Polycyclic aromatic hydrocarbons in rice grain dried by different processes: evaluation of a quick, easy, cheap, effective, rugged and safe extraction method.

This study aims at developing a method for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in rice grain samples by combining the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method and determination by gas chromatography-mass spectrometry (GC-EI-MS). Quantification limits ranging from 1 to 5µgkg(-1) were obtained. Recoveries ranged from 70% to 106% for most of the 16 PAHs under analysis. The optimised methodology was applied to assess safety concerning the content of PAHs in white and parboiled rice samples, dried by gas and wood burning. Although benzo(a)pyrene, the marker used for evaluating the carcinogenic risk of PAHs in food, was not detected in the samples, naphthalene and phenanthrene were detected in all of them. Since cereals have been shown to be an important source of PAHs in the diet, methods that perform the evaluation of the quality of this food group become relevant.

Structural analysis of a set of proteins resulting from a bacterial genomics project.

The targets of the Structural GenomiX (SGX) bacterial genomics project were proteins conserved in multiple prokaryotic organisms with no obvious sequence homolog in the Protein Data Bank of known structures. The outcome of this work was 80 structures, covering 60 unique sequences and 49 different genes. Experimental phase determination from proteins incorporating Se-Met was carried out for 45 structures with most of the remainder solved by molecular replacement using members of the experimentally phased set as search models. An automated tool was developed to deposit these structures in the Protein Data Bank, along with the associated X-ray diffraction data (including refined experimental phases) and experimentally confirmed sequences. BLAST comparisons of the SGX structures with structures that had appeared in the Protein Data Bank over the intervening 3.5 years since the SGX target list had been compiled identified homologs for 49 of the 60 unique sequences represented by the SGX structures. This result indicates that, for bacterial structures that are relatively easy to express, purify, and crystallize, the structural coverage of gene space is proceeding rapidly. More distant sequence-structure relationships between the SGX and PDB structures were investigated using PDB-BLAST and Combinatorial Extension (CE). Only one structure, SufD, has a truly unique topology compared to all folds in the PDB.

A structural genomics approach to the study of quorum sensing: crystal structures of three LuxS orthologs.

BACKGROUND: Quorum sensing is the mechanism by which bacteria control gene expression in response to cell density. Two major quorum-sensing systems have been identified, system 1 and system 2, each with a characteristic signaling molecule (autoinducer-1, or AI-1, in the case of system 1, and AI-2 in system 2). The luxS gene is required for the AI-2 system of quorum sensing. LuxS and AI-2 have been described in both Gram-negative and Gram-positive bacterial species and have been shown to be involved in the expression of virulence genes in several pathogens. RESULTS: The structure of the LuxS protein from three different bacterial species with resolutions ranging from 1.8 A to 2.4 A has been solved using an X-ray crystallographic structural genomics approach. The structure of LuxS reported here is seen to have a new alpha-beta fold. In all structures, an equivalent homodimer is observed. A metal ion identified as zinc was seen bound to a Cys-His-His triad. Methionine was found bound to the protein near the metal and at the dimer interface. CONCLUSIONS: These structures provide support for a hypothesis that explains the in vivo action of LuxS. Specifically, acting as a homodimer, the protein binds a methionine analog, S-ribosylhomocysteine (SRH). The zinc atom is in position to cleave the ribose ring in a step along the synthesis pathway of AI-2.

Melanocortin 3 receptor (MC3R) gene variants in extremely obese women.

OBJECTIVE: Following several reports of linkage of obesity related phenotypes to human chromosome 20q we sought to determine whether variations of the melanocortin 3 receptor (MC3R) gene are associated with obesity. DESIGN: We screened the MC3R gene coding region and approximately 2 kb of 5' and 3' flanking sequences for DNA variants in unrelated extremely obese women and average weight controls using polymerase chain reaction (PCR) single strand conformation polymorphism (SSCP) analysis and DNA sequencing. SUBJECTS: 124 unrelated extremely obese women (body mass index, (BMI)>/=40 kg/m2) and 85 average weight controls (BMI<27 kg/m2). MEASUREMENTS: Radiation hybrid (RH) mapping was performed to localize the MC3R gene. 5' and 3' flanking sequences of MC3R gene were cloned. PCR-SSCP and DNA sequencing were used to detect mutations in the MC3R gene coding region and flanking sequences. RESULTS: RH mapping localized the MC3R gene to 20q13, between markers D20S100 and D20S149. 1083 bp 5' and 653 bp 3' flanking region of the MC3R gene were cloned. A missense mutation (+241, codon 81 ATT/GTT, Ile-->Val) was found in the MC3R coding region. Four more variants were detected in the 5' flanking sequence: -201(C-->G), -239 (A-->G), -762(A-->T) and -769(T-->C). Compared with controls, no significant allele frequency differences were found. Racial differences were found for the +241, -201, -239 and -762 polymorphisms. CONCLUSIONS: Several sequence variants were found in the MC3R gene coding region and in 5' flanking sequences. However, none of the variants were associated with obesity phenotypes. The linkage of extreme human obesity on 20q13 is likely caused by genes other than MC3R. International Journal of Obesity (2000) 24, 206-210

Mycotoxins and fungi in wheat stored in elevators in the state of Rio Grande do Sul, Brazil.

Samples of wheat harvested from 1988 to 1990 and stored in elevators in the south of Brazil (12 Brazilian, 4 Argentinian and 2 Uruguayan) were analysed in 1990 for 14 mycotoxins: deoxynivalenol (DON), nivalenol, diacetoxyscirpenol (DAS), T-2 and HT-2 toxins, T-2 triol, T-2 tetraol, aflatoxins B1, B2, G1, G2, ochratoxin A (OCHRA A), zearalenone and sterigmatocystin. One sample (1988 harvest) was contaminated with OCHRA A (0.04 microgram/g) and three other samples (1990 harvest) were contaminated with DON (0.40 microgram/g), DAS (0.30 microgram/g), T-2 (two samples, 0.35 and 0.36 gamma g/g) and T-2 tetraol (1.68 micrograms/g). Fusarium graminearum Schwabe was found in the 1990 samples with a relative incidence ranging from 1 to 22% and predominated in Argentinian and Uruguayan wheat (1990 harvest). Fusarium dimerum Penzig (8-75%) was the main Fusarium sp. in Brazilian wheat from the 1990 harvest.

Mycotoxins and fungi in wheat harvested during 1990 in test plots in the state of São Paulo, Brazil.

Wheat from two cultivars with contrasting characteristics were harvested in ten experimental plots located in wheat producing areas of the State of São Paulo, Brazil. The samples (10 of each cultivar) were analyzed by a gas-chromatographic method for deoxynivalenol (DON), nivalenol (NIV), diacetoxyscirpenol (DAS), toxins T-2 (T-2) and HT-2, T-2 tetraol, T-2 triol, and by a thin-layer chromatographic method for zearalenone (ZEN), aflatoxins B1, B2, G1, G2, ochratoxin A and sterigmatocystin. No mycotoxins were detected in 13 samples. DON was found in four samples (0.47-0.59 microgram/g), NIV in three samples (0.16-0.40 microgram/g), T-2 in two samples (0.40, 0.80 microgram/g), DAS in one sample (0.60 microgram/g), and ZEN in three samples (0.04-0.21 microgram/g). The wheat samples were also examined for the incidence of fungi. Alternaria, Drechslera, Epicoccum and Cladosporium were the prevailing genera. Among the Fusarium spp., F. semitectum was present in 19 samples and F. moniliforme in 18 samples. No F. graminearum was isolated in the samples.