIC and the F-test. 3. Data generated by incubating AMI under the same conditions but in the presence of 10 microM ketoconazole (KET), a CYP3A3/4 inhibitor, were consistent with a single enzyme model with substrate inhibition (Vmax = 0.74 nmol min-1 mg-1, K(m) = 186 microM, K1 = 0.0028 microM-1). 4. Sulphaphenazole (SPA), a CYP2C9 inhibitor, decreased the rate of NT formation in a concentration dependent manner, whereas a polyclonal rat liver CYP2C11 antibody, inhibitory for S-mephenytoin 4'-hydroxylation in humans, had no important effect on this reaction. 5. Incubation of AMI with 50 microM SPA resulted in a curve consistent with a two enzyme model, one with MM kinetics (Vmax = 0.72 nmol min-1 mg-1, K(m) = 54 microM) the other with 'Hill-kinetics' (Vmax = 2.1 nmol min-1 mg-1, K' = 195 microM; n = 2.38). 6. A fourth data-set was generated by incubating AMI with 10 microM KET and 50 microM SPA. The proposed model of best fit describes two activities, one obeying MM-kinetics (Vmax = 0.048 nmol min-1 mg-1, K(m) = 7 microM) and the other obeying MM kinetics but with substrate inhibition (Vmax = 0.8 nmol min-1 mg-1, K(m) = 443 microM, K1 = 0.0041 microM-1). 7. The combination of kinetic modelling tools and biological data has permitted the discrimination of at least three CYP enzymes involved in AMI N-demethylation. Two are identified as CYP3A3/4 and CYP2C9, although further work in several more livers is required to confirm the participation of the latter.     

The equine endometrial cup reaction: a review

The function of eCG in equine pregnancy is far from clear but it has become evident that eCG has little or no FSH activity in the horse and is therefore probably not responsible for the secondary ovulations. eCG does have luteotrophic activity and it could play a role in the resurgence of the primary corpus luteum (1,7,44). Some evidence exists that the receptor population on the equine gonads is heterogenous in a way that makes it possible to distinguish eCG from eLH, resulting in different post-receptor effects (7). There is also evidence that eCG itself is heterogenous, both in glycosylation and in primary structure, not only between different individual animals but also within one animal during different stages of gestation. The differences could simply reflect the difference between stored and secreted hormone, but on the other hand the release of different eCG forms could be under endocrine control, allowing the mare to produce forms appropriate to specific biological needs (74). Thus some forms of eCG could play a role in immunological events taking place at the foeto-maternal interface. The role of cytotoxic antibodies in the equine pregnancy is not understood. The fact that they are not harmful to the pregnancy can be explained by the fact that their target, the paternal MHC molecules, are withdrawn from the endometrial cup tissue by the time the antibodies start appearing in the circulation. This unique way of regulation of MHC expression is also poorly understood.(ABSTRACT TRUNCATED AT 250 WORDS)     

Caged RNA: photo-control of a ribozyme reaction

We report here the first photo-chemical control of a ribozyme reaction by the site-specific modification of the 2'-hydroxyl nucleophile in the hammerhead system with a caging functionality. Rapid laser photolysis of the O-(2-nitrobenzyl) caging group initiates an efficient and accurate hammerhead-catalyzed cleavage of substrate RNA under native conditions. RNAs in which reactive functionalities or recognition elements are caged in this manner will be useful tools to probe RNA reactivity and dynamics.