Modulation of transient type K channel cloned from rat heart.

We have cloned a transient type K channel from rat heart (RH10) and coexpressed a metabotropic glutamate receptor (mGluR5) to study the functional modulation of RH10 coupled to the phosphatidylinositol (PI) hydrolysis. Stimulation of mGluR5 suppressed peak amplitude of RH10 current and affected voltage dependence of activation and inactivation of the channel.     

Effect of coenzymes on the quaternary structure conformation of glyceraldehyde-3-phosphate dehydrogenases of mung beans and rabbit muscle.

Kinetics of thermal inactivation of glyceraldehyde-3-phosphate dehydrogenases of mung beans and rabbit muscle have been studied under different pH conditions in the absence and presence of various concentrations of NAD+ and NADH. The data have been discussed with respect to the effect of the coenzymes on the quaternary structure symmetry of the two enzymes and their binding isotherms. Both the (homo-tetrameric) apo-enzymes exhibit biphasic kinetics of thermal inactivation, characteristic of C2 symmetry, at lower pH values and a single exponential decay of enzyme activity, characteristic of D2 symmetry, at higher pHs. In each case, NAD+ has no effect on the biphasic kinetic pattern of thermal inactivation at lower pH values, but NADH brings about a change to single exponential decay. At higher pH values, NADH does not affect the kinetic pattern (single exponential decay) of any enzyme, but NAD+ alters it to biphasic kinetics in each case. The data suggest that NAD+ and NADH have higher affinity for the C2 and D2 symmetry conformation, respectively. With mung beans enzyme, the effect of NAD+ on the two rate constants of biphasic inactivation at pH 7.3 is consistent with a Kdiss equal to 110 microM. The NAD(+)-dependent changes in the kinetic pattern of thermal inactivation of this enzyme at pH 8.6 suggest a positive cooperativity in the coenzyme binding (nH = 3.0). In the binding of NADH to the mung beans enzyme, a weak positive cooperativity is observed at pH 7.3.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bivariate flow cytometry of farm animal chromosomes: a potential tool for gene mapping

Bivariate flow karyotypes of chromosomes from sheep, cattle and pig lymphocytes and from a cattle-mouse somatic cell hybrid line were obtained using a dual laser fluorescence-activated cell sorter (FACS). Pig chromosomes were resolved into 19-20 peaks, indicating that most, if not all, pig chromosomes could be separated by this technique. Sheep chromosomes showed incomplete separation but three clear peaks, presumably representing the three large metacentric chromosomes, plus five other clusters were obtained. Cattle chromosomes showed poor separation but about four peaks could be distinguished, indicating that certain chromosomes could be sorted in this species. The use of cattle-mouse hybrids may enable other individual cattle chromosomes to be obtained. It is concluded that FACS separation will be a useful additional tool for gene mapping.     

Facile and stereoselective synthesis of 2'-5'-oligothioadenylate by UO2(2+) ion catalyst.

The synthesis and characterization of 2'-5'-oligothioadenylate by UO2(2+) ion catalyst are described. The polymerization of imidazole-activated thioadenylate or thioinosylate yielded oligomers containing mainly 2'-5'-internucleotidyl blond and Rp configuration at phosphorous atom.     

Life history patterns of river invertebrates

The initiation of invertebrate distribution patterns in rivers occurs by choice of oviposition sites and is influenced by the evolved reproductive strategies of the individual species. Subsequent redistribution by migration or drifting establishes patterns which are then modified by environmental influences on growth and mortality. Continuity of life cycles is sustained by variations on a number of defined life history strategies combined with evolved behavioural responses.     

Phytoplankton and physical-chemical features of Tavropos Reservoir,Greece

Phytoplankton biomass values in Tavropos Reservoir, ranging from 92 to 1071 mg m^–3, are within a range characteristic of oligotrophic waters. The seasonal sequence of biomass shows three annual peaks, differing from the monoacmic pattern seen in oligotrophic lakes. This sequence was profoundly affected by changes in water withdrawal and inflow rates. Diatoms, cryptophytes, chrysophytes and dinoflagellates, in that order, were the major constituents of the reservoir phytoplankton. The succession, from diatoms and chrysophytes in late winter-spring, to centric diatoms in late spring-summer and again to diatom-chrysophytes in late autumn was similar to that in oligotrophic lakes.     

Primary sequence and functional expression of a novel ouabain-resistant Na,K-ATPase. The beta subunit modulates potassium activation of the Na,K-pump.

In order to understand the molecular mechanism of ouabain resistance in the toad Bufo marinus, Na,K-ATPase alpha and beta subunits have been cloned and their functional properties tested in the Xenopus laevis oocyte expression system. According to sequence comparison between species, alpha 1, beta 1, and beta 3 isoforms were identified in a clonal toad urinary bladder cell line (TBM 18-23). The sequence of the alpha 1 isoform is characterized by two positively charged amino acids (Arg, Lys) at the N-terminal border of the H1-H2 extracellular loop and no charged amino acid at the C terminus, a pattern distinct from the ouabain-resistant rat alpha 1 isoform. The coexpression of alpha 1 beta 1 or alpha 1 beta 3 TBM subunits in the Xenopus oocyte resulted in the expression of identical maximum Na,K-pump currents with identical inhibition constant for ouabain (Ki) (alpha 1 beta 1: 53 +/- 3 microM; n = 7 vs. alpha 1 beta 3: 57 +/- 3.0 microM; n = 8) but distinct potassium half activation constant (K1/2) (alpha 1 beta 1: 0.87 +/- 0.08 mM, n = 16; alpha 1 beta 3: 1.29 +/- 0.07 mM, n = 17; p less than 0.005). We conclude that (i) the TBM alpha 1 isoform is necessary and sufficient to confer the ouabain resistant phenotype; (ii) the beta 3 or beta 1 subunit can associate with the alpha 1 equally well without affecting the ouabain-resistant phenotype; (iii) some specific sequence of the beta subunit can modulate the activation of the Na,K-pump by extracellular potassium ions.     

Use of structure-directed DNA ligands to probe the binding of recA protein to narrow and wide grooves of DNA and on its ability to promote homologous pairing.

We have used circular dichroism and structure-directed drugs to identify the role of structural features, wide and narrow grooves in particular, required for the cooperative polymerization, recognition of homologous sequences, and the formation of joint molecules promoted by recA protein. The path of cooperative polymerization of recA protein was deduced by its ability to cause quantitative displacement of distamycin from the narrow groove of duplex DNA. By contrast, methyl green bound to the wide groove was retained by the nucleoprotein filaments comprised of recA protein-DNA. Further, the mode of binding of these ligands and recA protein to DNA was confirmed by DNaseI digestion. More importantly, the formation of joint molecules was prevented by distamycin in the narrow groove while methyl green in the wide groove had no adverse effect. Intriguingly, distamycin interfered with the production of coaggregates between nucleoprotein filaments of recA protein-M13 ssDNA and naked linear M13 duplex DNA, but not with linear phi X174 duplex DNA. Thus, these data, in conjunction with molecular modeling, suggest that the narrow grooves of duplex DNA provide the fundamental framework required for the cooperative polymerization of recA protein and alignment of homologous sequences. These findings and their significance are discussed in relation to models of homologous pairing between two intertwined DNA molecules.