Halobacterial megaplasmids are negatively supercoiled

Several covalently closed circular halobacterial megaplasmids (up to more than 500 kb) from different strains of Halolerax mediterranei, have been resolved by orthogonal-field alternating gel electro-phoresis (OFAGE). These molecules seem to be negatively supercoiled in vivo, as deduced from the effect of intercalating agents affecting their topology and, therefore, their electrophoretic mobility. It has also been demonstrated that the topolsomerase II Inhibitor novobiocin affects the native topological state of halobacterial megaplasmids impeding their migration in OFAGE under standard conditions for resolution of large supercoiled molecules.     

Continuous-flow NMR culture system for mammalian cells

A continuous-flow NMR culture system for mammalian cells has been developed on which ³¹P-NMR experiments under complete and strictly physiologic conditions have been performed. Observations on the response of the cellular metabolism to stresses such as starvation, low temperature and changes in environmental pH monitored by ³¹P-NMR are reported. The response of the intracellular pH relative to the external pH of the growth medium is studied. We find that under the experimental conditions used there exists a ΔpH varying between less than 0.2 and more than 0.6 pH units. These results are compatible with those obtained using other techniques.     

The economics of monocropping and intercropping by smallholders: The case of coconuts in Indonesia

This article contains a comparison of the profits of cultivating modern and traditional varieties of coconuts as a monocrop and as an intercrop, in ideal and in average growing conditions, with good and with average management. We carry out the analysis from a private (financial) and from a national (economic) perspective. The results show that intercropping generates more income than monocropping. In the conclusion we discuss why development organizations and Third World countries encourage monocropping.     

A new spectrophotometric assay for dopachrome tautomerase

The existence of a new enzyme involved in mammalian melanogenesis has been recently reported. The names dopachrome oxidoreductase and dopachrome tautomerase have been proposed for the enzyme. So far, this enzyme has been assayed at 475 nm on the basis of its ability to catalyze dopachrome decoloration. This method presents two major problems, derived from the instability of the substrate (dopachrome): (1) dopachrome must be prepared immediately before use, and (2) the rate of dopachrome decoloration in the absence of the enzyme is not negligible, and, furthermore, is enhanced by non-enzymatic agents. In order to overcome these problems, we present a new procedure that combines: (1) a quantitative, fast and easy way to prepare dopachrome from L-dopa by sodium periodate oxidation; (2) a spectrophotometric method in the UV region, at 308 nm, based on following the absorbance increase due to the enzyme-specific tautomerization of dopachrome to 5,6-dihydroxyindole-2-carboxylic acid as opposed to the absorbance decrease due to the spontaneous decarboxylative transformation of dopachrome into 5,6-dihydroxyindole. The advantages of these methods as compared to the previously used procedures are discussed.     

Coprecipitating IgG asymmetric antibodies: A possible role for Fab glycosylation,and speculations on their formation and functions in disease

IgG asymmetric antibodies are synthesized by the same cellular clones as the symmetric ones but appear in the immune response in different proportions. The evidence suggests that they are caused by asymmetric glycosylation on some IgG molecules in the Fab region. The cause of this is unknown but it could be speculated that there are cellular factors that induce glycosyl transferases or cause the molecule to be more accessible to glycosylation. The production of asymmetric antibodies can be modified by the physical status (soluble or particulate) of the antigen used as immunogen by the number and frequency of stimulation, and by physiological factors such as the ones secreted by the placenta and by lymphocytes that express progesterone receptors in response to hormone. An increase of these antibodies can be beneficial or harmful to the host, depending on the situation in which they act and the character of self or non-self of the antigens recognized. Editors note—Many of the ideas proposed in this article are very speculative, but it was thought appropriate to publish it in order to stimulate further discussion of the subject. It is an interesting role for Fab glycosylation that is proposed by Professor Margni. The ideas discussed are not necessarily those held by the Editorial Board or the reviewers, who felt that the evidence for many of the deductions made was very limited. It was also emphasized by the reviewers that the author's case would be substantially improved if more corroborative evidence was available from other groups. The Editors would welcome any comments on the subject for publication in future issues of the journal.     

Formaldehyde-induced appearance of septate junctions between digestive vacuoles

Tissue biopsies from (1) some chronic inflammatory diseases, (2) a necrotic tumoral process, (3) normal human lymphatic ganglia, and (4) two congenital diseases of the adrenal cortex were selected for study. A block from each biopsy was fixed in glutaraldehyde-paraformaldehyde; a second block was fixed in 10% formaldehyde. In all cases septate junctions between digestive vacuoles did occur in phagocytic cells and some adrenal cortex cells fixed in formaldehyde. These junctions were similar to those reported recently for malakoplakia phagocytes. Consistently, they were not found to attach organelles other than lysosomes derivatives. Both phagocytes and adrenal cortex cells in the material fixed in glutaraldehyde-paraformaldehyde did not display adhesive specializations between digestive vacuoles. This suggests that the septate junctions described herein are artifactuous structures induced by formaldehyde. There is, however, a certain degree of specificity of cells having the capability of developing these septate junctions. It is assumed that the coating material of digestive organelles in phogocytes and some other cells would be responsible for both cell specificity and organelle specificity of the formaldehyde-induced septate junctions.     

Regulation of the final phase of mammalian melanogenesis. The role of dopachrome tautomerase and the ratio between 5,6-dihydroxyindole-2-carboxylic acid and 5,6-dihydroxyindole.

The regulation of the final steps of the melanogenesis pathway, after L-2-carboxy-2,3-dihydroindole-5,6-quinone (dopachrome) formation, is studied. It is shown that both tyrosinase and dopachrome tautomerase are involved in the process. In vivo, it seems that tyrosinase is involved in the regulation of the amount of melanin formed, whereas dopachrome tautomerase is mainly involved in the size, structure and composition of melanin, by regulating to the incorporation of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) into the polymer. Moreover, using L-3,4-dihydroxyphenylalanine (dopa) and related compounds, it was shown that the presence of dopachrome tautomerase mediates an initial acceleration of melanogenesis since L-dopachrome is rapidly transformed to DHICA, but that melanin formation is inhibited because of the stability of this carboxylated indole compared to 5,6-dihydroxyindole (DHI), its decarboxylated counterpart obtained by spontaneous decarboxylation of L-dopachrome. Using L-dopa methyl ester as a precursor of melanogenesis, it is shown that this carboxylated indole does not polymerize in the absence of DHI, even in the presence of tyrosinase. However, it is incorporated into the polymer in the presence of both tyrosinase and DHI. Thus, this study suggests that DHI is essential for melanin formation, and the rate of polymerization depends on the ratio between DHICA and DHI in the medium. In the melanosome, this ratio should be regulated by the ratio between the activities of dopachrome tautomerase and tyrosinase.