Cessation of reentry of simian virus 40 DNA into replication and its simultaneous appearance in nucleoprotein complexes of the maturation pathway.

Newly synthesized SV40 DNA is used as a template for further DNA synthesis (reenters replication) or as a substrate in the assembly of virions (maturation pathway). The time courses of reentry into replication and progression along the maturation pathway were both determined on identical samples. DNA, synthesized during a 20-min pulse, reentered replication over a period of several hours and then was removed from the pool of molecules available for replication. The cessation of reentry coincided with the maturation of this DNA from the chromatin form to previrion and virion forms. More reentry and less maturation was observed at 24 h postinfection than at 42 h postinfection. The data are consistent with the hypothesis that the factor(s) responsible for cessation of reentry is also responsible for initiation of the maturation pathway.     

Tetracyclic triterpenes. Part VI [1] . The synthesis of 4,4,14α-Trimethyl-19 ( 10 → 9β) abeo-steroids. Synthons for the preparation of cucurbitacins

The effective synthesis of 4,4,14α-trimethyl-19 (10 → 9β) abeo-steroids (iv), (v), and (Vl) with two- and five-carbon side chains from lanosterol is described. Their structures were proved on the basis of spectral data. The title compounds are the first synthetic synthons for the preparation of 4,4,14α-trimethyl-steroids with an unnatural configuration.     

Dehydrodieugenols from Ocotea cymbarum

The trunk wood of Ocotea cymbarum from the Amazon basin contains α-phellandrene, α-pinene, eugenol, dehydrodieugenol and its monomethyl ether, as well as the previously unknown dehydrodieugenol-B (4,5′-diallyl-2′-hydroxy-2,3′-dimethoxydiphenyl ether).     

Regulation of Ca2+ efflux from kidney and liver mitochondria by unsaturated fatty acids and Na+ ions.

The effects of fatty acids and monovalent cations on the Ca2+ efflux from isolated liver and kidney mitochondria were investigated by means of electrode techniques. It was shown that unsaturated fatty acids and saturated fatty acids of medium chain length (C12 and C14) induced a Ca2+ efflux from mitochondria which was not inhibited by ruthenium red, but was specifically inhibited by Na+ and Li+. The Ca2+-releasing activity of unsaturated fatty acids did not correlate with their uncoupling activity. In kidney mitochondria a spontaneous, temperature-dependent Ca2+ efflux was observed which was inhibited either by albumin or by Na+. It is suggested that the net Ca2+ accumulation by mitochondria depends on the operation of independent pump and leak pathways. The pump is driven by the membrane potential and can be inhibited by ruthenium red, the leak depends on the presence of unsaturated fatty acids and is inhibited by Na+ and Li+. It is suggested that the unsaturated fatty acids produced by mitochondrial phospholipase A2 can be essential in the regulation of the Ca2+ retention in and the Ca2+ release from the mitochondria.     

Stereological investigation on the increase in surface area due to the microtriches of the hydatid cyst in different organs and in different hosts

Bortoletti G. and Diaz G. 1978. Stereological investigation on the increase in surface area due to the microtriches of the hydatid cyst in different organs and in different hosts. International Journal for Parasitology8: 433–436. The increase in surface area of the germinal membrane due to the microtriches has been morphometrically investigated in Echinococcus granulosus cysts developed in three different intermediate hosts. The results, achieved by Stereological methods, indicate that the development of the microtriches: (a) is more or less homogeneous all over the germinal membrane of the cysts; (b) is greater in human than in pig and sheep cysts; (c) is also greater in lung than in liver cysts within the same host and it is not related to the fertility or sterility of the parasite.     

LONG-TERM DEVELOPMENTAL CHANGES IN XANTHIUM INDUCED BY GIBBERELLIC ACID

One application of gibberellic acid (GA₃) to Xanthium shoots resulted in an initial large stimulation, followed by inhibition, of internode elongation. After presumed translocation of the hormone from the locus of its application to the stem apex several morphological changes were observed. There was a significant increase in number of mitotic figures in the apical meristem and a twofold increase in volume of the apical dome. With time, the rate of leaf production was accelerated about 1.8 times. The phyllotaxis of leaf primordia initiated under the influence of GA:, changed from a (2, 3) contact parastichy pattern in control shoot to a (3, 5) pattern. Final petiole length was smaller than the control, and the absolute rate of lamina expansion decreased under prolonged treatment. Gibberellic acid had a pronounced effect on leaf morphology. GA_a induced the development of lanceolate leaves instead of typical deltoid leaves. The reduction in leaf area coincided with a 32% reduction in the average area of epidermal cells. Plastochron changes were correlated with anatomical and morphological changes during the course of leaf development.     

Voltage-dependent conductance induced by hemocyanin in black lipid films

When hemocyanin is added to a black lipid film, the conductance increases in discrete steps. For negative potentials the single step conductance is constant, but for positive potentials the step conductance appears to decrease as the potential increases. At high positive potentials the conductance fluctuates between several levels. These data suggest that, in lipid membranes, hemocyanin conducts ions through discrete channels. The voltage-dependent conductance observed at high levels of conductance seems to be a consequence of the properties of the conductance of the single channel.     

Steroid-receptor quantitation and characterization by electrophoresis in highly cross-linked polyacrylamide gels.

Conditions for discontinuous polyacrylamide gel electrophoresis have been defined in which progesterone receptors of chick oviduct cytosol and a variety of steroid-binding proteins from other sources are stable and amenable to quantitative analysis. The essential modifications from standard procedures include the use of (1) separation gels in which the cross-linking agent/acrylamide monomer = 15:85, (2) glycerol (10% v/v) in all phases of the Trisglycine-HCl buffer system (pH 10.2 in the separation phase during electrophoresis at 0 degrees), and (3) a layer of a charged reducing agent, thioglycolate, beneath the sample layer. Electrophoresis of untreated oviduct cytosol labeled with [3H]progesterone +/- competing steroids revealed a heterodisperse slow peak and a sharp fast peak. Both peaks displayed the steroid-binding specificity and saturability that are characteristic of intracellular receptors. Recovery of steroid from both the slow and fast components increased linearly with sample load up to 60 mul of cytosol (1.2 mg of protein)/gel (6 mm diameter). The specific progesterone binding detected by this technique was comparable to that detected by charcoal-dextran treatment or ion exchange filtration. Relative electrophoretic mobilities (Rf) of globular protein standards and steroid-protein complexes in cytosol and chick serum were measured in separation gels with total gel concentrations (T) systematically varied from 5 to 15% (w/v). Data were processed by computer programs to obtain weighted linear regressions of log Rf on T (Ferguson plots) and the joint 95% confidence limits of the slopes (-KR) and intercepts of these plots. Molecular radii (R) of the binding components and apparent molecular weights (M) were calculated from the linear correlation of R with KR 1/2 for the standards. The value of M is approximately 158,000 obtained for the cytosol fast component was independent of the length of the separation gel, the presence of a stacking gel or prior exposure of the cytosol to KCl. It was higher than expected from the sedimentation coefficient of 4.2 S in the same pH 10.2 buffer. Electrophoresis in 170-mm separation gels without stacking gels revealed that KCl extracts of protamine-precipitated cytosol contain a different receptor form, of lower net negative charge than the cytosol fast form. The results demonstrate the utility of electrophoresis in highly cross-linked gels of several concentrations to discriminate between various receptor forms and steroid-binding components of serum. This method may lead to overestimates of M for highly asymmetric receptor forms.