Abstract. 1. Sexuals of a leaf-cutting ant, Atta bisphaerica Forel, left their nest for nuptial flights in October to December. 2. When leaving a nest, 53 of the 479 winged sexuals (or alates) observed (11.1%) carried up to three inquiline spiders of Attacobius luederwaldti . 3. Spiders exclusively selected winged sexuals, not workers, and preferred females, indicating their expectation of the stronger flight ability of females. Neither these sexuals nor workers that appeared out of the nest on flight days attempted to remove or attack spiders on the body of alates. 4. New qucens landing from their nuptial flight did not carry spiders, indicating that the spiders had left the ants in the sky to be dispersed by wind. 5. No spiders were found in more than 100 incipient nests, which were estimated to be 2–3 months old. This suggests that the spiders jumped off the alate during mid-flight and dispersed on the wind to inhabit larger nests. 相似文献
Two lowMr phosphotyrosine protein phosphatases have been isolated from rat liver. The enzymes were previously known as lowMr acid phosphatases, but several recent studies have demonstrated that this family of enzymes possesses specific phosphotyrosine protein phosphatase activity. We determined the complete amino acid sequences of the two isoenzymes and named them AcP1 and AcP2. Both consist of 157 amino acid residues, are acetylated at the NH2-terminus, and have His as the COOH-terminus. The molecular weights calculated from the sequences are 18,062 for AcP1 and 17,848 for AcP2. They are homologous except in the 40–73 zone, where about 50% of residues are different. This fact suggests that the two isoenzymes are produced by an alternative splicing mechanism. There is no homology between these two isoenzymes and the receptor-like phosphotyrosine protein phosphatases LAR, CD45, human placenta PTPase 1B, and rat brain PTPase-1. AcP1 and AcP2 are also distinct from rat liver PTPase-1 and PTPase-2, since these last enzymes have higher molecular weights. AcP1 differs from AcP2 with respect to (1) substrate affinity and (2) its sensitivity to activators and inhibitors, thus suggesting a their different physiological function. 相似文献
The 2:1 adriamycin-Fe(III) complex is able to bind to DNA and to catalyze its oxidative destruction. The binding of the drug-metal complex to DNA is indicated by characteristic spectral changes which are different from those seen with adriamycin intercalation and by the propensity of the drug-metal complex to precipitate DNA. Furthermore, intercalated adriamycin appears not to be available for iron binding. The resulting ternary complex is quite stable: it is not disrupted by incubation in the presence of EDTA and can be isolated by using Sephadex G-50 column chromatography. Disruption of the ternary complex requires vigorous conditions (extraction with phenol at 60 degrees C). The adriamycin-iron complex in free solution has the capacity to catalyze the reduction of oxygen by thiols. The DNA-bound drug-metal complex preserves this capacity over a wide range of complex/DNA ratios. As a consequence of this thiol-dependent oxygen reduction, DNA is cleaved. This thiol-dependent DNA cleavage has been shown to require hydrogen peroxide as an intermediate product. These results have led us to propose that the thiol-dependent DNA cleavage reaction has two stages involving (1) reduction of oxygen leading to hydrogen peroxide and then (2) peroxide-dependent DNA cleavage. An unusual property of this reaction is that the cleavage is not random but gives rise to a defined 2300 base pair fragment. 相似文献
Activity levels of 7-ethoxycoumarin O-deethylase (ED), aminopyrine N-demethylase (APD), p-nitroanisoleO-demethylase (p-NAD) and glucose-6-phosphate dehydrogenase (G-6-PDH) were determined in incubation mixtures for the liver-microsomal assay (LMA) at time 0 and after 1 and 2 h incubation under conditions for mutagenic assay. The experiments were performed with S9 liver fractions from mice (induced with Na-phenobarbital and β-naphthoflavone) and rats (induced with Aroclor 1254) with and without G-6-PDH in the incubation mixtures.
In the absence of G-6-PDH the activities were significantly lower at time 0 in the mouse. The pattern of stability, however, was similar for the activities, with an increase of stability after 1 and 2 h of pre-incubation (an exception for p-NAD).
Only ED activity showed a similar behaviour in the rat. No differences were present for APD and p-NAD activities at time 0 in the rat, but the enzyme stabilities were significantly decreased after 2 h of incubation (about 15% and 10% for APD and p-NAD respectively) in the absence of G-6-PDH.
At time 0, the amounts of G-6-PDH differed between mouse and rat fractions; however, during the incubations for LMA they decreased by about 57% and 53% for the two species, respectively. In addition to the above biochemical results, the presence of exogenous G-6-PDH in the incubations for the mutagenic assay, significantly increased the mitotic gene conversion and mitotic crossing-over of dimethylnitrosamine (DMN) and AR2MNFN (a nitroimidazo[2,1-b]thiazole) in the D7 strain of Saccharomyces cerevisiae. 相似文献
The possible linkage between a gene causing heterocellular hereditary persistence of fetal hemoglobin (HPFH) and human non-alpha globin loci has been studied in a large Sardinian family. In this family a homozygous beta o-thalassemic patient was found, with an unusually mild form of this disease, which was ascribed to the co-existence of a gene causing heterocellular HPFH. DNA polymorphisms in the non-alpha globin cluster were analyzed by restriction enzyme digestion with HincII, HindIII and BamHI and with epsilon-, gamma-and beta-globin probes; the pattern of inheritance of these polymorphisms indicates that the HPFH gene is transmitted with one beta o-thalassemic gene in a single instance, with the second beta o-thalassemic gene in three instances and with a normal beta-globin gene in two cases. These data indicate that this HPFH gene is not linked to the non-alpha globin gene cluster, in contrast to previous observations with different HPFH genes, and suggest that this gene might code for diffusible substances acting, directly or indirectly, on gamma-globin gene expression. 相似文献
Adriamycin, a new antitumour antibiotic of the anthracycline group with a structural formula very similar to daunorubicin, has proved to have potent tumour-growth-inhibiting properties, and to be particularly effective in childhood malignancies. Though adriamycin produces a higher percentage of side-effects than daunorubicin—namely, stomatitis and alopecia—a lower dosage may be used for therapy. 相似文献
Abstract A protocol for efficient electrotransformation of Streptococcus agalactiae (group B streptococcus) Lancefield's strain O90R (NTCT 9993) (an unencapsulated derivative of type Ia strain O90) was developed. The Escherichia coli - Streptococcus shuttle vector pDP28 (7.8 kb) carrying the ermB gene for resistance to erythromycin was used as donor DNA. Frozen 'electrocompetent' cells were prepared by repeated washes in 10% glycerol. A 50-μl aliquot containing about 5×109 colony forming units of bacteria was subjected to the electric pulse. Optimal conditions for electrotransformation were determined using different media, harvesting cells at different points of the growth curve, and using different field strengths. The dose-response curve for transformation of S. agalactiae with pDP28 showed one-hit kinetics as donor DNA varied between 0.01 and 3 μg. The efficiency of electrotransformation for this range of amounts of donor DNA was 1.2×104 cfu μg−1. The transformation frequencies obtained with this electroporation protocol are high enough to allow both subcloning and shotgun cloning of streptococcal DNA in S. agalactiae . 相似文献
Ascorbate is oxidized to the free radical monodehydroascorbate by O2.- and by H2O2 (through the action of ascorbate peroxidase) formed in the Mehler reaction by isolated spinach (Spinacia oleracea) thylakoids. Light-dependent electron transport from water to monodehydroascorbate is shown to be coupled to ATP formation with a ratio ATP:O2 of 2. In the presence of ascorbate the net O2 exchange balance of the Mehler reaction is close to zero, and the synthesis of ATP is increased 2 to 3 times due to the extra electron transport to the monodehydroascorbate free radical. A scheme of the electron transport in the presence of ascorbate is discussed. 相似文献