The functional characteristics of the forward and reverse transport modes of the human Na+/glucose transporter (hSGLT1) were investigated using plasma membrane vesicles of E. coli expressing the recombinant transporter. Correctly and inverse-oriented vesicles were employed to measure the initial rates of methyl-α-d-glucose uptake, under zero-trans conditions, as a function of Na+, sugar, and phlorizin concentrations and membrane potential. This approach enabled the analysis of the two faces of hSGLT1 in parallel, revealing the reversibility of Na+/sugar cotransport. While the key characteristics of secondary active sugar transport were maintained in both modes, namely, Na+ and voltage dependence, the kinetic properties of the two sides indicated a functional asymmetry of the transporter. That is, the apparent affinity for sugar and driver cation Na+ exhibited a difference of more than 1 order of magnitude between the two modes. Furthermore, the selectivity pattern of ligands and the interaction of the transporter with the competitive inhibitor phlorizin were different. Whereas the high-affinity substrates, d-glucose and d-galactose, inhibited uptake of radioactive sugar tracer at their physiological concentrations (10 mM) in the forward reaction, they were poor inhibitors even at high concentrations in the reverse transport mode. Taken together, these results confirm the successful employment of E. coli to express and characterize a human membrane protein (hSGLT1), elucidating the functional asymmetry of this cotransporter.

Background: Randomization allows study groups to be formed so that they are similar in all characteristics except outcomes. Aim: The aim of this study is to examine the frequency of randomization methods and their effect on achieving baseline balance in cluster randomization studies conducted in schools. Methods: A literature search of MEDLINE bibliographic database shows that the total number of collected articles in full text was 343, out of which 81 were eligible for inclusion. Each publication was reviewed by two independent reviewers, and data was extracted and analyzed. Results: Stratification was the most commonly applied randomization method, reported in 28 trials (34.6 %). There was no statistically significant difference in the number of subjects and clusters, as well as in cluster size between trial?s groups in studies in which simple randomization was used. However, there was a statistically significant difference in number of subjects and clusters between groups in trials in which restricted randomization methods were used. Yet, there was no difference in the cluster size. Conclusion: Although there is no difference in the size of clusters between trial arms, either at the level of the entire sample or in relation to randomization methods applied, additional research should be conducted on larger sample in order to establish the effect of randomization methods on baseline balance, when the size of clusters is in question.

The statistical dependence of protein secondary structure on amino acid bigram frequencies was studied. Proteins in the PDBSELECT subset of the Protein Data Bank database were investigated. Protein secondary structures were determined using DSSP software. The conditional probabilities of protein secondary structures were calculated and presented. The results on bigrams show the frequencies of all the possible bigrams in all secondary structure types. These results elucidate some factors important for the prediction of the secondary structures of proteins based on the amino acid sequence.