RESUMO
Crude brain homogenates of terminally diseased hamsters infected with the 263 K strain of scrapie (PrP Sc) were heated and/or pressurized at 800 MPa at 60 degrees C for different times (a few seconds or 5, 30, 120 min) in phosphate-buffered saline (PBS) of different pH and concentration. Prion proteins were analyzed on immunoblots for their proteinase K (PK) resistance, and in hamster bioassays for their infectivity. Samples pressurized under initially neutral conditions and containing native PrP Sc were negative on immunoblots after PK treatment, and a 6-7 log reduction of infectious units per gram was found when the samples were pressurized in PBS of pH 7.4 for 2 h. A pressure-induced change in the protein conformation of native PrP Sc may lead to less PK resistant and less infectious prions. However, opposite results were obtained after pressurizing native infectious prions at slightly acidic pH and in PBS of higher concentration. In this case an extensive fraction of native PrP Sc remained PK resistant after pressure treatment, indicating a protective effect possibly due to induced aggregation of prion proteins in such buffers.
Assuntos
Endopeptidase K/química , Pressão Hidrostática , Proteínas PrPSc/química , Animais , Encéfalo/metabolismo , Soluções Tampão , Fenômenos Químicos , Físico-Química , Cricetinae , Endopeptidase K/metabolismo , Concentração de Íons de Hidrogênio , Proteínas PrPSc/metabolismo , Proteínas PrPSc/patogenicidade , Fatores de TempoRESUMO
Crude brain homogenates of terminally diseased hamsters infected with the 263 K strain of scrapie (PrP Sc) were heated and/or pressurized at 800 MPa at 60°C for different times (a few seconds or 5, 30, 120 min) in phosphate-buffered saline (PBS) of different pH and concentration. Prion proteins were analyzed on immunoblots for their proteinase K (PK) resistance, and in hamster bioassays for their infectivity. Samples pressurized under initially neutral conditions and containing native PrP Sc were negative on immunoblots after PK treatment, and a 6-7 log reduction of infectious units per gram was found when the samples were pressurized in PBS of pH 7.4 for 2 h. A pressure-induced change in the protein conformation of native PrP Sc may lead to less PK resistant and less infectious prions. However, opposite results were obtained after pressurizing native infectious prions at slightly acidic pH and in PBS of higher concentration. In this case an extensive fraction of native PrP Sc remained PK resistant after pressure treatment, indicating a protective effect possibly due to induced aggregation of prion proteins in such buffers.
Assuntos
Animais , Cricetinae , Endopeptidase K/química , Pressão Hidrostática , Proteínas PrPSc/química , Soluções Tampão , Encéfalo/metabolismo , Físico-Química , Endopeptidase K/metabolismo , Concentração de Íons de Hidrogênio , Proteínas PrPSc/metabolismo , Proteínas PrPSc/patogenicidade , Fatores de TempoRESUMO
The purpose of this study is to examine the mesiodistal and buccolingual crown dimensions in three populations--57 subjects (35 boys and 22 girls) from Iowa City, Iowa; 54 subjects (30 boys and 24 girls) from Alexandria, Egypt; and 60 subjects (26 boys and 34 girls) from Chihuahua, Mexico. All subjects had normal Class I occlusion, with no history of orthodontic treatment. Comparisons of single teeth as well as sums of groups of teeth were performed between boys and girls within and between the two populations. The analysis of variance general linear models procedure was used for statistical comparisons. The findings from this investigation indicated that (1) differences between antimeres are of small magnitude and of no statistical significance; (2) all populations have significant differences in tooth dimensions between the sexes with boys having larger canines and first molars; (3) there is greater variation in the buccolingual than in the mesiodistal dimensions among the three populations; (4) there is a greater similarity in tooth dimensions among the boys from the three populations than among the girls, but the magnitude of these differences is considered to be of little clinical significance; and (5) standards for the buccolingual diameters were developed for the three populations. As a result, it was concluded that prediction equations used for space analysis in the mixed dentition to determine tooth size-arch length discrepancies in the Iowa population can also be used for persons from Egypt and from the northern part of the Mexican Republic, with some suggested modifications.
Assuntos
Dente/anatomia & histologia , Adolescente , Dente Pré-Molar/anatomia & histologia , Criança , Dente Canino/anatomia & histologia , Egito , Feminino , Humanos , Iowa , Masculino , México , Variações Dependentes do Observador , Odontometria , Fatores SexuaisRESUMO
Measurement of crown width of the teeth from first molar to first molar in population samples from Northern Mexico and North Central United States finds only small differences that would be of little importance in orthodontic diagnosis.