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At least 379 records · Page 21Linked to original sources
PubMed1995

L-lactate oxidase and L-lactate monooxygenase: mechanistic variations on a common structural theme.

Properties of L-lactate oxidase from Aerococcus viridans are described. The gene encoding the enzyme has been isolated. From its cDNA sequence the amino acid sequence has been derived and shown to have high similarity with those of other enzymes catalyzing oxidation of L-alpha-hydroxy acids, including flavocytochrome b2, lactate monooxygenase, glycolate oxidase, mandelate dehydrogenases and a long chain alpha-hydroxy acid oxidase. The enzyme is expressed in Escherichia coli, and is a flavoprotein containing FMN as prosthetic group. It shares many properties of other alpha-hydroxy acid oxidizing enzymes, eg stabilization of the anionic semiquinone form of the flavin, facile formation of flavin-N(5)-sulfite adducts and a set of conserved amino acid residues around the bound flavin. Steady-state and rapid reaction kinetics of the enzyme have been studied and found to share many characteristics with those of L-lactate monooxygenase, but to differ from the latter in quantitative aspects. It is these quantitative differences between the two enzymes which account for the differences in the overall reactions catalyzed. These differences arise from different stabilities of a common intermediate of reduced flavin enzyme and pyruvate. In the case of the monooxygenase this complex is very stable and is the form that reacts with O2 to give a complex in which the oxidative decarboxylation occurs, yielding the products, acetate, CO2, and H2O (Lockridge O, Massey V, Sullivan PA (1972) J Biol Chem 247, 8097-8106). With lactate oxidase, the complex dissociates rapidly, with the result that it is the free reduced flavin form of the enzyme that reacts with O2, to give the observed products, pyruvate and H2O2.

Amino Acid Sequence↗
PubMed1994

The short-chain alcohol dehydrogenase superfamily: variations on a common theme.

Multiple alignment of members of the short-chain alcohol dehydrogenase (SCAD) superfamily, according to the conserved domains A-F, has revealed a number of important relationships. It can be shown that the 17 beta-hydroxysteroid dehydrogenase type 2 enzyme is more closely related to D-beta-hydroxybutyrate dehydrogenase than it is to 17 beta-hydroxysteroid dehydrogenase type 1. Carbonyl reductase, previously considered to be a member of the aldo-keto reductase superfamily, displayed high homology in the conserved domains and is clearly part of the SCAD superfamily despite the insertion of a large peptide between conserved domains. Alignment of the product of the Leishmania methotrexate resistance gene HMTX showed that an internal, highly conserved domain can be substituted by an unrelated sequence without loss of biological activity. Furthermore, comparisons of the chimeric trifunctional enzyme enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase/3-hydroxyacyl-CoA epimerase with other family members suggests that the region between the conserved B and C domains is the last to diverge between closely related enzymes and that the F domain appears to evolve with a different evolutionary clock to the rest of the protein. Finally, a highly conserved pattern of serine and threonine residues in the active site of SCAD enzymes indicates that these residues may play an important role in catalysis. These observations should facilitate alignment of future members of the SCAD superfamily.

17-Hydroxysteroid Dehydrogenases↗
PubMed1991

Photosynthetic reaction centres: variations on a common structural theme?

From their hybrid properties, the reaction centres of green sulphur bacteria and heliobacteria seem to be the missing links between the two branches of the reaction centre family, typified by higher plant photosystem I and the purple bacterial reaction centre. This suggests that all of the diverse types of photosynthetic reaction centres have closer structural resemblances than was previously thought.

Bacterial Physiological Phenomena↗
PubMed2000

The sevenless signaling pathway: variations of a common theme.

Many developmental processes are regulated by intercellular signaling mechanisms that employ the activation of receptor tyrosine kinases. One model system that has been particular useful in determining the role of receptor tyrosine kinase-mediated signaling processes in cell fate determination is the developing Drosophila eye. The specification of the R7 photoreceptor cell in each ommatidium of the developing Drosophila eye is dependent on activation of the Sevenless receptor tyrosine kinase. This review will focus on the genetic and biochemical approaches that have identified signaling molecules acting downstream of the Sevenless receptor tyrosine kinase which ultimately trigger differentiation of the R7 photoreceptor cell.

Animals↗
PubMed1998

Glucocorticoid signalling--multiple variations of a common theme.

Recent advances in molecular genetics have brought us closer to answering the question as to which mechanisms are used by steroid hormone receptors to control transcription. While binding to specific response elements in the promoter and enhancer regions of many genes has for a long time been considered as the major mode of action, a growing number of alternative transcriptional control mechanisms have been identified in the last couple of years. With the recent finding that DNA binding of the glucocorticoid receptor is not essential for survival, mechanisms depending on cross-talk with other transcription factors through protein-protein interactions have gained attention. In this mini-review, we will discuss the roles of DNA binding-dependent and -independent transcriptional modes of action in development and physiology as exemplified by the analysis of glucocorticoid receptor function.

Adrenal Glands↗
PubMed1997

The aconitase family: three structural variations on a common theme.

The aconitase family contains a diverse group of iron-sulphur (Fe-S) isomerases and two types of iron regulatory protein (IRP). Structural comparisons have revealed three architecturally distinct variants in which one of the four structural domains is covalently linked at either the amino- or carboxy-terminal end of a single polypeptide or else this domain exists as an independent subunit.

Aconitate Hydratase↗
PubMed2005

RNA and protein folding: common themes and variations.

Visualizing the navigation of an ensemble of unfolded molecules through the bumpy energy landscape in search of the native state gives a pictorial view of biomolecular folding. This picture, when combined with concepts in polymer theory, provides a unified theory of RNA and protein folding. Just as for proteins, the major folding free energy barrier for RNA scales sublinearly with the number of nucleotides, which allows us to extract the elusive prefactor for RNA folding. Several folding scenarios can be anticipated by considering variations in the energy landscape that depend on sequence, native topology, and external conditions. RNA and protein folding mechanism can be described by the kinetic partitioning mechanism (KPM) according to which a fraction (Phi) of molecules reaches the native state directly, whereas the remaining fraction gets kinetically trapped in metastable conformations. For two-state folders Phi approximately 1. Molecular chaperones are recruited to assist protein folding whenever Phi is small. We show that the iterative annealing mechanism, introduced to describe chaperonin-mediated folding, can be generalized to understand protein-assisted RNA folding. The major differences between the folding of proteins and RNA arise in the early stages of folding. For RNA, folding can only begin after the polyelectrolyte problem is solved, whereas protein collapse requires burial of hydrophobic residues. Cross-fertilization of ideas between the two fields should lead to an understanding of how RNA and proteins solve their folding problems.

Animals↗
PubMed1999

Association of pre-eclampsia with common coding sequence variations in the lipoprotein lipase gene.

Marked dyslipidemia may contribute to endothelial cell dysfunction in pre-eclampsia. Carriers of N291S or D9N missense mutations in the lipoprotein lipase (LPL) gene exhibit reductions in LPL activity and are predisposed to dyslipidemia and cardiovascular disease. In Caucasians, the D9N variant is in strong linkage disequilibrium with the - 93T --> G promoter variant. A fourth LPL variant, S447X, is often associated with a beneficial lipid profile. We asked if the N291S and the combination D9N/- 93T --> G variants are more prevalent, and if the S447X variant is less prevalent, in Caucasian women with pre-eclampsia as compared with normal pregnancies. DNA amplification was followed by an allele-specific oligonucleotide ligation assay. Allele frequencies were analyzed with a chi2 table and Yates' correction. The N291S variant was identified in 11.1% of pre-eclamptics as compared with 2.9% of pregnancy controls (p = 0.008). All carriers of D9N were also carriers of - 93T --> G. The D9N/ - 93T --> G combined variant was found in 7.1% of pre-eclamptics as compared with 1.4% of pregnancy controls (p = 0.02). No individuals were carriers of both N291S and D9N/ - 93T --> G. Thus, 18.2% of pre-eclamptics had either of these LPL mutations compared with 4.3% of pregnancy controls (and 4.4% of population controls). The frequency of the S447X variant did not differ among groups. We conclude that carriers of N291S or combined D9N/ - 93T --> G mutations in the LPL gene are at substantially increased risk of pre-eclampsia.

Adult↗
PubMed2000

Procyanidin content and variation in some commonly consumed foods.

Procyanidins are a subclass of flavonoids found in commonly consumed foods that have attracted increasing attention due to their potential health benefits. However, little is known regarding their dietary intake levels because detailed quantitative information on the procyanidin profiles present in many food products is lacking. Therefore, the procyanidin content of red wine, chocolate, cranberry juice and four varieties of apples has been determined. On average, chocolate and apples contained the largest procyanidin content per serving (164.7 and 147.1 mg, respectively) compared with red wine and cranberry juice (22.0 and 31.9 mg, respectively). However, the procyanidin content varied greatly between apple samples (12.3-252.4 mg/serving) with the highest amounts on average observed for the Red Delicious (207.7 mg/serving) and Granny Smith (183.3 mg/serving) varieties and the lowest amounts in the Golden Delicious (92.5 mg/serving) and McIntosh (105.0 mg/serving) varieties. The compositional data reported herein are important for the initial understanding of which foods contribute most to the dietary intake of procyanidins and may be used to compile a database necessary to infer epidemiological relationships to health and disease.

Biflavonoids↗
PubMed1987

Immunological variation in the 'common region' of the T antigens of polyoma virus.

Characterization of a series of mouse monoclonal antibodies (designated alpha Py C21 to 26) against the region common to the large, middle and small T antigens of polyoma virus has revealed immunological diversities among the N termini of these antigens. Four of the antibodies (alpha Py C21 to 24) appeared to recognize all the T antigens present in lytically infected cells, but two of them (alpha Py C25, 26) failed to immunoprecipitate small T antigen either from 35S- or 32P-labelled cells and recognized only a subset of middle and large T antigens. None of the antibodies recognized the protein kinase activity normally associated with middle T antigen or the 60K mol. wt. antigen-related protein observed in polyoma virus lytically infected or transformed cells. The possible immunodominance of the N termini of the early gene products (as well as VP1) in the natural host of polyoma virus and the observed antigenic heterogeneity are considered.

Antibodies, Monoclonal↗
PubMed2003

Eukaryotic-type protein kinases in Streptomyces coelicolor: variations on a common theme.

The increasing number of genes encoding eukaryotic-type Ser/Thr protein kinases (ESTPKs) in prokaryotes, identified mostly due to genome-sequencing projects, suggests that these enzymes play an indispensable role in many bacterial species. Some prokaryotes, such as Streptomyces coelicolor, carry numerous genes of this type. Though the regulatory pathways have been intensively studied in the organism, experimental proof of the physiological function of ESTPKs is scarce. This review presents a family portrait of the genes identified in the sequence of the S. coelicolor A3(2) genome. Based on the available experimental data on ESTPKs in streptomycetes and related bacteria, and on computer-assisted sequence analyses, possible roles of these enzymes in the regulation of cellular processes in streptomycetes are suggested.

Amino Acid Sequence↗
PubMed2000

Generalized variational principle for the time-dependent Hartree-Fock equations for a Slater determinant

The time-dependent Hartree-Fock equations are derived from a variational principle for the general N-body action of a Slater determinant of single-electron orbitals. The variational principle generalizes commonly used variational treatments based on reduced two-body actions. The self-consistent field equations are found to contain time-dependent corrections to the standard mean-field interactions. Their physical significance is discussed and a time-dependent phase shift to the Slater determinant is obtained that properly accounts for the total interaction energy in the mean-field approach.

Journal Article↗
PubMed1992

Diversity in cellular signaling for nerve growth factor and insulin: variations on a common theme.

Numerous similarities exist in the cellular signaling events observed for insulin and nerve growth factor. Because the two hormones share many functional properties, and exhibit similar effects on neurons, the possibility of common early signaling events has been explored. Many studies have focused on the important role of protein phosphorylation. Two distinct but related mechanisms are discussed that may mediate, in part, the ability of these two hormones to regulate the activities of protein kinases and phosphatases.

Amino Acid Sequence↗
PubMed2006

Anatomical variations of the common carotid artery bifurcation.

BACKGROUND: The correlation of the common carotid artery (CCA) bifurcation and its surrounding structures is poorly described. The aim of this study was to describe the anatomy of the CCA bifurcation relative to its surrounding structures. METHOD: We dissected a total of 67 carotid specimens from 36 embalmed cadavers. CCA bifurcation occurred at the superior border of thyroid cartilage in 39% and at the body of hyoid bone in 40% of specimens. RESULTS: The superior thyroid artery arose more commonly from the CCA (52.3%) than the external carotid artery (46.2%). The vagus nerve was posterior to the carotid bifurcation in 40 (60%), posterior-lateral in 24 (36%), posterior-medial in 2 (3%) and anterior-lateral in 1 specimen (1.5%). The hypoglossal nerve was closer to the CCA bifurcation when the CCA bifurcated at the level of the hyoid bone than when it bifurcated at the superior border of the thyroid cartilage (P < 0.05). The correlation of the common facial vein and the carotid artery was highly variable. CONCLUSION: The presence of a high CCA bifurcation should caution surgeons that the hypoglossal nerve lies in closer proximity and is more vulnerable. Preoperatively documenting the level of the CCA bifurcation may be helpful in identifying those patients at increased risk of iatrogenic injury.

Aged↗