Impacts of elevated CO2 concentration on biochemical composition, carbonic anhydrase, and nitrate reductase activity of freshwater green algae

To investigate the biochemical response of freshwater green algae to elevated CO2 concentrations, Chlorella pyrenoidosa Chick and Chlamydomonas reinhardtii Dang cells were cultured at different CO2 concentrations within the range 3-186 μ mol/L and the biochemical composition, carbonic anhydrase (CA), and nitrate reductase activities of the cells were investigated. Chlorophylls (Chl), carotenoids, carbonhydrate, and protein contents were enhanced to varying extents with increasing CO2 concentration from 3-186 μ mol/L. The CO2 enrichment significantly increased the Chl a/Chl b ratio in Chlorella pyrenoidosa, but not in Chlamydomonas reinhardtii. The CO2 concentration had significant effects on CA and nitrate reductase activity. Elevating CO2 concentration to 186 μ mol/L caused a decline in intracellular and extracellullar CA activity. Nitrate reductase activity, under either light or dark conditions, in C. reinhardtii and C. pyrenoidosa was also significantly decreased with CO2 enrichment. From this study, it can be concluded that CO2 enrichment can affect biochemical composition, CA, and nitrate reductase activity, and that the biochemical response was species dependent.

Docking and molecular dynamics study on the inhibitory activity of coumarins on aldose reductase

In order to explore the inhibitory mechanism of coumarins toward aldose reductase (ALR2), AutoDock and Gromacs software were used for docking and molecular dynamics studies on 14 coumarins (CM) and ALR2 protease. The docking results indicate that residues TYR48, HIS110, and TRP111 construct the active pocket of ALR2 and, besides van der Waals and hydrophobic interaction, CM mainly interact with ALR2 by forming hydrogen bonds to cause inhibitory behavior. Except for CM1, all the other coumarins take the lactone part as acceptor to build up the hydrogen bond network with active-pocket residues. Unlike CM3, which has two comparable binding modes with ALR2, most coumarins only have one dominant orientation in their binding sites. The molecular dynamics calculation, based on the docking results, implies that the orientations of CM in the active pocket show different stabilities. Orientation of CM1 and CM3a take an unstable binding mode with ALR2; their conformations and RMSDs relative to ALR2 change a lot with the dynamic process. While the remaining CM are always hydrogen-bonded with residues TYR48 and HIS110 through the carbonyl O atom of the lactone group during the whole process, they retain the original binding mode and gradually reach dynamic equilibrium.

Docking and molecular dynamics studies toward the binding of new natural phenolic marine inhibitors and aldose reductase

Phenolic marine natural product is a kind of new potential aldose reductase inhibitors (ARIs). In order to investigate the binding mode and inhibition mechanism, molecular docking and dynamics studies were performed to explore the interactions of six phenolic inhibitors with human aldose reductase (hALR2). Considering physiological environment, all the neutral and other two ionized states of each phenolic inhibitor were adopted in the simulation. The calculations indicate that all the inhibitors are able to form stable hydrogen bonds with the hALR2 active pocket which is mainly constructed by residues TYR48, HIS110 and TRP111, and they impose the inhibition effect by occupying the active space. In all inhibitors, only La and its two ionized derivatives La_ion1 and La_ion2, in which neither of the ortho-hydrogens of 3-hydroxyl is substituted by Br, bind with hALR2 active residues using the terminal 3-hydroxyl. While, all the other inhibitors, at least one of whose ortho-sites of 3- and 6-hydroxyls are substituted by Br substituent which take much electron-withdrawing effect and steric hindrance, bind with hALR2 through the lactone group. This means that the Br substituent can effectively regulate the binding modes of phenolic inhibitors. Although the lactone bound inhibitors have relatively high RMSD values, our dynamics study shows that both binding modes are of high stability. For each inhibitor molecule, the ionization does not change its original binding mode, but it does gradually increase the binding free energy, which reveals that besides hydrogen bonds, the electrostatic effect is also important to the inhibitor–hALR2 interaction.

5-α reductase inhibitors and prostate cancer prevention: where do we turn now?

With the lifetime risk of being diagnosed with prostate cancer so great, an effective chemopreventive agent could have a profound impact on the lives of men. Despite decades of searching for such an agent, physicians still do not have an approved drug to offer their patients. In this article, we outline current strategies for preventing prostate cancer in general, with a focus on the 5-α-reductase inhibitors (5-ARIs) finasteride and dutasteride. We discuss the two landmark randomized, controlled trials of finasteride and dutasteride, highlighting the controversies stemming from the results, and address the issue of 5-ARI use, including reasons why providers may be hesitant to use these agents for chemoprevention. We further discuss the recent US Food and Drug Administration ruling against the proposed new indication for dutasteride and the change to the labeling of finasteride, both of which were intended to permit physicians to use the drugs for chemoprevention. Finally, we discuss future directions for 5-ARI research.

Expression of liver-specific member of the 3β-hydroxysteroid dehydrogenase family, an isoform possessing an almost exclusive 3-ketosteroid reductase activity

We have recently characterized two types of rat 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3β-HSD) isoenzymes expressed in adrenals and gonads. In addition, we have cloned a third type of cDNA encoding a predicted type III 3β-HSD protein specifically expressed in the male rat liver which shares 80% similarity with the two other isoenzymes. Transient expression in human HeLa cells of the cDNAs reveals that the type III 3β-HSD protein does not display oxidative activity for the classical substrates of 3β-HSD, in contrast to the type I 3β-HSD isoenzyme. However, in the presence of NADH, type III isoenzyme, in common with the type I isoform, converts 5α-androstane-3,17-dione (A-dione) and 5α-dihydrotestosterone (DHT) to the corresponding 3β-hydroxysteroids. In fact, the type I and the type III isoenzymes have the same affinity for DHT with K(m) values of 5.05 and 6.16 μM, respectively. When NADPH is used as cofactor, the affinity for DHT of the type III isoform becomes higher than that of the type I isoform with K(m) values of 0.12 and 1.18 μM, respectively. The type III isoform is thus a 3-ketoreductase using NADPH as preferred cofactor which is responsible for the conversion of 3-keto-saturated steroids such as DHT and A-dione into less active steroids.

Family-based investigation of the C677T polymorphism of the methylenetetrahydrofolate reductase gene in ischaemic heart disease

Background: Elevated homocysteine is associated with ischaemic heart disease (IHD). The C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene results in reduced MTHFR enzyme activity and reduced methylation of homocysteine to methionine resulting in mild hyperhomocysteinaemia. Case-control association studies of the role of the C677T MTHFR polymorphism in IHD have produced conflicting results. We therefore used newly described family-based association tests to investigate the role of this polymorphism in IHD, in a well-defined population. Methods: A total of 352 individuals from 129 families (discordant sibships and parent-child trios) were recruited. Linkage disequilibrium between the polymorphism and IHD was tested for using the combined transmission disequilibrium test (TDT)/sib-TDT and pedigree disequilibrium test (PDT). Homocysteine levels were measured. Results: Both the TDT/sib-TDT and PDT analyses found a significantly reduced transmission of the T allele to affected individuals (P=0.016 and P=0.021). There was no significant difference in homocysteine levels between affected and unaffected siblings. TT homozygotes had mean homocysteine levels significantly higher than those of TC heterozygotes (P

Impaired functioning of thermolabile methylenetetrahydrofolate reductase is dependent on riboflavin status: implications for riboflavin requirements.

BACKGROUND: Methylenetetrahydrofolate reductase (MTHFR; EC 1.7.99.5) supplies the folate needed for the metabolism of homocysteine. A reduction in MTHFR activity, as occurs in the homozygous state for the 677C-->T (so-called thermolabile) enzyme variant (TT genotype), is associated with an increase in plasma total homocysteine (tHcy). OBJECTIVE: In vitro studies suggest that the reduced activity of thermolabile MTHFR is due to the inappropriate loss of its riboflavin cofactor. We investigated the hypothesis that MTHFR activity in the TT genotype group is particularly sensitive to riboflavin status. DESIGN: We studied tHcy and relevant B-vitamin status by MTHFR genotype in a cross-sectional study of 286 healthy subjects aged 19-63 y (median: 27 y). The effect of riboflavin status was examined by dividing the sample into tertiles of erythrocyte glutathionine reductase activation coefficient, a functional index of riboflavin status. RESULTS: Lower red blood cell folate (P = 0.0001) and higher tHcy (P = 0.0082) concentrations were found in the TT group than in the heterozygous (CT) or wild-type (CC) groups. However, these expected relations in the total sample were driven by the TT group with the lowest riboflavin status, whose mean tHcy concentration (18.09 micromol/L) was almost twice that of the CC or CT group. By contrast, adequate riboflavin status rendered the TT group neutral with respect to tHcy metabolism. CONCLUSIONS: The high tHcy concentration typically associated with homozygosity for the 677C-->T variant of MTHFR occurs only with poor riboflavin status. This may have important implications for governments considering new fortification policies aimed at the prevention of diseases for which this genotype is associated with increased risk.

Nitrate reductase activity in macroalgae and its vertical distribution in macroalgal epiphytes of seagrasses.

Macroalgal epiphytes within seagrass meadows make a significant contribution to total primary production by assimilating water column N and transferring organic N to sediments. Assimilation of NO3 – requires nitrate reductase (NR, EC 1.6.6.1); NR activity represents the capacity for NO3 – assimilation. An optimised in vitro assay for determining NR activity in algal extracts was applied to a wide range of macroalgae and detected NR activity in all 22 species tested with activity 2 to 290 nmolNO3 – min–1 g–1 frozen thallus. With liquid-N2 freezing immediately after sample collection, this method was practical for estimating NR activity in field samples. Vertical distribution of NR activity in macroalgal epiphytes was compared in contrasting Posidonia sinuosa and Amphibolis antarctica seagrass meadows. Epiphytes on P. sinuosa had higher mass-specific NR activity than those on A. antarctica. In P. sinuosa canopies, NR activity increased with distance from the sediment surface and was negatively correlated with [NH4 +] in the water but uncorrelated with [NO3 –]. This supported the hypothesis that NH4 + released from the sediment suppresses NR in epiphytic algae. In contrast, the vertical variation in NR activity in macroalgae on A. antarctica was not statistically significant although there was a weak correlation with [NO3 –], which increased with distance from the sediment. Estimated capacities for NO3 – assimilation in macroalgae epiphytic on seagrasses during summer (24 and 46 mmolN m–2 d–1 for P. sinuosa and A. antarctica, respectively) were more than twice the estimated N assimilation rates in similar seagrasses. When the estimates were based on annual average epiphyte loads for seagrass meadows in other locations, they were comparable to those of seagrasses. We conclude that epiphytic algae represent a potentially important sink for water-column nitrate within seagrass meadows.

Familial idiopathic methemoglobinemia revisited: original cases reveal 2 novel mutations in NADH cytochrome b5 reductase

In 1943, the first description of familial idiopathic methemoglobinemia in the United Kingdom was reported in 2 members of one family. Five years later, Quentin Gibson (then of Queen's University, Belfast, Ireland) correctly identified the pathway involved in the reduction of methemoglobin in the family, thereby describing the first hereditary trait involving a specific enzyme deficiency. Recessive congenital methemoglobinemia (RCM) is caused by a deficiency of reduced nicotinamide adenine dinucleotide (NADH)-cytochrome b5 reductase. One of the original propositi with the type 1 disorder has now been traced. He was found to be a compound heterozygote harboring 2 previously undescribed mutations in exon 9, a point mutation Gly873Ala predicting a Gly291Asp substitution, and a 3-bp in-frame deletion of codon 255 (GAG), predicting loss of glutamic acid. A brother and a surviving sister are heterozygous; each bears one of the mutations. Thirty-three different mutations have now been recorded for RCM. The original authors' optimism that RCM would provide material for future genetic studies has been amply justified.