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Biomedical subjects

M L Mello

Publications and source records attributed to M L Mello.

At least 55 records · Page 3Linked to original sources
PubMed1983

Basic fuchsins and the Schiff-aldehyde reaction. I. Spectral absorption characteristics in solution.

Spectral absorption profiles at the UV and visible ranges were detected spectrophotometrically for solutions of various basic fuchsins, for the SCHIFF reagent prepared from these stains and for the end product from SCHIFF-formaldehyde reaction. The aim was to detect whether absorption spectra could vary as a function of the basic fuchsin origin up to the point of being suspected of affecting potentially the spectrum of FEULGEN-stained chromatin. The results indicate a constancy in the spectral absorption characteristics for the absorption profiles at the visible range, when one considers SCHIFF reagents prepared from various basic fuchsins added with aldehyde. However, it is possible that size, stereoarrangement and electron distribution of the aldehyde- (eventually, ketone-) bearing molecule involved in SCHIFF-carbonyl reactions would function as auxochroms, the spectral characteristics of which could be affected by dye content and contaminants of the basic fuchsin.

Chemical Phenomena↗
PubMed1982

Induced metachromasia in bull spermatozoa.

The availability of sequential DNA phosphates to bind toluidine blue molecules after acid hydrolysis was studied in normally shaped and misshaped spermatozoa from subfertile and highly fertile bulls. The aim was to associate induced spermatozoal metachromasia with infertility. Some few normally and abnormally shaped cells from highly fertile bulls exhibited an induced metachromasia after being treated with 4 N HCl for 10-30 min at 25 degree C prior to staining. Subfertile bulls contained 12 times as many metachromatic spermatozoa as highly fertile animals. The induced toluidine blue metachromasia is suggested as a rapid and simple method for detecting bull spermatozoa bearing an anomalous DNA-protein complex. This nucleo-protein complex was found to be more frequent in subfertile bulls.

Animals↗
PubMed1982

Polarization microscopy and microspectrophotometry of Sirius Red, Picrosirius and Chlorantine Fast Red aggregates and of their complexes with collagen.

A detailed quantitative analysis of the anisotropic properties of Sirius Red F3B, Picrosirius, and Chlorantine Fast Red crystals, and of their complexes with a macromolecularly oriented protein either in a pure form or as part of a tissue structure was carried out. Collagen I was used as the protein model. Linear dichroism and dispersion of birefringence were investigated in dye aggregates, in stained filaments of collagen I and in collagen bundles in sections of tendon. A positive linear dichroism, the characteristics of which varied as a function of the dye type used, was demonstrated for the dye aggregates and stained substrates. However, even thin regions of the stained tendon collagen bundles showed very high absorbances, differing from the pattern reported previously for collagen stained with another sulphonated azo dye, Xylidine Ponceau. Consequently, not all these dyes enable protein concentration and orientation to be determined in collagen-containing structures. From the linear dichroism patterns it is assumed that the long axis of the molecules of these azo dyes is mostly parallel to that of filaments of pure collagen I and statistically parallel to the long axis of collagen bundles of tendon sections. The dye aggregates and, stained pure collagen I and tendon collagen bundles exhibited birefringent images with interference colours that varied as a function of thickness and packing state of the preparations, which is in agreement with reports in the literature. The optical retardations of the collagen bundles increased by a factor of 5-6 times after staining with Picrosirius. From data on form dichroism it is concluded that when studying the macromolecular orientation of collagen preparations stained with azo dyes, the choice of the mounting medium deserves consideration.

Azo Compounds↗
PubMed1981

Absorption spectrum of Feulgen-stained polytene chromosomes of Drosophila melanogaster.

Hetero- and euchromatic polytene chromosome regions of early and fully grown larvae of Drosophila melanogaster had their Feulgen absorption curves determined cytophotometrically. Hydrolysis conditions adequate to induce maximal DNA depurination were used. No differences in curve shapes specially concerning the absorption shoulder at the 520 less than or equal to lambda less than or equal to 550 nm spectral range were detected with advancing polytenization or when comparing the absorption patterns for the hetero- and euchromatic regions to each other. It is considered that prominence of the Feulgen absorption shoulder could be related to the amount of Schiff molecules di-substituted with apurinic acid aldehydes and to the relatively larger resistance of these apurinic acid fragments towards solubilization with acid hydrolysis due to their binding to nuclear proteins. It is therefore assumed that no significant differences owing to the above-cited factors exist for the chromosome regions analyzed at 2 phases of the polytenization process. Consequently, the replication of reiterated sequences from the main band DNA which occurs in polytene chromosome regions of Drosophila melanogaster appears not to affect the Feulgen absorption spectrum of this material.

Animals↗
PubMed1980

Acid lability of deoxyribonucleic acids of some polytene chromosome regions of Rhynchosciara americana.

An analysis of profiles of Feulgen hydrolysis curves has been carried out in two heterochromatic (B-15 and C-11) and one euchromatic (C-1) regions of polytene chromosomes of salivary glands of 66 day old Rhynchosciara americana larvae. Differences among these three regions have been found mostly concerning the period of predominant apurinic acid breakdown including the "lag" phase of teh apurinic acid depolymerization. The hydrolysis time for which maximal Feulgen-DNA values are attained also differs when comparing the hetero- and euchromatic regions of the C chromosome and the heterochromatic regions C11 and B15 to each other. Different labilities of DNA to acid hydrolysis have therefore been demonstrated for these chromosome regions. This has been tentatively correlated with differences in non-histone proteins some of which are assumed to be involved in chromatin compactness. Others (probably not concerned with chromatin compactness) are suggested to be associated with certain specific DNA types which are known to occur in these chromosome regions.

Animals↗
PubMed1980

Toluidine blue binding capacity of heterochromatin and euchromatin of Triatoma infestans Klug.

The localization of the absorption peaks of toluidine blue-stained heterochromatin (Ho and Hs) and euchromatin (Eo and Es) of the Malpighian tubules of the blood-sucking hemipteran, Triatoma infestans Klug was studied cytophotometrically (Ho and Eo: hetero- and euchromatin of nuclei with one single chromocenter; Hs and Es: hetero- and euchromatin of nuclei with several chromocenters). shifts of the absorption peaks to longer wave-lengths were found for the euchromatin fractions and Hs after RNAse treatment. The differences in the localization of absorption peaks after RNAse digestion when comparing the various chromatin types with one another are assumed to be due to differences in the number and proximity of DNA phosphates unattached to proteins and hence available to dye binding. The localization of the absorption peak of Ho at a relatively short wavelength (lambda = 570 nm) as compared with those for Hs, Eo, and Es, is attributed to a special state of chromatin condensation and practically absence of RNA in Ho. Also a certain removal of histones (probably, Hl) by the acetic ethanol "fixation" is speculated to play a role in the absorption curve properties of Ho subjected to TB staining.

Animals↗
PubMed1980

Feulgen-DNA absorption curves of polytene chromosome regions of Rhynchosciara americana.

Feulgen absorption spectra of polytene chromosome regions, differing in types of DNA composition and of chromatin compactness, were determined microspectrophotometrically in squashed salivary glands of Rhynchosciara americana. The absorption curves exhibited a secondary maximum at their ascending branch after the chromatins were maximally depurinated. The degree of shoulder prominence could not be specifically correlated with the packing state or even with richness in satellite repetitive DNA of the chromatins. It is assumed that other factors may exist which play a part in the phenomenon that gives rise to the Feulgen absorption shoulder characteristics. Differences in the extraction rate of the apurinic acid fragments due to their binding to specific non-histone proteins are suggested as contributing to the above-mentioned absorption patterns when comparing the various chromatin types.

Animals↗
PubMed1980

Anisotropic properties of the myelin sheath.

Form birefringence curves were determined for fixed (and unfixed rat axons before and after lipid extraction. The total detected birefringence was assumed to be due to the macromolecular array of myelin sheath components (phospholipids, cholesterol, and proteins). Unfixed nerves displayed negative form birefringence. Their form birefringence curve exhibited a = refractive index match point positioned at n = 1.46 (intrinsic birefringence). Formalin fixation induced decrease in the optical retardation values but did not affect the profile of the form birefringence curves. After lipid removal, however, the anisotropic patterns of the fixed and unfixed nerves changed. A positive form birefringence was then exhibited, which is attributed to the macromolecular orientation of the protein framework of the myelin sheath. Changes in the shape of the form birefringence curve and in the localization (and number) of the refractive index match point were found. They varied as lipids had been removed from nerves subjected or not to fixation. Therefore, the form birefringence of the myelin sheath proteins plays a part in the total phenomen observed in the whole nerves interfering with that displayed by phospholipids and cholesterol of the mentioned structure.

Animals↗
PubMed1979

Change with age of anisotropic properties of collagen bundles.

Form birefringence curves and linear dichroic properties of aging rat tendons are different from those of adult controls. The steepness of the form birefringence curves and the increased retardations found in aging tendons are ascribed to an increase in collagen aggregation accompanied by loss of tissue water. Based on increase of retardations due to intrinsic birefringence, a rise in crystallinity levels is suggested for the collagen bundles of aging tendons. The inversion of the dichroism signs and the change in the d11 (collagen fibers oriented parallel) and d1 (collagen fibers oriented perpendicular) spectral absorption profiles, mainly at the adsorption peaks for sections stained with toluidine blue solutions at pH 4.0 and 5.0, indicate modificiations at the acid glycosaminoglycan molecular orientation level with advancing age.

Achilles Tendon↗