Mitochondrial recycling of ascorbic acid as a mechanism for regenerating cellular ascorbate

Mitochondria are the major source of potentially damaging reactive oxygen species in most cells. Since ascorbic acid, or vitamin C, can protect against cellular oxidant stress, we studied the ability of mitochondria prepared from guinea pig skeletal muscle to recycle the vitamin from its oxidized forms. Although ascorbate concentrations in freshly prepared mitochondria were only about 0.2 mM, when provided with 6 mM succinate and 1 mM dehydroascorbate (the two-electron-oxidized form of the vitamin), mitochondria were able to generate and maintain concentrations as high as 4 mM, while releasing most of the ascorbate into the incubation medium. Mitochondrial reduction of dehydroascorbate was strongly inhibited by 1,3-bis(chloroethyl)-1-nitrosourea and by phenylarsine oxide. Despite existing evidence that mitochondrial ascorbate protects the organelle from oxidant damage, ascorbate failed to preserve mitochondrial alpha-tocopherol during prolonged incubation in oxygenated buffer. Nonetheless, the capacity for mitochondria to recycle ascorbate from its oxidized forms, measured as ascorbate-dependent ferricyanide reduction, was several-fold greater than total steady-state ascorbate concentrations. This, and the finding that more than half of the ascorbate recycled from dehydroascorbate escaped the mitochondrion, suggests that mitochondrial recycling of ascorbate might be an important mechanism for regenerating intracellular ascorbate.     

Aluminium resistance requires resistance to acid stress: a case study with spinach that exudes oxalate rapidly when exposed to Al stress

Spinach is a vegetable with a high oxalate concentration in its tissues. Oxalate efflux from spinach (Spinacia oleracea L. cv. Quanneng) roots was rapidly stimulated (within 30 min) by aluminium (Al) treatment. The efflux was constant within 6 h, but increased with increasing Al concentration. The efflux was confined to the root tip (0-5 mm), which showed a 5-fold greater efflux than the root zone distal to the tip (5-10 mm). Oxalate efflux could not be triggered by treatment with the trivalent cation lanthanum or by phosphorus deficiency, indicating that the efflux was specific to the Al treatment. All this evidence suggested that spinach possesses Al-resistance mechanisms. However, spinach was found to be as sensitive to Al toxicity as the Al-sensitive wheat line ES8, which had no Al-dependent organic acids efflux. The Al accumulated in the apical 5 mm of the roots of spinach which was also similar to that in the Al-sensitive wheat after 24 h treatment with 50 microM AlCl(3), indicating a non-exclusion mechanism. In addition, root elongation in spinach was significantly inhibited at pH 4.5, compared with that at pH 6.5. Based on this evidence, it is concluded that the sensitivity to acid stress in spinach could mask the potential role for oxalate to protect the plant roots from Al toxicity.     

Prevalence of Gestational Diabetes Mellitus and Its Risk Factors in Chinese Pregnant Women: A Prospective Population-Based Study in Tianjin,China

Objective

We compared the increases in the prevalence of gestational diabetes mellitus (GDM) based on the 1999 World Health Organization (WHO) criteria and its risk factors in Tianjin, China, over a 12-year period. We also examined the changes in the prevalence using the criteria of International Association of Diabetes and Pregnancy Study Group (IADPSG).

Methods

In 2010-2012, 18589 women who registered within 12 weeks of gestation underwent a glucose challenge test (GCT) at 24-28 gestational weeks. Amongst them, 2953 women with 1-hour plasma glucose ≥7.8 mmol/L underwent a 75-gram 2-hour oral glucose tolerance test (OGTT) and 781 women had a positive GCT but absented from the standard OGTT. An adjusted prevalence of GDM was calculated for the whole cohort of women by including an estimate of the proportion of women with positive GCTs who did not have OGTTs but would have been expected to have GDM. Logistic regression was used to obtain odds ratios and 95% confidence intervals using the IADPSG criteria. The prevalence of GDM risk factors was compared to the 1999 survey.

Results

The adjusted prevalence of GDM by the 1999 WHO criteria was 8.1%, a 3.5-fold increase as in 1999. Using the IADPSG criteria increased the adjusted prevalence further to 9.3%. Advanced age, higher pre-pregnancy body mass index, Han-nationality, higher systolic blood pressure (BP), a family history of diabetes, weight gain during pregnancy and habitual smoking were risk factors for GDM. Compared to the 1999 survey, the prevalence of overweight plus obesity had increased by 1.8 folds, age≥30 years by 2.3 folds, systolic BP by 2.3 mmHg over the 12-year period.

Conclusions

Increasing prevalence of overweight/obesity and older age at pregnancy were accompanied by increasing prevalence of GDM, further increased by change in diagnostic criteria.     

Isolation and characterization of 12 polymorphic microsatellite markers from ladyfish (Elops saurus Linnaeus)

Ladyfish (Elops saurus Linnaeus) is an economically important marine fish species. 76 microsatellite loci were isolated from an enriched genomic library of Elops saurus. Twelve of these markers were polymorphic in a test population with alleles per locus ranging from three to nine. The number of observed, expected heterozygosity and polymorphism information content (PIC) per locus in 20 individuals ranged from 0.2000 to 1.0000, 0.1897–0.8846, 0.1769–0.8476, respectively. One markers significantly deviated from Hardy-Weinberg equilibrium after Bonferroni correction analysis and there was no significant linkage disequilibrium found between pairs of markers. As a result, 12 microsatellite markers probably should provide sufficient level of genetic diversity to investigate the fine-scale population structure, stock management and enhancement, genetic linkage map construction and molecular marker-assisted breeding in Elops saurus Linnaeus.     

A shared epitope of the interphotoreceptor retinoid-binding protein recognized by the CD4+ and CD8+ autoreactive T cells

We previously demonstrated that cultures of rat uveitogenic T cells rapidly become dominated by CD4+ cells, but activation of CD8+ autoreactive T cells also occurred during the in vitro culture of in vivo-primed T cells. In the present study, we show that the commonly used uveitogenic peptide, interphotoreceptor retinoid-binding protein (IRBP) 1-20, generated both CD4+ and CD8+ autoreactive T cells in the C57BL/6 (B6) mouse and that this 20-mer contains at least two distinct antigenic epitopes. To determine whether the CD8 response was Ag-specific and whether CD4+ and CD8+ IRBP1-20-specific T cells recognize distinct antigenic epitopes, we prepared highly purified CD4+ and CD8+ T cells from IRBP1-20-primed mice and tested their proliferative response to a large panel of truncated peptides derived from IRBP1-20. The results showed that both CD4+ and CD8+ T cells recognized the same spectrum of peptides. In addition, peptides P10-18 were found to bind effectively to CD8+ IRBP1-20-specific T cells when complexed with recombinant H-2K(b) and also stimulate the proliferation and cytokine production of CD4+ IRBP1-20-specific T cells. Our results document for the first time that CD8+ and CD4+ autoreactive T cells display characteristic epitope recognition and they both recognize the same core epitope.     

Cryptic plasmid pSKU146 from the wall-less plant pathogen Spiroplasma kunkelii encodes an adhesin and components of a type IV translocation-related conjugation system

A cryptic plasmid of the wall-less plant pathogenic mollicute, Spiroplasma kunkelii CR2-3X, was cloned and its sequence analyzed. The 14,615 bp plasmid, designated pSKU146, has a nucleotide content of 28 mol% G + C, and contains 18 potential protein-coding regions (open reading frames, ORFs), of which six encode proteins that exhibit similarity to virulence-associated proteins involved in cell-to-cell adhesion or conjugal DNA transfer. One ORF encodes a 96 kDa protein, SkARP1, that is highly similar to SARP1 adhesin involved in attachment of Spiroplasma citri to insect vector gut membrane. Five ORFs encode proteins similar to TraE and Mob in walled bacteria, and to ORFs found in the integrative, conjugative element (ICEF) of Mycoplasma fermentans, respectively. Presence of domains similar to proteins of the Type IV secretion system in pathogenic bacteria suggests that spiroplasma possesses a related translocation system. Plasmid pSKU146 also contains two identical oriT regions each containing a nick sequence characteristic of the IncP conjugative plasmid family, as well as a 58 bp palindromic sequence, palSK1. Features in pSKU146 suggest that the plasmid functions as a mobile genetic element in conjugative transmission of spiroplasma pathogenicity-related genes.     

A comparative analysis of genetic diversity in medicinal Chrysanthemum morifolium based on morphology, ISSR and SRAP markers

The diversity and genetic relationship among 29 populations of Chrysanthemum morifolium, one of Chrysanthemum indicum and one of Chrysanthemum nankingense from China were analyzed using morphological traits and molecular markers. Twenty morphological traits were scored as well as 182 ISSR marker-fragments, as amplified by 22 primers [the percentage of polymorphic bands (PPB): 81.87%], and 243 SRAP marker-fragments as generated by 26 primer pairs (PPB: 75.72%). Mantel’s test indicated significant correlation (r = 0.624) of morphological trait and SRAP. By contrast, the morphological trait showed low correlation with ISSR (r = 0.246). Cluster analysis showed groupings of the accessions according to all four methods correlated well with their geographic region of origin, and most populations from the south of China were classified into one cluster and most populations from the north of China were classified into another cluster. Finally, an appropriate strategy for conserving the C. morifolium germplasm was proposed.     

黄嘌呤氧化还原酶的结构、功能和作用

黄嘌呤氧化还原酶(XOR)参与人体内的嘌呤代谢,并且是这一代谢过程的限速酶。其终产物是活性氧(包括OH·、H2O2和O2-)和尿酸。这两种产物参与体内多种生理活动。从XOR基因的结构、XOR蛋白的分子结构和基本功能、控制XOR活性的多个环节以及XOR的两种催化产物活性氧和尿酸在生理和病理情况下的功能及机制进行了总结,以期对XOR的发现、研究历史及现状和有待解决的问题有一个系统的了解。