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Biomedical subjects

M Simon

Publications and source records attributed to M Simon.

At least 613 records · Page 34Linked to original sources
PubMed1980

Phase variation: evolution of a controlling element.

Phase variation in bacteria is regulated by homologous recombination at a specific DNA site. This recombinational event causes the inversion of a 970-base-pair DNA sequence that includes the promoter necessary for transcription of a flagellar gene. The invertible segment is flanked by two sites that are necessary for the inversion and contains a gene (hin) whose product mediates the inversion event. The hin gene shows extensive homology with the TnpR gene carried on the Tn3 transposon. It is also homologous with the gin gene carried on bacteriophage mu. These relationships suggest that the phase variation system may have evolved by the association of a transposon with a resident gene and the subsequent specialization of these elements to regulate flagellar antigen expression.

Amino Acid Sequence↗
PubMed1980

17-Hydroxycorticosteroids in urine.

A new method has been devised to extract 17-hydroxycorticosteroids (17OH-CS) from a hydrolyzed urine using an EXTUBE fiber column. This extraction was combined with a modified Porter-Silber color reaction to quantitate total urinary 17OH-CS. The new method takes only half the time required in older methods. Recovery of tetrahydrocortisone in the new method was improved to 85--95% compared with 70% in the previous method. Between-run precision (C.V.%) was concentration dependent in both methods and was improved to 5--7% compared with 10--18% in the previous method. Evidence was obtained to demonstrate that the new methodology would provide the same information and interpretation as the older, more cumbersome method.

17-Hydroxycorticosteroids↗
PubMed1980

Binding of insulin to bovine liver plasma membrane. Use of insulin analogues modified at the A1 residue.

Bovine liver plasma membranes [Rösen, Ehrich, Junger, Bubenzer & Kühn (1979) Biochim. Biophys. Acta587, 593-605] show similar insulin-binding characteristics, as evaluated by Scatchard analysis, to those of membrane systems from other species. However, the dissociation rate of bound insulin cannot be accelerated by the addition of insulin, in contrast with membranes isolated from rat liver. The dissociation rate is strongly dependent on the pH. Although dependent on temperature, the total capacity of binding sites is minimally changed, but the number of high-affinity sites is increased 2-3-fold, by lowering the incubation temperature. These data might be interpreted by assuming a single population of receptors whose distribution between different affinity states depends on temperature. In competition studies, most of the modified insulins examined show a close correlation between binding, determined in plasma membranes from bovine liver, and biological activity, measured in adipocytes. The hypothesis that a positive charge on the A1 residue may be favourable for binding is supported by experiments with an isosteric pair of insulins modified at this residue ([carbamoyl-Gly(A1)]- and [amidino-Gly(A1)]insulin) and with modified insulins carrying one or more positive charges on the A1 residue ([Arg-Gly(A1)]-, [Arg-Arg-Gly(A1)]-, [Arg-Arg-Arg-Gly(A1)]- and [Lys-Arg-Gly(A1)]insulin). The latter insulin derivatives show a higher binding activity for plasma membranes from bovine, porcine and rat liver than expected from their biological activities in adipocytes.

Animals↗
PubMed1980

Transvenous devices for the management of pulmonary embolism.

When anticoagulant treatment of pulmonary embolism is contraindicated or fails, interruption of blood flow through the inferior vena cava offers an alternative method for preventing further embolic episodes. In the past this required abdominal surgery, but currently several clot-capturing devices have been designed for insertion into the human inferior vena cava indirectly via a jugular or femoral venotomy. Another device is being developed for percutaneous delivery through a standard angiographic catheter. In addition to variations in the delivery methods, the form, mechanical effectiveness, and complications of these differ markedly. A suction-cup device is also available for the transvenous removal of pulmonary emboli.

Embolization, Therapeutic↗
PubMed1980

Microleakage of Cavit temporary filling material in endodontic access cavities in monkey teeth.

Sealing properties of Cavit-W temporary filling material were tested in vivo in the control group of a usage experiment in which root canal disinfectants were studied. Histologic examination (Brown and Brenn staining) of the root canals showed a statistical significance in the occurrence of microorganisms with increase in time. Microleakage past the filling material was considered to be responsible.

Animals↗
PubMed1980

Hard-tissue resorption and deposition after endodontic instrumentation.

Hard-tissue resorption and deposition following endodontic instrumentation were studied histologically in forty-one monkey teeth after 2, 7, and 42 days. No medicaments and no root canal filling materials were used. The number and length of lacunae and areas of resorption of the root canal wall, the root surface, and the lamina dura were counted and measured. Resorption, stimulated by instrumentation, was observed after 7 days at all sites. Resorption was slight at the root canal wall and at the root surface and was significantly more severe than normal osteoclastic replacement in the adjacent lamina dura. After 42 days the reaction had subsided at the three sites, but none of the tissue had returned to normal. Inflammatory reaction due to infection of the root canal appeared to enhance resorption after 42 days at the root canal wall and the lamina dura, but this was not observed at the root surface.

Alveolar Process↗
PubMed1980

Analysis of the nucleotide sequence of an invertible controlling element.

The nucleotide sequence of the inversion region responsible for flagellar phase variation in Salmonella was determined. The inversion region is 995 base pairs (bp) in length and is bounded by a 14-bp inverted repeat sequence. A homologous recombination event between the 14-bp inverted repeat sequences would result in the inversion of the DNA segment between them. Sequence homologies with other systems suggest that the 14-bp inverted repeat sequences may have some general significance as sites for specific recombinational events. The gene which specifies H2 flagellin synthesis begins 16 bp outsie the inversion region. Within the inversion region, an open translational frame exists which could encode a low molecualr weight polypeptide (190 amino acids).

Amino Acid Sequence↗
PubMed1980

Critical factors in the chromatographic measurement of glycohemoglobin (HbA1).

Measurement of glycohemoglobin has been proposed as a criterion for the management of diabetes mellitus. We evaluated various conditions critical to the accuracy and precision of the cation-exchange method. Tolerance limits for each variable were defined as follows: phosphate-eluding buffer (0.06 +/- 0.005 mol/L pH 6.70--6.72), column temperature (19--21 degrees C), and resin equilibration (to phosphate buffer, 0.07 mol/l, pH 6.70 +/- 0.01). Hemoglobin absorbance measured in the Sorét region (approximately 416 nm) of the first chromatographic fraction divided by that of the total hemolysate provided the most accurate and precise result. Overall between-run precision expressed as coefficient of variation (CV, in percent) of normal and diabetic pools was 4.8% and 5.1%, respectively. When purified HbA1c was added to hemolysates, recovery was 90--95%. Results were linear to at least 18% glycohemoglobin. Hemoglobin F (HbF) interfered with the method, whereas HbC and HbS did not. Red cells could be stored frozen for at least 6 days, thus easing transport of outpatient samples. A reference range of 6.0--8.8% glycohemoglobin was established from 85 nondiabetic adults (ages 23--65 yr). In a clinical study, only 4 of 13 treated diabetic patients believed to be in good control showed glycohemoglobin results within the normal range. All of the 19 treated diabetics in fair or poor control showed glycohemoglobin results greater than 10% of total Hb, ie., well above the normal range.

Adult↗
PubMed1980

Idiopathic hemochromatosis: a study of biochemical expression in 247 heterozygous members of 63 families: evidence for a single major HLA-linked gene.

The hypothesis has been advanced that the two genes on chromosome 6 determining idiopathic hemochromatosis are not identical alleles and therefore that the disease is not recessively inherited, but rather that two different genes are involved. A study of 63 families points to: (a) the rarity with which a single hemochromatosis gene finds biochemical expression (in only 1 of 5 cases), as revealed through determinations of serum iron, serum ferritin and the desferrioxamine test; (b) no difference in HLA-antigen marking between genes with and those without biochemical expression: (c) no difference other than that produced by chance in the biochemical expression of the two genes in families; and (d) the finding in one highly informative family of identical expression of the two genes. It is concluded that idiopathic hemochromatosis is determined by two homologous alleles in accordance with the classical mode of recessive inheritance.

Adolescent↗