Comparison of the solution and crystal conformations of (G + C)-rich fragments of DNA.

DNA fragments crystallize in an unpredictable manner, and relationships between their crystal and solution conformations still are not known. We have studied, using circular dichroism spectroscopy, solution conformations of (G + C)-rich DNA fragments, the crystal structures of which were solved in the laboratory of one of the present authors. In aqueous trifluorethanol (TFE) solutions, all of the examined oligonucleotides adopted the same type of double helix as in the crystal. Specifically, the dodecamer d(CCCCCGCGGGGG) crystalized as A-DNA and isomerized into A-DNA at high TFE concentrations. On the other hand, the hexamer d(CCGCGG) crystallized in Z-form containing tilted base pairs, and high TFE concentrations cooperatively transformed it into the same Z-form as adopted by the RNA hexamer r(CGCGCG), although d(CCGCGG) could isomerize into Z-DNA in the NaCl + NiCl2) aqueous solution. The fragments crystallizing as B-DNA remained B-DNA, regardless of the solution conditions, unless they denatured or aggregated. Effects on the oligonucleotide conformation of 2-methyl-2,4-pentanediol and other crystallization agents were also studied. 2-Methyl-2,4-pentanediol induced the same conformational transitions as TFE but, in addition, caused an oligonucleotide condensation that was also promoted by the other crystallization agents. The present results indicate that the crystal double helices of DNA are stable in aqueous TFE rather than aqueous solution.     

Mixing power, external convection, and effectiveness in bioreactors

The phenomena of mixing and mass transfer of substrates to microorganisms greatly affect the biochemical reactions which take place in fermentation processes. The effect that agitation power has on the observable reaction kinetics involved in beer fermentation has been studied in different types of bioreactors, from laboratory to industrial scale. With this aim in mind, an effectiveness factor, eta, is introduced which is defined as the relation between the existing rate of reaction, whichever bioreactor is considered, and the reaction rate in the well-mixed, and therefore presumably homogeneous, bioreactor with no diffusional limits. The limitation to homogeneously supplying nutrient material to the cells produces a decrease in this effectiveness factor, which has been correlated to the energy dissipation rate with a similar slope to that which appears in an existing correlation in the literature between this energy and the mass transfer coefficient. Additionally, a dimensionless reaction-convection number, N(RC), which is a function of the power input per unit volume, is proposed, which has been appropriately employed in correlating the effectiveness factor for the types of processes in which convection may be the key resistance factor. (c) 1996 John Wiley & Sons, Inc.     

An extended x-ray absorption fine structure study of the high-affinity cation-binding site in the purple membrane.

The structure of the high-affinity cation-binding site of bacteriorhodopsin was studied using extended x-ray absorption fine structure techniques. The results obtained for Mn2+ in aqueous solution and for the complex BR-Mn2+ (1:1 molar ratio) show great similarities, suggesting that Mn2+, when bound to this site, is coordinated with six atoms of oxygen, forming an octahedral disposition. The interatomic distance between the atoms of oxygen and the Mn2+ was found to be 2.17 A for the complex BR-Mn2+, similar to Mn2+ in solution (2.15 A). In addition, the absence of any other peak at greater distances in the Fourier-transformed spectrum indicates that neither phosphorus nor sulphur atoms are present in the second coordination shell. This suggests that this binding site is located in the protein, discarding the proximity of lipid polar headgroups.     

Oxidation and amidation of salicylate by Streptomyces species

Seven streptomycete strains were tested for biotransformation of salicylate. The products were identified by nuclear magnetic resonance spectroscopy and three types of conversion were found. Streptomyces cinnamonensis and Streptomyces spectabilis formed gentisate and salicylamide concurrently. Streptomyces rimosus transformed salicylate to salicylamide. Streptomyces lividans, Streptomyces coelicolor, Streptomyces griseus and Streptomyces avermitilis produced only gentisate. Time course studies of salicylate conversion by thin-layer chromatography and high pressure liquid chromatography showed that salicylamide was accumulated in the culture broth, whereas gentisate was further metabolized.Key words: salicylate, gentisate, salicylamide, biotransformation, Streptomyces spp.     

A new species of Lupinus (Fabaceae: Lupininae) from southeastern Brazil

Lupinus rubriflorus Planchuelo, from Rio Grande do Sul, Brazil, is described and illustrated. This species is related toL. bracteolaris s.l. differing in pubescence, stipules, and floral characters.     

Relationship between the levels of wheat-rye metaphase I chromosomal pairing and recombination revealed by GISH

The metaphase I and anaphase I stages of meiosis of wheat×rye hybrids carrying the ph1b mutation were analyzed by genomic in situ hybridization. This technique allows distinction between three different types of wheat-rye associations in metaphase I configurations as well as detection of wheat-rye recombinant chromosomes in anaphase I cells. The frequency of associations between wheat and rye chromosomes greatly exceeded the level of wheat-rye recombination found in the three hybrids examined. Extremely distal associations, which account for about 50% of the total wheat-rye metaphase I chromosomal pairing, can explain such a discrepancy between metaphase I and anaphase I data. It is further discussed whether these associations reflect very distally located chiasmata or nonchiasmatic pairing. The sizes of the segments exchanged in wheat-rye recombinant chromosomes provide cytological evidence that wheat-rye recombination is restricted to the distal chromosomal regions. Received: 24 August 1995; in revised form: 27 February 1996 / Accepted: 28 March 1996     

A comparative study of the purity, enzyme activity, and inactivation by hydrogen peroxide of commercially available horseradish peroxidase isoenzymes A and C

Horseradish peroxidase (HRP) is a commercially important enzyme that is available from a number of supply houses in a variety of grades of purity and isoenzymic combinations. The present article describes a comparative study made on nine HRP preparations. Six of these samples were predominantly composed of basic HRP, pl 8.5, and three of acidic HRP, pl 3.5. Two of the basic preparations were of lower purity than the others. The apparent molar catalytic activity of basic HRP with 0.5 mMABTS and 0.2 mM H(2)O(2) was around 950 s(-1) (about 770 s(-1) for the less pure samples) and with a 5 mM guaiacol and 0.6 mM H(2)O(2) was about 180 s(-1) for all the samples. A similar value (approximately 1000 s(-1)) was observed for acidic HRP but only at higher concentrations of ABTS (20 mM). With 20 mM guaiacol the molar catalytic activity of the acid isoenzyme was 65 s(-1). The apparent K(M) for ABTS of the acidic isoenzyme was 4 mM whereas for the basic isoenzyme it was 0.1 mM. All the enzymes were inactivated by H(2)O(2) when it was supplied as the only substrate. Under these conditions the partition ratio (r = number of catalytic cycles given by the enzyme before its inactivation), apparent dissociation constant (K(l)), and apparent rate constant of inactivation (k(inact)) were about twice as large for the acidic samples (1350, 2.6 mM, 9 . 10(-3) s(-1)) as for the basic (650, 1.3 mM, 5 . 10(-3) s(-1)). The apparent catalytic constant (k(cat)) was 3-4 times larger, and the efficiency of catalysis (k(cat)/K(l)) was double for the acidic isoenzyme, but the efficiency of inactivation (k(inact)/K(l)) was similar. The data obtained provide useful information for those using HRP isoenzymes for biotechnological applications (e.g., biosensors, bioreactors, or assays). (c) 1996 John Wiley & Sons, Inc.     

Keratella distribution in North Patagonian lakes (Argentina)

The distribution of Keratella species from 15 different lakes in North Patagonia (Argentina) was analysed. The genus was not present at altitudes above 1000 m. K. tropica was restricted to Patagonian Plateau lakes with a comparatively high conductivity. A morphometric analysis of the widely distributed K. cochlearis was performed. Results showed three groups of K. cochlearis corresponding to Andean lakes, Patagonian Plateau lakes and a Patagonian Reservoir.     

The Gene Encoding the Catalytic Subunit Cα of cAMP-Dependent Protein Kinase (Locus PRKACA) Localizes to Human Chromosome Region 19p13.1

We have determined the chromosomal localization of the gene for the catalytic subunit Cα of cAMP-dependent protein kinase (locus PRKACA) to human chromosome 19 using polymerase chain reaction (PCR) and Southern blot analysis of two different somatic cell hybrid mapping panels. In addition, PCR analysis of a chromosome 19 mapping panel revealed the presence of a human Cα-specific amplification product only in cell lines containing the region 19p13.1 to 19q12. Finally, two-color fluorescencein situhybridization to metaphase chromosomes using the human Cα cDNA and human chromosome 19 inter-Alu-PCR product as probes localized the human Cα gene to chromosome region 19p13.1.     

Twenty-Four-Hour Variations in the Sensitivity of Rat Aorta to Vasoactive Agents

The presence of time-dependent variations in the in vitro sensitivity of aorta preparations to either vasoconstricting or relaxing agents was investigated in rats maintained in light from 08: 00 to 20: 00 and in darkness from 20: 00 to 08: 00. Rat thoracic aorta rings were obtained from animals sacrificed at four different times of the day. The rat aorta was found to be more sensitive to the constricting effect of phenylephrine at 15: 00, and of 5-hydroxytryptamine at 21: 00. On the other hand, both endothelium-dependent and -independent relaxations were more remarkable at 03: 00 than at other times of the day. These variations represented significant circadian rhythms when analyzed by analysis of variance. Different in vitro responsiveness to these agents might reflect changes in the sensitivity and/or number of related receptors in vascular preparations. In conclusion, the circadian time of animal sacrifice to obtain vascular preparations constitutes an important aspect of the research method and a key determinant of findings. (Chronobiology International, 13(6), 465-475, 1996)