基于RFC3576协议的E3RAS主动控制系统研究

简要介绍了RADIUS协议的基本概念,介绍了RFC3576协议的基本原理,阐述了如何基于RADIUS协议实现一套基于web的BRAS上网会话的主动控制系统。     

Isolation of an acetyl-CoA synthetase gene (ZbACS2) from Zygosaccharomyces bailii

A gene homologous to Saccharomyces cerevisiae ACS genes, coding for acetyl-CoA synthetase, has been cloned from the yeast Zygosaccharomyces bailii ISA 1307, by using reverse genetic approaches. A probe obtained by PCR amplification from Z. bailii DNA, using primers derived from two conserved regions of yeast ACS proteins, RIGAIHSVVF (ScAcs1p; 210-219) and RVDDVVNVSG (ScAcs1p; 574-583), was used for screening a Z. bailii genomic library. Nine clones with partially overlapping inserts were isolated. The sequenced DNA fragment contains a complete ORF of 2027 bp (ZbACS2) and the deduced polypeptide shares significant homologies with the products of ACS2 genes from S. cerevisiae and Kluyveromyces lactis (81% and 82% identity and 84% and 89% similarity, respectively). Phylogenetic analysis shows that the sequence of Zbacs2 is more closely related to the sequences from Acs2 than to those from Acs1 proteins. Moreover, this analysis revealed that the gene duplication producing Acs1 and Acs2 proteins has occurred in the common ancestor of S. cerevisiae, K. lactis, Candida albicans, C. glabrata and Debaryomyces hansenii lineages. Additionally, the cloned gene allowed growth of S. cerevisiae Scacs2 null mutant, in medium containing glucose as the only carbon and energy source, indicating that it encodes a functional acetyl-CoA synthetase. Also, S. cerevisiae cells expressing ZbACS2 have a shorter lag time, in medium containing glucose (2%, w/v) plus acetic acid (0.1-0.35%, v/v). No differences in cell response to acetic acid stress were detected both by specific growth and death rates. The mode of regulation of ZbACS2 appears to be different from ScACS2 and KlACS2, being subject to repression by a glucose pulse in acetic acid-grown cells.     

Inhibition of Human α‐Methylacyl CoA Racemase (AMACR): a Target for Prostate Cancer

The enzyme α‐methylacyl CoA racemase (AMACR) is involved in the metabolism of branched‐chain fatty acids and has been identified as a promising therapeutic target for prostate cancer. By using the recently available human AMACR from HEK293 kidney cell cultures, we tested a series of new rationally designed inhibitors to determine the structural requirements in the acyl component. An N‐methylthiocarbamate (K_i=98 nM ), designed to mimic the proposed enzyme‐bound enolate, was found to be the most potent AMACR inhibitor reported to date.     

Gut Microbial Fatty Acid Metabolites Reduce Triacylglycerol Levels in Hepatocytes

Hydroxy and oxo fatty acids were recently found to be produced as intermediates during gut microbial fatty acid metabolism. Lactobacillus plantarum produces these fatty acids from unsaturated fatty acids such as linoleic acid. In this study, we investigated the effects of these gut microbial fatty acid metabolites on the lipogenesis in liver cells. We screened their effect on sterol regulatory element binding protein‐1c (SREBP‐1c) expression in HepG2 cells treated with a synthetic liver X receptor α (LXRα) agonist (T0901317). The results showed that 10‐hydroxy‐12(Z)‐octadecenoic acid (18:1) (HYA), 10‐hydroxy‐6(Z),12(Z)‐octadecadienoic acid (18:2) (γHYA), 10‐oxo‐12(Z)‐18:1 (KetoA), and 10‐oxo‐6(Z),12(Z)‐18:2 (γKetoA) significantly decreased SREBP‐1c mRNA expression induced by T0901317. These fatty acids also downregulated the mRNA expression of lipogenic genes by suppressing LXRα activity and inhibiting SREBP‐1 maturation. Oral administration of KetoA, which effectively reduced triacylglycerol accumulation and acetyl‐CoA carboxylase 2 (ACC2) expression in HepG2 cells, for 2 weeks significantly decreased Srebp‐1c, Scd‐1, and Acc2 expression in the liver of mice fed a high‐sucrose diet. Our findings suggest that the hypolipidemic effect of the fatty acid metabolites produced by L. plantarum can be exploited in the treatment of cardiovascular diseases or dyslipidemia.     

Bovine Brain Region‐Specific Stearoyl‐CoA Desaturase Expression and Fatty Acid Composition

In this study, we sought to determine the relationship between stearoyl‐CoA desaturase (SCD) gene isoform expression in the bovine brain and the accumulation of 18:1n‐9. Two SCD gene isoforms are found in cows—SCD1 and SCD5. Samples of six brain regions (cerebellum, frontal cortex, hippocampus, hypothalamus, midbrain, and pons) were collected from animals at four different ages (neonates, weanlings, yearlings, and adults) for mRNA isolation and fatty acid analysis. Expression of SCD1 and SCD5 mRNA was compared across age groups to determine its developmental regulation. Fatty acid composition and SCD isoform mRNA expression were compared to examine the correlation of SCD1 and SCD5 with 18:1n‐9 content in different brain regions. We found statistically significant correlations between SCD1 and SCD5 mRNA expression and the ratio of 18:1n‐9 to 18:0 across age groups, with stronger correlations observed for SCD5. Similarly, there was a significant correlation between the ratio of 18:1n‐9 to 18:0 and SCD5 mRNA expression across brain regions. SCD1 mRNA and the 18:1n‐9 to 18:0 ratio were negatively correlated in the hippocampus. There was no trend of increasing 18:1n‐9 content or SCD expression with age. Correlations indicated a stronger relationship between SCD5 mRNA expression and the 18:1n‐9 to 18:0 ratio, potentially indicating a strong contribution of the SCD5 isoform to brain 18:1n‐9 content. This is the first study examining a potential role for SCD5 in providing 18:1n‐9 for brain lipids.     

Acetyl CoA carboxylase shares control of fatty acid synthesis with fatty acid synthase in bovine mammary homogenate

The objectives of this research were to determine the flux control coefficients for acetyl CoA carboxylase and fatty acid synthase using an in vitro preparation of bovine mammary homogenate. For an enzyme to be considered rate limiting with the use of metabolic control analysis, its control coefficient would be equal to unity. The hypothesis for this experiment was that the control coefficient for acetyl CoA carboxylase was not equal to unity, and that this enzyme was not, therefore, the rate-limiting step. Mammary tissue was isolated from lactating Holstein cows at slaughter and frozen in liquid nitrogen. Tissue was ground, homogenized, and centrifuged to obtain a postmitochondrial supernatant for use in in vitro incubations containing labeled acetate. Specific inhibitors for acetyl CoA carboxylase and fatty acid synthase were used to fractionally inhibit de novo synthesis for the calculation of flux control coefficients. The composition of fatty acids synthesized in the absence of enzyme inhibitors was similar to the composition of fatty acids in the presence of inhibitors. Calculations following avidin inhibition of acetyl CoA carboxylase determined the flux control coefficient was 0.63 ± 0.15, which means that 63% of the control of fatty acid synthesis is exerted by acetyl CoA carboxylase. The remaining control (37%) was from fatty acid synthase, which indicates a significant degree of control over the flux of acetate in de novo synthesis resides with this enzyme. The rate-limiting status ascribed to acetyl CoA carboxylase was not supported, because the flux control coefficient was less than unity. Metabolic control analysis, through its use of pathway product measurements, allows for potential interactions in the pathway such as feedback inhibition contribution to the flux control coefficients, which would not otherwise be considered in studies measuring enzyme kinetics with purified enzymes.     

Differential effects of obesity on acetoacetyl‐CoA synthetase gene in rat adipose tissues

In order to investigate the physiological role of the ketone body‐utilizing enzyme acetoacetyl‐CoA synthetase (AACS) in obesity‐induced metabolic derangements, we examined the mRNA levels of AACS and other lipogenic enzymes in white adipose tissues (WAT) in the different types of obesity, genetic (Zucker fatty) and high‐fat diet (HFD)‐induced obesity. Plasma ketone body levels and gene expression levels of AACS and acetyl‐CoA carboxylase‐2 (ACC‐2) in WAT were lower in Zucker fatty rats than in lean rats. On the contrary, in HFD‐induced obese rats, these levels were increased. Moreover, AACS mRNA expression was affected only in subcutaneous WAT by each type of obesity. Our data suggest that AACS mRNA expression is related to obesity‐induced alteration of plasma ketone body levels, and that AACS in subcutaneous WAT plays an important role in the regulation of lipogenesis and ketone body utilization in various obese conditions.