Riboflavin:A multifunctional vitamin.

Riboflavin, a component of the B-2 vitaminic complex, plays important roles in biochemistry, especially in redox reactions, due to the ability to participate in both one- and two-electron transfers as well as acting as a photosensitizer. Accordingly, low intakes of this vitamin have been associated with different diseases, including cancer and cardiovascular diseases. Riboflavin is thought to contribute to oxidative stress through its capacity to produce superoxide but, interestingly, it can also promote the reduction of hydroperoxides. This peculiar and multifunctional behavior allows riboflavin to take part in various biochemical pathways as a nucleophile and an electrophile, turning it into a versatile and important biological compound

Ole J. Benedictow: What Disease was Plague? On the Controversy over the Microbiological Identity of Plague Epidemics of the Past. Leiden, Brill, 2010.

At low concentrations, dimethyl sulfoxide (DMSO) stimulated the avian myeloblastosis virus reverse transcriptase activity. About 40% stimulation was obtained in the presence of 5% (v/v) DMSO, using activated DNA and polyriboadenylic acid (poly(rA)) as templates, and Mg2+ as divalent cation. A similar stimulation by DMSO was observed with Mn2+ for the poly(rA)-dependent reverse transcriptase activity. DMSO at concentrations higher than 15% inhibited the reverse transcriptase reactions, independent of the template-primers used. An exception was detected with the 2'-fluoro analog of poly(rA) as template, where an activation of 100% was found in the presence of 20% DMSO. The stimulation caused by DMSO could be due to a reduction of the apparent Km value for poly(rA) from 9.1 to 3.3 mu g/ml

INHIBITION OF DNA-POLYMERASE ALPHA AND REVERSE-TRANSCRIPTASE ACTIVITIES BY HPA-23

We describe the effect of HPA-23 in the DNA synthesis reaction catalyzed by DNA polymerase-alpha and reverse transcriptase. 0.085 and 0.017-mu-M of HPA-23 inhibited 50% of DNA polymerase alpha-activity in the presence of activated DNA and poly(dA)-oligo(dT), respectively. However, for reverse transcriptase, this same effect was observed only with 6.76-mu-M of the drug independently of the template-primer used (activated DNA or poly (rA)-oligo(dT)). HPA-23 was a non-competitive inhibitor with respect to activated DNA and to TTP in the DNA polymerase alpha-reaction.344173245946

INHIBITION OF THE WHEAT-GERM DNA POLYMERASE-A ACTIVITY BY THE ANTIVIRAL DRUG HPA-23

Wheat germ DNA polymerase A, a gamma-like enzyme, recognized efficiently natural and synthetic RNA templates, resembling a retroviral reverse transcriptase (P. Laquel et al., Biochim Biophys Acta 1048 (1990):139-148). Ammonium-21-tungsto-9-antimoniate (HPA-23), an antiviral drug, inhibited the DNA polymerase A activities, independently of the template primers used, i.e. activated DNA or polyriboadenylic acid oligodeoxythymidylate (poly(rA)-oligo(dT)). The inhibition observed in the poly(rA)-oligo(dT)-directed DNA polymerase A activity occurred in the presence of either Mg2+, or Mn2+ as divalent cation, and also with the 2'-fluoro analogue of poly(rA) as template. HPA-23 was a noncompetitive inhibitor with respect to TTP, activated DNA, poly(rA)-oligo(dT), and poly(dAfl)-oligo(dT). A preincubation study showed a reversible HPA-23 binding to DNA polymerase A, in the presence of poly(rA)-oligo(dT) as the template primer.2351055106

Bovine kidney low molecular weight acid phosphatase: FMN-dependent kinetics.

A low molecular weight bovine kidney acid phosphatase, electrophoretically homogeneous and with a relative molecular mass of 17.8 kDa, was used in this work. Among the various substrates tested, FMN was found to be the most effective, at pH 7.0. Distinct activation energy values were obtained for nitrophenyl phosphate- (45.44 kJ mol(-1)) and flavin mononucleotide- (28.60 kJ mol-1) hydrolysis reactions. The FMN hydrolysis was strongly inhibited by Cu2+ and pCMB, but activated by guanosine. Pyridoxal-phosphate and vanadate were competitive inhibitors for the FMN-dependent reaction.4161201120

Inhibition of reverse transcriptase activity of HIV by polysaccharides of brown algae

Brown algae have two kinds of acid polysaccharides present in the extracellular matrix: sulfated fucan and alginic acid. We have previously isolated and characterized fucans from several species of brown seaweed. The characterized fucans from Dictyotaceae are heterofucans containing mainly fucose, galactose, glucose, xylose, and/or uronic acid. The fucan from Fucus vesiculosus is a homofucan containing only sulfated fucose. We assessed the activity of these fucans as inhibitors of HIV from reverse transcriptase (RT). Using activated DNA and template primers poly(rA)-oligo(dT), we found that fucans at a concentration of 0.5-1.0 mu g/mL had a pronounced inhibitory effect in vitro on the avian reverse transcriptase, with the exception of xylogalactofucan isolated from Spatoglossum schroederi, which had no inhibitory activity. The alginic acid (1.0 mu g/mL) inhibited the reverse transcriptase activity by 51.1% using activated DNA. The inhibitory effect of fucans was eliminated by their desulfation. Furthermore, only xylofucoglucuronan from S. schroederi lost its activity after carboxyreduction. We suggest that fucan activity is not only dependent on the ionic changes but also on the sugar rings that act to spatially orientate the charges in a configuration that recognizes the enzyme, thus determining the specificity of the binding. (C) 2008 Elsevier Masson SAS. All rights reserved.62530330