Heterooligomers of the muscarinic receptor and G proteins purified from porcine atria

Muscarinic receptor extracted from porcine atria in digitonin-cholate copurified with Gα_o, Gα_i1-3, and caveolins. The presence of complexes was confirmed by coimmunoprecipitation of the receptor, α-subunits, and caveolins in various combinations. Homooligomers of α_i2 were detected on Western blots, and heterooligomers of α_i2 and α_o were identified by coimmunoprecipitation; thus, a complex may contain at least two α-subunits. Other combinations of α-subunit were not detected. The ratio of total α-subunit to receptor was near 1, as measured by [³⁵S]GTPγS and the antagonist [³H]quinuclidinylbenzilate, and the binding of [³⁵S]GTPγS was manifestly biphasic. The ratio of α_o to α_i1,2 also was near 1, as determined from the intensity of Western blots. Cardiac muscarinic receptors therefore can be purified as a mixture of complexes that contain caveolins and oligomers of α-subunit, some of which are heteromeric. Each complex would appear to contain equal numbers of α-subunit and the receptor.     

Synthesis of selenocysteine and its derivatives with an emphasis on selenenylsulfide (-Se-S-) formation

A short survey of historic and current methods for the synthesis of selenocysteine, selenocystine, and derivatives and related compounds is presented, with an additional emphasis on the formation of selenocysteine-derived Se-S bridges. The majority of methods to the amino acid starts with protected and O-activated serine, but also other concepts are included such as radical or multicomponent strategies, the latter allowing also direct access to peptoids in one pot. Of special importance is the monomeric oxidative cyclization of selenocysteine-cysteine peptides to eight-membered and larger rings with a selenenylsulfide bridge, a crucial element in several selenoproteins.     

Galloylated catechins and stilbene diglucosides in Vitis vinifera cell suspension cultures

Suspension cultures of Vitis vinifera were found to produce catechins and stilbenes. When cells were grown in a medium inducing polyphenol synthesis, (−)-epicatechin-3-O-gallate, dimeric procyanidin B-2 3′-O-gallate and two resveratrol diglucosides were isolated, together with a new natural compound that was identified as cis-resveratrol-3,4′-O-β-diglucoside by spectroscopical methods.     

Solution equilibria leading to the formation of metal-metal bonds in partially oxidized bisoxalatoplatinate(II) systems

The reaction between [Pt^II(Ox)₂]²⁻ and an appropriate oxidant resulted in the formation of the dimeric unbridged platinum complex [{Pt^III(Ox)₂ }₂]²⁻ where (Ox) is oxalate. This complex was moderately stable under ambient conditions and was studied via a variety of NMR and spectrophotometric techniques. Reaction of the [{Pt^III(Ox)₂}₂]²⁻ complex with [Pt^II(Ox)₂]²⁻ in the presence of H⁺ lead to the formation of a series of longer platinum oligomers with non-integral oxidation states, culminating in the formation of partially oxidized platinum polymers of general formula [{Pt(Ox)₂}_n]ⁿ⁻. The concentration of H⁺ was an important factor leading to higher oligomers and the approximate number of protons associated with each oligomer was determined. The analogous [{Pt^III(Mal)₂}₂]²⁻ complex, where (Mal) is the malonate anion, was also synthesized and studied but was shown to be significantly less stable.     

History of aquatic invertebrate invasions in the Caspian Sea

Incorporation of the fossil record and molecular markers into studies of biological invasions provides new historical perspectives on the incidence of natural and human-mediated invasions of nonindigenous species (NIS). Palaeontological, phylogeographic, and molecular evidence suggests that the natural, multiple colonizations of the Caspian basin via transient connections with the Black Sea and other basins played an important role in shaping the diversity of Caspian fauna. Geographically isolated, conspecific Ponto-Caspian lineages that currently inhabit fragmented habitats in the Ponto-Caspian region show limited genetic divergence, implying geologically recent episodes of gene flow between populations during the Pliocene to Pleistocene. Several molluscan lineages in the Caspian Sea may have descended from Lake Pannon stock before the Late Miocene isolation of the Caspian depression, about 5.8 million years ago. Anthropogenic activities during the 20th century were responsible for a 1800-fold increase in the rate of establishment of new aquatic species in the Caspian Sea compared to the preceding two million years of natural colonization. The observed success of NIS invasions during the 20th century was due primarily to human-mediated transport mechanisms, which were dominated by shipping activities (44%). Human-mediated species transfer has been strongly asymmetrical, toward the Volga Delta and Caspian Sea from or through Black and Azov Seas. Global and regional trade, particularly that mediated by commercial ships, provides dispersal opportunities for nonindigenous invertebrates, indicating that future invasions in the Caspian Sea are anticipated.     

The multifaceted regulation and functions of PKM2 in tumor progression

Tumor cells undergo metabolic rewiring from oxidative phosphorylation towards aerobic glycolysis to maintain the increased anabolic requirements for cell proliferation. It is widely accepted that specific expression of the M2 type pyruvate kinase (PKM2) in tumor cells contributes to this aerobic glycolysis phenotype. To date, researchers have uncovered myriad forms of functional regulation for PKM2, which confers a growth advantage on the tumor cells to enable them to adapt to various microenvironmental signals. Here the richness of our understanding on the modulations and functions of PKM2 in tumor progression is reviewed, and some new insights into the paradoxical expression and functional differences of PKM2 in distinct cancer types are offered.     

Absorption and magnetic circular dichroism of chlorophyll a and b dimers

The dimerization of chlorophyll a to the so-called special pair, in which the two monomers are linked together by two nucleophilic molecules (alcohol or water), leads to shifts and splittings of the absorption and magnetic circular dichroism (MCD) spectral bands. The changes in the Q-band region are described starting from a model proposed previously (L.L. Shipman. J.R. Morris and J.J. Katz. J. Phys. Chem. 80 (1976) 877). and which we extended to include the MCD. The parameters alpha(x) and alpha(y), containing the exciton and environmental parameters (L.L. Shipman. J.R. Norris and J.J. Katz, J. Phys. Chem. 80 (1976) 877) and the relative orientation of the monomers in the dimer, determine the spectral features. Spectral simulation leads to the conclusion that in the special pair alpha(x) and alpha(y), are in the region of 0.6-0.8 and that the dimer has C2 symmetry. The model was also applied to the case of the pure dimer of chlorophyll b where the monomers are bound together directly. With similar values for alpha(x) and alpha(y) the spectra could be reconstructed assuming almost parallel monomers in the dimer, the equilibrium constant for the association 2M <==> M2 was determined as 0.8(+/-0.2) x 10(6) mol(-1)/I. The present choice of compounds was based merely on practical reasons. The model may be applied equally well to other similar cases.     

Dynamical dimer structure and liquid structure of fatty acids in their binary liquid mixture: decanoic/octadecanoic acid and decanoic/dodecanoic acid systems

Dimer structure and liquid structure of fatty acids in their binary mixtures such as decanoic acid (DA)/octadecanoic acid (SA) and DA/dodecanoic acid (LA) were studied through the measurements of self-diffusion coefficient (D), differential scanning calorimetry (DSC), density and viscosity. The obtained phase diagrams showed that DA and SA form a eutectic in the solid state but partly a solid solution in the SA-rich region; DA and LA form an incongruent-melting compound which forms a eutectic with DA. In the liquid mixture of DA and SA, the D of DA is larger than that of SA over the entire range of compositions and tends to approach the D of SA with increasing SA-mole fraction; the D of DA in the DA/LA system is also larger than that of LA especially in the LA-poor region and steeply approaches that of LA with increasing LA-mole fraction. These D values and phase diagrams were compared with those for the binary mixtures of n-alkanes (C14/C20, C19/C20 and C20/C24); it is concluded that the two kinds of fatty acids always form their individual homodimers in their liquid mixtures regardless of their compositions and temperatures.