Folded Structures in Protonated Reduced Dipeptides

Reduced dipeptides with the general formula RCO-Xaa- rXbb-N⁺HR′R′′ (rXbb, reduced analogue of residue Xbb: NH-C^α HR¹ -C_r H₂) are shown to adopt a folded conformation in solution and in the solid state. The protonated reduced amide bond is an active proton donor capable of interacting with a peptide carbonyl to give a strong hydrogen bond topologically equivalent to the i+2 or i+3? i interaction. The resulting conformation is similar to the γ- or β-turn structure found in peptides and proteins.     

The Influence of Genotype and Environment on the Physiological and Metabolic Diversity ofFusarium compactum

Talbot, N. J., Vincent, P., and Wildman, H. G. 1996. The influence of genotype and environment on the physiological and metabolic diversity ofFusarium compactum. Fungal Genetics and Biology20,254–267. Fungal species produce a large variety of secondary metabolites which are of considerable interest to the pharmaceutical industry. It is clear that the secondary metabolite production of a species varies significantly in strains from different geographic locations and from different habitats. The influence of genotype and environment on metabolite production is, however, poorly understood. In this study we examined the influence of genotypic variability, physiological variability, environmental location, and habitat on metabolite production byFusarium compactum.Isolates of the fungus from two geographic locations and two distinct habitat types were examined for growth on 95 different carbon sources, and genotypic variability was determined using RAPDs and rDNA–RFLP analysis. In a blind test secondary metabolite production was assessed using HPLC profiles of methanolic cell extracts. A number of correlations were observed between genotypic groupings, as determined using parsimony, and specific metabolite production. Similar correlations were also observed with physiological groups although genotypic analysis proved to be a more sensitive predictor of metabolite variability. The data suggest a complex relationship between environment, genotype, and metabolite production but highlight the use of genetic screening as a means of optimizing the chances of identifying a wide range of metabolites from a given species.     

Imprecise exposure assessment and the sample size requirements of case-control studies of residential magnetic field exposure and cancer in adults

A computer program simulating case-control studies is described. It is used to estimate the minimum sample size required and to assess how this is affected by imprecise exposure assessment. In particular, the consequences of neglecting measurements of nonresidential exposure in case-control studies of residentially exposed adults are investigated. According to this model, while the consequent loss of power is not as large as was predicted by algebraic methods, it would be unwise to neglect it when planning a study. © 1995 Wiley-Liss, Inc.     

Photophysics of the fluorescent K+ indicator PBFI.

The fluorescent indicator PBFI is widely used for the determination of intracellular concentrations of K+. To investigate the binding reaction of K+ to PBFI in the ground and excited states, steady-state and time-resolved measurements were performed. The fluorescence decay surface was analyzed with global compartmental analysis yielding the following values for the rate constants at room temperature in aqueous solution at pH 7.2: k01 = 1.1 x 10(9) s-1, k21 = 2.7 x 10(8) M-1s-1, k02 = 1.8 x 10(9) s-1, and k12 = 1.4 x 10(9) s-1. k01 and k02 denote the respective deactivation rate constants of the K+ free and bound forms of PBFI in the excited state. k21 represents the second-order rate constant of binding of K+ to the indicator in the excited state whereas k12 is the first-order rate constant of dissociation of the excited K(+)-PBFI complex. From the estimated values of k12 and k21, the dissociation constant Kd* in the excited state was calculated. It was found that pKd* (-0.7) is smaller than pKd (2.2). The effect of the excited-state reaction can be neglected in the determination of Kd and/or the K+ concentration. Therefore, intracellular K+ concentrations can be accurately determined from fluorimetric measurements by using PBFI as K+ indicator.     

Chromosome 17 abnormalities and lack of TP53 mutations in paediatric central nervous system tumours

Central nervous system (CNS) tumours are the most common solid tumours in children. Cytogenetic and molecular genetic studies of these neoplasms have previously shown abnormalities of chromosome 17, implicating genes on this autosome in tumorigenesis. To identify mutations in the TP53 tumour suppressor gene (17p13.1), we have sequenced the five highly conserved regions of this gene in 29 mixed paediatric CNS tumors. No mutations were detected by this analysis. In order to identify other candidate disease loci on chromosome 17, we have carried out a detailed deletion mapping analysis using 16 polymorphic DNA markers on 19 of the above tumours and an additional four cases. Abnormalities of chromosome 17 occurred in nine cases (39%), six of which were primitive neuroectodermal tumour (PNET)-medulloblastomas. These findings suggest that it is unlikely that the TP53 gene is directly involved in the development of common paediatric brain tumours. This is in contrast to findings from adult brain and other tumour types. Moreover, the frequency of chromosome 17 aberrations, especially in PNET-medulloblastomas, suggests that other genes on this chromosome contribute to tumourigenesis.     

Purification and characterization of the catabolic α-acetolactate synthase from Leuconostoc mesenteroides subsp. cremoris

The -acetolactate synthase from Leuconostoc mesenteroides subsp. cremoris was purified to homogeneity in SDS-PAGE. The enzyme is a trimer of 3×55,000 Da. It was unstable but could be preserved by addition of pyruvate and thiamine pyrophosphate in the buffer. The enzyme exhibits Michaelis-Menten kinetics, and K _m for pyruvate is 10 mM. Three intermediates in glucose metabolism (ATP, 3-phosphoglycerate, and phosphoenolpyruvate) exhibit a noncompetitive inhibition towards the enzyme. This enzyme does not require any divalent metal ion for activity. The -acetolactate synthase from Leuconostoc mesenteroides subsp. cremoris is not inhibited by the branched-chain amino acids (valine, leucine, and isoleucine), is FAD independent, and displays an optimal activity at pH 5.3. Therefore, it can be concluded that the purified enzyme belongs to the catabolic -acetolactate synthases, involved in the 2,3-butanediol pathway but not in branchedchain amino acids biosynthesis.     

Reproductive ecology of five pipefish species in one eelgrass meadow

Synopsis Synopsis Pipefishes have rarely been watched in the wild and have never before been followed in their common seagrass habitats. This study explores the reproductive ecology of five species of pipefishes living in a Swedish eelgrass meadow during parts of four breeding seasons, tagging four of the species. Pipefish are remarkable for their specialised paternal care: only males aerate, osmoregulate and nourish the developing embryos. Two of the species (Entelurus aequoreus andNerophis ophidion) have simple ventral gluing of eggs on the trunk while three species (Syngnathus acus, S. rostellatus andS. typhle) have fully enclosed brood pouches on their tails. Males of the former species receive eggs from one female while males of the genusSyngnathus receive partial clutches from several females. Sex ratios of adults on the site differed from equal to male-biased to female-biased, according to species.S. typhle were most numerous and were resighted most often. They were present throughout the breeding season whereas there were temporal shifts in the presence of the other species on the meadow and in some sex ratios. Most species occurred in the deeper, denser part of the meadow but there was some habitat separation by species and sex. All species tended to stay low in the eelgrass, primarily coming up above the eelgrass to display and mate. No species showed site fidelity either to a home range or to the meadow, withE. aequoreus adults spending least time on the meadow. Sexual size dimorphism differed: males were larger inS. rostellatus, the same size inS acus and smaller in the other species. Although the species overlap in habitat requirements and breeding season, the only observed interspecific interactions were abortive courtships betweenSyngnathus species.