A Single Peroxisomal Targeting Signal Mediates Matrix Protein Import in Diatoms

Peroxisomes are single membrane bound compartments. They are thought to be present in almost all eukaryotic cells, although the bulk of our knowledge about peroxisomes has been generated from only a handful of model organisms. Peroxisomal matrix proteins are synthesized cytosolically and posttranslationally imported into the peroxisomal matrix. The import is generally thought to be mediated by two different targeting signals. These are respectively recognized by the two import receptor proteins Pex5 and Pex7, which facilitate transport across the peroxisomal membrane. Here, we show the first in vivo localization studies of peroxisomes in a representative organism of the ecologically relevant group of diatoms using fluorescence and transmission electron microscopy. By expression of various homologous and heterologous fusion proteins we demonstrate that targeting of Phaeodactylum tricornutum peroxisomal matrix proteins is mediated only by PTS1 targeting signals, also for proteins that are in other systems imported via a PTS2 mode of action. Additional in silico analyses suggest this surprising finding may also apply to further diatoms. Our data suggest that loss of the PTS2 peroxisomal import signal is not reserved to Caenorhabditis elegans as a single exception, but has also occurred in evolutionary divergent organisms. Obviously, targeting switching from PTS2 to PTS1 across different major eukaryotic groups might have occurred for different reasons. Thus, our findings question the widespread assumption that import of peroxisomal matrix proteins is generally mediated by two different targeting signals. Our results implicate that there apparently must have been an event causing the loss of one targeting signal even in the group of diatoms. Different possibilities are discussed that indicate multiple reasons for the detected targeting switching from PTS2 to PTS1

Comparison of methods for determining moisture content of citrus and eucalyptus Brazilian honeys by refractometry

The official method in Brazilian legislation for determining moisture content in honey is the one established by the Association of Official and Analytical Chemists (AOAC). Recently, the European Honey Commission (EHC) proposed a modification of this method suggesting a pre-treatment for crystallized honey samples. The objectives of the present work were: to study by factorial design the influence of pre-treatment and physical state of sample on moisture content determined by refractometry; to choose the better procedure and determine the average value of moisture content of 50 citrus and eucalyptus honey samples. Samples were collected in Sao Paulo State, Brazil during 1996-1998. An Abbe Refractometer thermostatted at 20 degreesC was used and the pre-treatment was done in a water bath at 50 degreesC until crystal dissolution. The effects of the variables of factorial design (pre-treatment and physical state) were significant at 95% level. Results of this design showed that the use of the pre-treatment, suggested by EHC, is superior for analysis of liquid and crystallized honey samples. The moisture values obtained for eucalyptus were higher than those for citrus honey samples independent of the analysis method used. (C) 2001 Academic Press.14110110

Characterization of monofloral honeys by ash contents through a hierarchical design

With increasing world interest in honey characterization various studies have been carried out relating physicochemical parameters to botanical and geographical origins. Ash content is one of these parameters that has been associated with floral sources of honey samples. However, little attention has been given to the determination of how much of the variability in ash contents is caused by contributions of different floral sources or honey samplings compared to the variations caused by analytical errors. So, in this work, a two stage hierarchical statistical design is employed to quantify the sizes of these different variational sources. An extremely significant effect on ash content owing to floral origin of Eucalyptus and Citrus honey samples was found. A smaller but significant variation was also observed for different samples from the same floral source. This sampling variance can be associated with different environmental and geographical conditions, different technological aspects of production and processing of honeys since the honey samples were obtained from various beekeepers and collected in diverse regions of Sao Paulo State, Brazil. Considering that the variation owing to floral source is much larger than the one observed for sampling and analysis errors, ash content could be used to characterize these two types of monofloral honeys. (C) 2003 Published by Elsevier Inc.17673774

Physicochemical characterization and antioxidant activity of 17 commercial Moroccan honeys

In this study, 17 commercial honey samples from Morocco were analyzed. Four samples did not meet the international physicochemical standards due to high hydroxymethylfurfural content and low diastase activity. Phenol content varied from 163.82mg gallic acid equivalent (GAE)/kg in citrus honey to 923.70mg (GAE)/kg in thyme honey from Rachidia; flavonoid content ranged from 4.26mg quercetin equivalent (QE)/kg in citrus honey to 139.62mg QE/kg in black cumin honey. Black cumin honey had the highest peroxyl scavenging activity; oregano (from Zaraphyt) and thyme honeys (from Rachidia) had the highest ABTS (2,2'-azino-bis[ 3-ethylbenzothiazoline-6-sulphonic acid]) scavenging activity; and thyme honey (Saouira) had the highest NO scavenging capacity. The antioxidant activity of Moroccan honeys was correlated with the phenol, flavonoid, and melanoidin contents. Dark honeys had higher antioxidant activity than light honeys. Samples with high sodium levels had lower free radical scavenging activity. On the other hand, calcium and magnesium increased the ABTS and peroxyl scavenging capacity, respectively, of honey samples. According to cluster and discriminant analyses, the honey samples were grouped in three clusters with respect to the phenol, flavonoid, melanoidin, proline, mineral and sugar contents, and free radical scavenging capacity