Enzymatic transglycosylation of ginsenoside Rg1 by rice seed α-glucosidase

Six α-monoglucosyl derivatives of ginsenoside Rg1 (G-Rg1) were synthesized by transglycosylation reaction of rice seed α-glucosidase in the reaction mixture containing maltose as a glucosyl donor and G-Rg1 as an acceptor. Their chemical structures were identified by spectroscopic analysis, and the effects of reaction time, pH, and glycosyl donors on transglycosylation reaction were investigated. The results showed that rice seed α-glucosidase transfers α-glucosyl group from maltose to G-Rg1 by forming either α-1,3 (α-nigerosyl)-, α-1,4 (α-maltosyl)-, or α-1,6 (α-isomaltosyl)-glucosidic linkages in β-glucose moieties linked at the C6- and C20-position of protopanaxatriol (PPT)-type aglycone. The optimum pH range for the transglycosylation reaction was between 5.0 and 6.0. Rice seed α-glucosidase acted on maltose, soluble starch, and PNP α-D-glucopyranoside as glycosyl donors, but not on glucose, sucrose, or trehalose. These α-monoglucosyl derivatives of G-Rg1 were easily hydrolyzed to G-Rg1 by rat small intestinal and liver α-glucosidase in vitro.     

Effect of the chelation of metal cation on the antioxidant activity of chondroitin sulfates

The antioxidant potencies of chondroitin sulfates (CSs) from shark cartilage, salmon cartilage, bovine trachea, and porcine intestinal mucosa were compared by three representative methods for the measurement of the antioxidant activity; DPPH radical scavenging activity, superoxide radical scavenging activity, and hydroxyl radical scavenging activity. CSs from salmon cartilage and bovine trachea showed higher potency in comparison with CSs from shark cartilage and porcine intestinal mucosa. Next, CS from salmon cartilage chelating with Ca²⁺, Mg²⁺, Mn²⁺, or Zn²⁺ were prepared, and their antioxidant potencies were compared. CS chelating with Ca²⁺ or Mg²⁺ ions showed rather decreased DPPH radical scavenging activity in comparison with CS of H⁺ form. In contrast, CS chelating with Ca²⁺ or Mg²⁺ ion showed remarkably enhanced superoxide radical scavenging activity than CS of H⁺ or Na⁺ form. Moreover, CS chelating with divalent metal ions, Ca²⁺, Mg²⁺, Mn²⁺, or Zn²⁺, showed noticeably higher hydroxyl radical scavenging activity than CS of H⁺ or Na⁺ form. The present results revealed that the scavenging activities of, at least, superoxide radical and hydroxyl radical were enhanced by the chelation with divalent metal ions.     

Vitamin B12 deficiency-induced increase of osteoclastic bone resorption caused by abnormal renal resorption of inorganic phosphorus via Napi2a

Vitamin B₁₂ deficiency is a risk factor for bone disorders via mechanisms not fully understood. In this study, an increase in serum inorganic phosphorus (Pi) concentrations was associated with a vitamin B₁₂ deficiency. Napi2a, a renal cotransporter for Pi reabsorption, accumulated on plasma membranes in a vitamin B₁₂ deficiency suggests that vitamin B₁₂ plays an important role in Pi homeostasis.     

A short-term zinc-deficient diet decreases bone formation through down-regulated BMP2 in rat bone

We investigated the effects of a short-term dietary zinc deficiency on bone metabolism. Zinc deficiency increased the mRNA expression of zinc uptake transporters such as Zip1, Zip13, and Zip14 in bone. However, zinc deficiency might not maintain zinc storage in bone, resulting in a decrease in bone formation through downregulation of the expression levels of osteoblastogenesis-related genes.     

Characterization of NADP+-dependent isocitrate dehydrogenase isozymes from a psychrophilic bacterium,Colwellia psychrerythraea strain 34H

NADP⁺-dependent isocitrate dehydrogenase (IDH) isozymes of a psychrophilic bacterium, Colwellia psychrerythraea strain 34H, were characterized. The coexistence of monomeric and homodimeric IDHs in this bacterium was confirmed by Western blot analysis, the genes encoding two monomeric (IDH-IIa and IDH-IIb) and one dimeric (IDH-I) IDHs were cloned and overexpressed in Escherichia coli, and the three IDH proteins were purified. Both of the purified IDH-IIa and IDH-IIb were found to be cold-adapted enzymes while the purified IDH-I showed mesophilic properties. However, the specific activities of IDH-IIa and IDH-IIb were lower even at low temperatures than that of IDH-I. Therefore, IDH-I was suggested to be important for the growth of this bacterium. The results of colony formation of E. coli transformants carrying the respective IDH genes and IDH activities in their crude extracts indicated that the expression of the IDH-IIa gene is cold-inducible in the E. coli cells.     

Combined brain‐derived neurotrophic factor with extinction training alleviate impaired fear extinction in an animal model of post‐traumatic stress disorder

Impaired fear memory extinction (Ext) is one of the hallmark symptoms of post‐traumatic stress disorder (PTSD). However, since the precise mechanism of impaired Ext remains unknown, effective interventions have not yet been established. Recently, hippocampal‐prefrontal brain‐derived neurotrophic factor (BDNF) activity was shown to be crucial for Ext in naïve rats. We therefore examined whether decreased hippocampal‐prefrontal BDNF activity is also involved in the Ext of rats subjected to a single prolonged stress (SPS) as a model of PTSD. BDNF levels were measured by enzyme‐linked immunosorbent assay (ELISA), and phosphorylation of TrkB was measured by immunohistochemistry in the hippocampus and medial prefrontal cortex (mPFC) of SPS rats. We also examined whether BDNF infusion into the ventral mPFC or hippocampus alleviated the impaired Ext of SPS rats in the contextual fear conditioning paradigm. SPS significantly decreased the levels of BDNF in both the hippocampus and mPFC and TrkB phosphorylation in the ventral mPFC. Infusion of BDNF 24 hours after conditioning in the infralimbic cortex (ILC), but not the prelimbic cortex (PLC) nor hippocampus, alleviated the impairment of Ext. Since amelioration of impaired Ext by BDNF infusion did not occur without extinction training, it seems the two interventions must occur consecutively to alleviate impaired Ext. Additionally, BDNF infusion markedly increased TrkB phosphorylation in the ILC of SPS rats. These findings suggest that decreased BDNF signal transduction might be involved in the impaired Ext of SPS rats, and that activation of the BDNF‐TrkB signal might be a novel therapeutic strategy for the impaired Ext by stress.     

Isolation and characterization of a novel mycovirus infecting an edible mushroom,Grifola frondosa

Grifola frondosa (Maitake mushroom) is an important cultivated mushroom due to its medicinal and nutrient values. In this study, we isolated and characterized a novel partitivirus (named Grifola frondosa partitivirus 1, GfPV1) infecting a standard G. frondosa strain Gf-N2. This virus has a two-segmented dsRNA genome (dsRNA1 and dsRNA2) with nucleotide lengths of 2.3 and 2.2 kbp, respectively. The coding strand of dsRNA1 and dsRNA2 segments carries single open reading frame encoding RNA-dependent RNA polymerase (RdRp) and a coat protein (CP), respectively. BLAST searches and phylogenetic analyses showed that GfPV1 is most closely related to a betapartitivirus, Lentinula edodes partitivirus 1 (RdRp <70% and CP <60% amino acid sequence identities), but the sequence divergence suggests that GfPV1 is classifiable as a new member of the genus Betapartitivirus, family Partitiviridae. The presence of GfPV1 does not affect colony morphology and fruiting body development of G. frondosa. This is the first report investigating the effects of a mycovirus infection on the colony morphology and fruiting body development of G. frondosa. Interestingly, GfPV1 accumulations markedly decreased along with the fruiting body maturation stages, suggesting the inhibition of virus multiplication during sexual phase of the G. frondosa life cycle.     

Habitat generalization of a predatory ladybird,Harmonia yedoensis (Coleoptera: Coccinellidae), in an allopatric area with respect to its sibling species Harmonia axyridis

In central Japan, Harmonia yedoensis is a specialist ladybird that is confined to pine tree habitats, whereas its sibling species Harmonia axyridis is a generalist that feeds on a wide range of aphid species in nature. Interestingly, H. axyridis is not distributed in the Ryukyu Archipelago, southern Japan. We hypothesized that the ecological niche of H. yedoensis should be wider in the Ryukyu Archipelago, where its competitor species in central Japan, H. axyridis, is absent. We undertook fieldwork and a survey of published works to examine habitat utilization by H. yedoensis in the Ryukyu Archipelago. We found that H. yedoensis adults in the Ryukyu Archipelago visited several kinds of deciduous trees, including wild tamarind, Chinese hibiscus, Taiwan cherry and Malayan banyan, as well as pine trees. These observations suggest that habitat generalization has occurred in H. yedoensis in the Ryukyu Archipelago, where it does not compete with H. axyridis.