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Biomedical subjects

G Diaz

Publications and source records attributed to G Diaz.

At least 19 recordsLinked to original sources
PubMed1992

Substitution of a single bacteriophage T3 residue in bacteriophage T7 RNA polymerase at position 748 results in a switch in promoter specificity.

The bacteriophage T3 and T7 RNA polymerases (RNAP) are closely related, yet exhibit high specificity for their own promoter sequences. In this work the primary determinant of T7 versus T3 promoter specificity has been localized to a single amino acid residue at position 748 in the T7 RNAP. Substitution of this residue (Asn) with the corresponding residue found in T3 RNAP (Asp) results in a switch in promoter specificity, and specifically alters recognition of the base pairs (bp) at positions -11 and, possibly, -10 in the promoter. A complementary mutation in T3 RNAP (T3-D749N) results in a similar switch in promoter preference for that enzyme. The hierarchy of bp preference by the mutant and wild-type enzymes for bp at -10 and -11, and the results of previous experiments, lead to a model for specificity in which it is proposed that N748 in T7 RNAP (and D749 in T3 RNAP) make specific hydrogen bonds with bases at -11 and -10 on the non-template strand in the major groove. The specificity determining region of T7 RNAP does not appear to exhibit homology to any known sequence-dependent DNA binding motif.

Amino Acid Sequence↗
PubMed1992

Stabilization of the N-terminal residues of luteinizing hormone-releasing hormone agonists and the effect on pharmacokinetics.

To stabilize leuprolide (1) against chymotrypsin and intestinal degradation several agonists of LHRH (2-12), modified at position 1, 2, or 3 and/or containing N-alpha-methyl at positions 1, 2, or 4, were synthesized by SPPS. These agonists were tested in vitro for (a) rat pituitary LHRH receptor binding, (b) LH release from rat pituitary cells, (c) stability against chymotrypsin, and (d) stability against rat intestinal degradation. The clearances of the compounds in the rat were determined using a RIA. Complete stabilization against chymotrypsin (t1/2) and lumenal degradation (T1/2) was achieved with substitution of NMe-Ser4 in leuprolide; however, with an increase in clearance. Substitution with 1-Nal3 increased both t1/2 and T1/2, while substitution with NAc-Sar1 increased only T1/2. [NAcSar1,NMeSer4,D-Trp6,Pro9NHEt]LHRH (12), the doubly stabilized analogue, was tested in the rat by both iv and id administrations, and its bioavailabilities were measured. No significant improvement in id absorption over leuprolide was observed.

Amino Acid Sequence↗
PubMed1992

Immunohistochemical study of synaptophysin distribution in the superior cervical ganglion of newborn and adult rats.

Intense synaptophysin immunoreactivity was observed around neuronal cell bodies and in the neuropil of the superior cervical ganglion of adult rats. In newborn rats synaptophysin was comparatively less concentrated and restricted to small interstitial spaces. In contrast, in newborns, consistent traces of positivity were found in the Golgi-like area of larger neurons, in agreement with the higher neonatal rate of synaptophysin synthesis. A few clusters of small neurons, numerically more expanded in adult rats, exhibited a dense reaction product filling the whole cytoplasm. No positivity was found in intraganglionic fibres.

Aging↗
PubMed1992

Collagen fibril ultrastructure alters after glycanolytic digestion.

Fixed fragments of bovine nasal septum cartilage were digested for six hours either with testicular hyaluronidase or streptomyces hyaluronidase or flavobacter chondroitinase ABC, and observed with a transmission electron microscope. Collagen fibril diameters (D) were measured to evaluate the effect of enzymatic digestion on the fibril size. This resulted in an increased frequency (17% to 47%) of "thin" fibrils (80 to 32 nm), followed by a decrease (65% to 31%) of the frequency of "mid" fibrils (32 to 64 nm). The frequency of "thick" fibrils (over 64 nm) showed a moderate increase (18% to 22%). Considering the relationship between fibril diameter, fibril volume and collagen content, the apparently relevant increase in number of the "thin" fibrils corresponds to an alteration of only 4% of the total collagen. On the other hand the increase of the "thick" fibrils implies a conspicuous alteration of 20% of the total collagen. The observed fibril rearrangement after digestion may be explained in terms of the wrap of matrix proteoglycans around each fibril. The enzymatic removal of the proteoglycans could make "mid" collagen fibrils free to regress into "thin" as well as to merge together into "thick" fibrils.

Animals↗
PubMed1991

Density profiles of biological specimens from Tiff files.

A program for achieving density profiles of Tiff images is described. Densitometric analysis is performed applying a cross-lateral averaging and longitudinal interpolation along the image axis. These procedures may be adapted to a variable axis curvature, length, width and morphological resolution. Since the Tiff format is supported by all desktop scanners and a large number of frame-grabbing devices, the range of applications includes the analysis of light and electron micrographs, autoradiograms, chromatograms, and data from any kind of bidimensional medium or flat surface. A special feature is the possibility of retrieving data from published pictures taken from literature.

Biology↗
PubMed1990

Substance P-like immunoreactivity in the human trigeminal ganglion.

Presence of substance P-like immunoreactive neurons and nerve fibers is demonstrated in the trigeminal ganglion of newborn and adult human subjects by the indirect immunofluorescence technique. Two populations of neurons containing high and low densities of immunoreactive material, respectively, are identified. Morphometric analyses indicate that (i) most of positive neurons are medium and small sized; (ii) immunoreactive perikarya grow in size from newborns to adults, with up to a 50% increase in diameter. Percent frequency of positive perikarya, on the other hand, is higher in newborns (23.6%) and decreases in adults (16.7%).

Aged↗
PubMed1990

Brain electrical field measurements unaffected by linked earlobes reference.

Recent theoretical analysis supports the possibility that using a linked earlobe reference in EEG studies might appreciatively distort the measured electrical field due to current flow over a low resistance path across the wire joining both ears. Such an effect would invalidate published quantitative EEG norms. Evidence for the balancing effect of this distortion was sought for in the EEG of 4 patients with well localized unilateral lesions, a situation in which this distortion would be most apparent. Statistical tests failed to reveal significant differences between EEGs recorded when ears were linked or unlinked. An analysis of the equivalent circuit reveals that a high skin/electrode impedance effectively makes the linked ear reference behave as an ordinary reference.

Brain↗
PubMed1990

Recognition of cell surface modulation by elliptic Fourier analysis.

A development of elliptic Fourier analysis, consisting in an alignment of harmonics according to their clockwise or counter-clockwise rotation, resolves the discrepancy between calculated harmonic frequencies and observed morphological periodicities. The new technique is supported by consistent data of empiric and fractal contours, comparatively analyzed and visualized with and without harmonic alignment. The method is particularly suitable for the recognition of periodic modulations of the cell surface. A preliminary analysis of two different cell populations (echinocytes and chondrocytes) shows distinct patterns of surface modulation that allow an effective discrimination of the cell type, while providing relevant information about the respective cytological configurations.

Algorithms↗
PubMed1990

[Diagnosis and treatment of myasthenia gravis: study of an inpatient population].

Between 1974 and 1987 we have examined 50 patients with the diagnosis of myasthenia gravis. Female preponderance (2.5: 1) was found. Also, it was observed that most of the patients were aged between 20 and 49 years. Beside the clinical examination, the following tests were performed: (1) edrofonium test, (2) supramaximal repetitive nerve stimulation, (3) serum acetylcholine antibodies titers and (4) intraperitoneal passive transference of patient's sera to mice and recording of meepp's amplitude in the phrenic-diaphragm preparation in vitro. These four tests gave positive values for myasthenia in 90 to 100% of the cases. Thymus radiological examination was carried out by pneumomediastinography, which proved to correlate with the histological picture of the gland, and computed tomography, which disclosed some discrepances with the histology. Treatment was based on anticholinesterase drugs, corticosteroids and thymectomy, being the corticosteroids the most valuable therapeutical tool. Nine patients treated with steroids disclosed transitory worsening of their signs and symptoms at very early stages after onset of corticosteroid therapy, 6 of them had a disfavorable course in their follow-up. This observation seem to have value in the early prognosis of the disease.

Adolescent↗
PubMed1990

Copper distribution within and between newborn livers.

Copper concentration was determined in different liver samples (blocks, needle biopsy and bile) obtained from 9 newborns and 3 infants at autopsy. Tissue blocks, sampled at ten equally spaced intervals between the left and the right lobe, revealed in newborns high copper concentrations, ranging from 93 to 335 mg/Kg of dry tissue with an upward trend from the right to the left lobe. The situation differed in infants where a lower and more evenly distributed copper content, ranging from 49 to 123 mg/Kg of dry tissue, was found, which seemed to approximate the situation found in adults. Copper concentration was generally high in bile, with an overall range from 99 to 413 mg/Kg of dry material. This fact was particularly significant in infants, considering their low hepatic copper content. Copper content determined in percutaneous biopts was significantly correlated to (P less than 0.01), though only moderately predictive of (r2 = 0.54), the average copper content calculated from the ten liver blocks.

Bile↗
PubMed1989

Elliptic fourier analysis of cell and nuclear shapes.

The elliptic Fourier analysis (EFA) is proposed to characterize the cell and nuclear shape. The principal feature of this method is that it decomposes shapes with a closed contour into subshapes each of which maintains a closed contour. A set of homogeneous, nonredundant descriptors, independent of the contour rotation and translation, is computed from the elliptic Fourier coefficients. These descriptors also account for the contour size and resolution. The paired analysis of the cell and nuclear shape provides an exhaustive and accurate definition of the nucleoplasmic configuration.

Computer Simulation↗