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PubMed2000

Fads and fashion.

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Education, Professional↗
PubMed2000

Lysosomal prenylcysteine lyase is a FAD-dependent thioether oxidase.

Prenylated proteins contain either a 15-carbon farnesyl or a 20-carbon geranylgeranyl isoprenoid covalently attached via a thioether bond to a cysteine residue at or near their C terminus. As prenylated proteins comprise up to 2% of the total protein in eukaryotic cells, and the thioether bond is a stable modification, their degradation raises a metabolic challenge to cells. A lysosomal enzyme termed prenylcysteine lyase has been identified that cleaves prenylcysteines to cysteine and an unidentified isoprenoid product. Here we show that the isoprenoid product of prenylcysteine lyase is the C-1 aldehyde of the isoprenoid moiety (farnesal in the case of C-15). The enzyme requires molecular oxygen as a cosubstrate and utilizes a noncovalently bound flavin cofactor in an NAD(P)H-independent manner. Additionally, a stoichiometric amount of hydrogen peroxide is produced during the reaction. These surprising findings indicate that prenylcysteine lyase utilizes a novel oxidative mechanism to cleave thioether bonds and provide insight into the unique role this enzyme plays in the cellular metabolism of prenylcysteines.

Carbon-Sulfur Lyases↗
PubMed2002

Probiotics and inflammatory bowel disease: from fads and fantasy to facts and future.

Probiotic therapy is attracting the renewed interest of clinicians and basic investigators from a variety of traditional research disciplines. While the theoretical rationale for modifying the commensal flora of the gastrointestinal tract in specific circumstances appears sound and requires scientific pursuit, the field of probiotics has been clouded by exaggerated claims from some quarters. In general, many of the claims for therapeutic efficacy have not been well substantiated, but the field is now poised for evaluation within the realm of evidence-based medicine. Alterations in commensal bacterial flora within the gastrointestinal tract are associated with susceptibility to pathogens such as Clostridium difficile and there is persuasive evidence that the normal flora may participate in the pathogenesis of inflammatory bowel disease and other chronic diseases in genetically susceptible individuals. This has prompted various strategies to fortify or otherwise modify the enteric flora by dietary supplements containing probiotic formulations. Detailed comparisons of probiotic performance amongst different bacterial strains have not been performed in vivo in man or under clinical trial conditions, and the level of scientific characterisation of individual organisms has been variable. In addition, it cannot be assumed that the same probiotic is equally suitable for all individuals. Moreover, the heterogeneity of clinical disorders such as Crohn's disease and ulcerative colitis implies that strain-specific properties may be required for subset-specific categories of patients. While cocktails of probiotics offer convenience, therapeutic progress may require clarification of the mechanism of probiotic action and may be delayed until individual bacterial components have been rigorously studied. More importantly, the full potential of therapeutic manipulation of the enteric flora with probiotics or other strategies may not be optimally realised until the composition and metabolic activities of the normal flora are better understood.

Digestive System↗
PubMed2006

Fads and foibles in ART: where is the evidence?

This commentary on the scientific basis of laboratory procedures in assisted conception discusses the origins of widespread discrepancies in 'standard' laboratory techniques experienced by patients and their embryos. The lack of direct evidence from clinical laboratory trials and the reasons for this will be highlighted using some examples drawn mainly from embryo culture. Inconsistencies and grey areas in the governance framework of this unique field could usefully be eliminated and attention focused on the need for a rational approach to procedural trials and pilot studies necessarily conducted in clinical laboratories. This may help progress towards a consensus on fundamental questions for which the evidence is currently lacking.

Clinical Trials as Topic↗
PubMed2002

Hitchhiking fads en route to peroxisomes.

A unique aspect of protein translocation across the peroxisomal membrane is that folded and oligomeric proteins get across this membrane (Purdue and Lazarow, 2001). The generality of this rule, its specific features, and its mechanism are not fully understood. A paper in this issue addresses, in a very thorough fashion, the assembly, cofactor binding, and import of an oligomeric protein, acyl-CoA oxidase (Aox), into the peroxisome matrix (Titorenko et al., 2002, this issue).

Acyl-CoA Oxidase↗
PubMed1986

A novel FAD-protein that allows effective reduction of methyl viologen by NADH (NADH-methyl viologen reductase) from photosynthetic bacterium, Rhodospirillum rubrum: purification and characterization.

It was found that the cytoplasm of light-grown cells of Rhodospirillum rubrum could catalyze the reduction of methyl viologen (MV) (Em, 7 = -0.44 V) by NADH and NADPH. In the present study, the enzyme capable of catalyzing MV reduction by NADH (NADH-MV reductase) was purified 1,500-fold from an extract of cells with a yield of 4.4%. The purification procedure comprised (NH4)2SO4 fractionation, and chromatographies on Sepharose CL-6B, DEAE-Sepharose CL-6B, phenyl-Sepharose CL-4B, Blue-Cellulofine, and TSK-Gel G3000SW. Two NADPH-MV reductases were separated during the purification. The NADH-MV reductase obtained was nearly homogeneous, as judged on polyacrylamide gel electrophoresis both in the presence and absence of sodium dodecyl sulfate. The enzyme has a molecular weight of 220,000 and an isoelectric point of 4.8; it is composed of four subunits with a molecular weight of 57,000, and is bound with about 1 mol FAD/mol subunit. The activity is optimum at pH 8. The Km values for NADH and MV are 115 microM and 1.3 mM, respectively, with a molecular activity of 13,000 min-1. The activity was stimulated 2.4-fold in the presence of 20-100 mM ammonium ions. The enzyme also catalyzed the reduction of benzyl viologen, methylene blue and 2,6-dichlorophenol-indophenol (Em, 7 = -0.36, +0.011, and +0.217 V, respectively) at comparable rates. The ratios of the activity with NADH to that with NADPH were 80, 133, 41, and 5.5 with MV, benzyl viologen, methylene blue and 2,6-dichlorophenolindophenol, respectively. The enzyme was significantly stable in the presence of both 5mM 2-mercaptoethanol and 20% (w/v) glycerol. The activity was not appreciably influenced by the presence of 2 M urea, although the reagent caused dissociation to the subunits.

Chromatography↗
PubMed2005

Spectroscopic analysis of the dark relaxation process of a photocycle in a sensor of blue light using FAD (BLUF) protein Slr1694 of the cyanobacterium Synechocystis sp. PCC6803.

Slr1694 is a BLUF (sensor of blue light using flavin adenine dinucleotide) protein and a putative photoreceptor in the cyanobacterium Synechocystis sp. PCC6803. Illumination of Slr1694 induced a signaling light state concurrent with a red shift in the UV-visible absorption of flavin, and formation of the bands from flavin and apo-protein in the light-minus-dark Fourier transform infrared (FTIR) difference spectrum. Replacement of Tyr8 with phenylalanine abolished these changes. The light state relaxed to the ground dark state, during which the FTIR bands decayed monophasically. These bands were classifiable into three groups according to their decay rates. The C4=O stretching bands of a flavin isoalloxazine ring had the highest decay rate, which corresponded to that of the absorption red shift. The result indicated that the hydrogen bonding at C4=O is responsible for the UV-visible red shift, consistent with the results of density functional calculation. All FTIR bands and the red shift decayed at the same slower rate in deuterated Slr1694. These results indicated that the dark relaxation from the light state is limited by proton transfer. In contrast, a constrained light state formed under dehydrated conditions decayed much more slowly with no deuteration effects. A photocycle mechanism involving the proton transfer was proposed.

Bacterial Proteins↗
PubMed1979

Lip adhesion--a passing fad?

Lip adhesion before a definitive cleft palate repair has received recent attention, and is being advocated for use in more cases. The presumed benefits are cited. Are these benefits exaggerated or misrepresented? What about the disadvantages? The author believes a more critical appraisal of the advantages and more awareness of the possible disadvantages are in order.

Cleft Lip↗