Administration timing and duration-dependent effects of sesamin isomers on lipid metabolism in rats.

Metabolism of lipids such as cholesterol and triglycerides has daily variations and is controlled by a circadian clock. Sesamin isomers, a mixture of sesamin and episesamin (SE), are types of lignans in sesame seed that have shown the improvement of lipid metabolism with various diseases in an animal model. We therefore tested whether the effects of SE on lipid metabolism are influenced by timing of administration. High-fat diet (HFD)-loaded rat was administered SE in the ZT13 or 14 (at the beginning of the active phase) or ZT23 or 22 (at the end of the active phase) every day for 7 or 28 days, and the effects on lipid metabolism were evaluated. The effects of SE were enhanced by duration-dependency: 28-day administration of SE strongly affected some parameters related to lipid metabolism, particularly cholesterol metabolism, as compared to 7-day administration. In particular, in 28-day administration, the analysis of serum and liver cholesterol levels revealed that SE administration decreases more effectively at the beginning of the active phase when compared to at the end of that. Furthermore, quantitative real-time polymerase chain reaction (QRT-PCR) and functional analysis indicated that suppression of cholesterol synthesis in the liver and promotion of cholesterol excretion from the liver, as well as inhibition of the functional activity and gene expression of sterol response element-binding protein 2 (Srebp2), which is a transcriptional factor and controls the gene expression involved in cholesterol-metabolism enzymes, contribute to enhancement of SE's effects at this administration timing. No significant differences were observed in triglyceride metabolism with regard to timing of SE administration. After 28-day administration of SE, administration at the beginning of the active phase only affected the expression of clock genes in the liver with phase-advance. In the pharmacokinetic study, administration time had no effect on the level of sesamin, episesamin or their metabolites in the liver after administration of SE for 28 days. The present results suggest that continuous long administration of SE at the beginning of the active phase is preferable for obtaining beneficial effects on lipid metabolism.

Identification and reconstitution of the rubber biosynthetic machinery on rubber particles from Hevea brasiliensis.

Natural rubber (NR) is stored in latex as rubber particles (RPs), rubber molecules surrounded by a lipid monolayer. Rubber transferase (RTase), the enzyme responsible for NR biosynthesis, is believed to be a member of the cis-prenyltransferase (cPT) family. However, none of the recombinant cPTs have shown RTase activity independently. We show that HRT1, a cPT from Heveabrasiliensis, exhibits distinct RTase activity in vitro only when it is introduced on detergent-washed HeveaRPs (WRPs) by a cell-free translation-coupled system. Using this system, a heterologous cPT from Lactucasativa also exhibited RTase activity, indicating proper introduction of cPT on RP is the key to reconstitute active RTase. RP proteomics and interaction network analyses revealed the formation of the protein complex consisting of HRT1, rubber elongation factor (REF) and HRT1-REF BRIDGING PROTEIN. The RTase activity enhancement observed for the complex assembled on WRPs indicates the HRT1-containing complex functions as the NR biosynthetic machinery.

Identification of a Highly Specific Isoflavone 7-O-glucosyltransferase in the soybean (Glycine max (L.) Merr.).

Isoflavone conjugates [7-O-ß-D-glucosides and 7-O-(6″-malonyl-ß-D-glucosides) of daidzein and genistein] accumulate in soybean roots and serve as the stored precursors of isoflavones (aglycons), which play very important roles in the rhizobia-mediated nodulation of this plant. Thus far, the isoflavone 7-O-glucosyltransferase (GmIF7GT or GmUGT1) has been biochemically characterized and is believed to be involved in isoflavone conjugate biosynthesis. The soybean genome encodes many other glycosyltransferase homologs (GmUGTs) that are related to GmUGT1; however, their catalytic properties, substrate specificities, and role(s) in isoflavone conjugation are unknown. In this study, nine different GmUGT1-related GmUGT cDNAs were isolated; six of these cDNAs belonged to two distinct phylogenetic subgroups (A and B), and these six were functionally characterized. The results showed that GmUGT4, a representative of subgroup A, encoded a UGT that was highly specific for isoflavones showing kcat and kcat/Km values for daidzein of 5.89 ± 0.65 s(-1) and 2.91 × 10(5) s(-1)M(-1), respectively. Moreover, GmUGT4 was expressed in the roots (mainly in lateral roots) of the 7-day-old seedlings and seeds, both of which contained abundant amounts of isoflavone conjugates. By contrast, GmUGT1 and GmUGT7, which were subgroup B members, encoded enzymes with broad glucosyl-acceptor specificities and were mainly expressed in the aerial portions (cotyledons and hypocotyls) of the seedlings. In the present study, we proposed that the role of isoflavone glucosylation in a soybean plant is assigned to different GmUGT members in an organ/tissue-dependent manner. We also established the functional importance of GmUGT4 in the biosynthesis of isoflavone conjugates in lateral roots that make a major contribution to overall N2 fixation.