Efficacy of lasers as an adjunct to chemo-mechanical disinfection of infected root canals: a systematic review.

The aim was to evaluate the efficacy of various types of lasers used as an adjunct to chemo-mechanical disinfection of infected root canals with the outcome measures 'normal periapical condition' or 'reduction of microbial load'. PubMed, CENTRAL and ISI Web of Knowledge literature searches with specific indexing terms and a subsequent hand search were made with stated limits and criteria. Relevant publications were retrieved, followed by interpretation. The quality of each included publication was assessed as high, moderate or low. The initial search process yielded 234 publications. All abstracts of these publications were read, and the reference lists of relevant publications were hand-searched. Ten articles were read in full text and interpreted according to a data extraction form. Five were included in the systematic review and were assessed. A meta-analysis was impossible to perform because the included studies were heterogeneous with regard to study design, treatment and outcome measures. Positive effects were reported; however, no concluding evidence grade could be made because each included study was judged to have low quality, primarily due to lack of a power analysis, blinding and reproducibility. The evidence grade for whether lasers can be recommended as an adjunct to chemo-mechanical disinfection of infected root canals was insufficient. This does not necessarily imply that laser should not be used as an adjunct to root canal treatment but instead underscores the need for future high-quality studies.

Structural basis for allosteric substrate specificity regulation in anaerobic ribonucleotide reductases.

BACKGROUND: The specificity of ribonucleotide reductases (RNRs) toward their four substrates is governed by the binding of deoxyribonucleoside triphosphates (dNTPs) to the allosteric specificity site. Similar patterns in the kinetics of allosteric regulation have been a strong argument for a common evolutionary origin of the three otherwise widely divergent RNR classes. Recent structural information settled the case for divergent evolution; however, the structural basis for transmission of the allosteric signal is currently poorly understood. A comparative study of the conformational effects of the binding of different effectors has not yet been possible; in addition, only one RNR class has been studied. RESULTS: Our presentation of the structures of a class III anaerobic RNR in complex with four dNTPs allows a full comparison of the protein conformations. Discrimination among the effectors is achieved by two side chains, Gln-114 and Glu-181, from separate monomers. Large conformational changes in the active site (loop 2), in particular Phe-194, are induced by effector binding. The conformational differences observed in the protein when the purine effectors are compared with the pyrimidine effectors are large, while the differences observed within the purine group itself are more subtle. CONCLUSIONS: The subtle differences in base size and hydrogen bonding pattern at the effector site are communicated to major conformational changes in the active site. We propose that the altered overlap of Phe-194 with the substrate base governs hydrogen bonding patterns with main and side chain hydrogen bonding groups in the active site. The relevance for evolution is discussed.

Enzymatic catalysis in microemulsions: enzyme reuse and product recovery.

A technique for enzyme reuse and product recovery from enzymatic catalysis in microemulsions is demonstrated. The enzymatic reaction is performed in a homogeneous isotropic microemulsion; AOT (sodium bis-(2-ethyl- hexyl)sulfosuccinate)/isooctane/buffer or C(12)E(5)(penta ethylene glycol dodecyl ether)/heptane/buffer. By small temperature changes the systems are shifted to two phase regions, where an oil-rich phase, containing the product, coexists with a water-rich phase containing surfactant and enzyme. The oil-rich phase may be replaced by an oil solution containing new substrate. Thus, the reaction may be continued and the enzyme reused. This procedure was repeated nine times in the present study. Data on phase behavior in presence and in absence of protein, partitioning of the components and a radioactive-labelled protein between the phases, and the repeated use of horse liver alcohol dehydrogenase (HLADH) in the microemulsions are presented.

Analysis of the inactivation of liver alcohol dehydrogenase during storage in Aerosol-OT/isooctane microemulsions.

Changes in the enzymatic properties of horse liver alcohol dehydrogenase (HLADH; EC 1.1.1.1) were studied as a function of incubation time in Aerosol-OT/isooctane microemulsions. The enzyme was characterized by fluorimetric binding studies of the inhibitor isobutyramide to the binary complex, HLADH-NADH and by determination of Km,app and Vmax,app values for cyclohexanone. The Km,app values for cyclohexanone and the Kd,app for isobutyramide stay constant throughout a 48-h incubation, whereas the Vmax,app and the total number of inhibitor binding sites decrease. Thus the inactivation process previously described corresponds to progressive loss of functional sites, while the properties of the remaining functional sites are unchanged. If no co-enzyme is added to the system, the enzyme loses catalytic activity within less than an hour, but if co-enzyme is added, a fraction of the HLADH enzyme population retains enzyme activity over a long period of time. Hence the presence of bound co-enzyme significantly inhibits the process(es) leading to inactivation of the enzyme in the microemulsions.

Activity and stability of horse-liver alcohol dehydrogenase in sodium dioctylsulfosuccinate/cyclohexane reverse micelles.

Horse liver alcohol dehydrogenase (EC 1.1.1.1) solubilized in sodium dioctylsulfosuccinate (AOT)/cyclohexane reverse micelles was used for the oxidation of ethanol and reduction of cyclohexanone in a coupled substrate/coenzyme recycling system. The activity of the enzyme was studied as a function of pH and water content. The enzyme was optimally active in microemulsions prepared with buffer of pH around 8. An increase in enzymatic activity was observed as a function of increasing water content. The Km values for the substrates were calculated based on the total reaction volume. The apparent Km for ethanol in reverse micelles was about eight times lower as compared to that in buffer solution, whereas the Km for cyclohexanone was almost unaltered. Storage and operational stability were investigated. It was found that the specific activity of the alcohol dehydrogenase operating in reverse micellar solution was good for at least two weeks. The steroid eticholan-3 beta-ol-17-one was also used as a substrate. In this case the reaction rate was approximately five times higher in a reverse micellar solution than in buffer.