Biomedical subjects
Publications and source records attributed to R Vallee.
Dynein is a large enzyme complex that has been found in recent years to be responsible for a variety of forms of intracellular movement associated with microtubules. Molecular analysis of several of the polypeptide components of dynein and a related complex has provided important new insight into their structural organization and mechanism of action in the cell.
The effects of chewing efficiency on nutrient intake and the prevalence of gastrointestinal disorders were determined in edentulous elderly subjects. Three hundred sixty-seven noninstitutionalized individuals aged 60 years and over were interviewed. Denture masticatory performance and the collection of dietary information were assessed with the "Swallowing Threshold Test Index" and a food-frequency questionnaire. Approximately half (47%) of the participants exhibited a low masticatory performance classification. Thirty-nine percent used the same prosthesis for more than 10 years and 28% were taking some medication for gastrointestinal disorders. Lower intakes of fruits and vegetables for both sexes and of vitamin A by women were observed in subjects with poor masticatory performance. Furthermore, subjects with poor masticatory performance took significantly more drugs (37%) than those with superior performance (20%). A reduced consumption of high-fiber foods could therefore induce the development of gastrointestinal disorders in edentulous elderly subjects with a deficient masticatory performance.
Phosphorylation by protein kinases has been established as a key factor in the regulation of cytoskeletal structure. However, little is known about the role of protein phosphatases in cytoskeletal regulation. To assess the possible functions of protein phosphatases in this respect, we studied the effects of the phosphatase inhibitors calyculin A, okadaic acid, and dinophysistoxin 1 (35-methylokadaic acid) on BHK-21 fibroblasts. Within minutes of incubation with these inhibitors, changes are seen in the structural organization of intermediate filaments, followed by a loss of microtubules, as assayed by immunofluorescence. These changes in cytoskeletal structure are accompanied by a rapid and selective increase in vimentin phosphorylation on interphase-specific sites, and they are fully reversible after removal of calyculin A. The results indicate that there is a rapid phosphate turnover on cytoskeletal intermediate filaments and further suggest that protein phosphatases are essential for the maintenance and structural integrity of two major cytoskeletal components.
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Hirano bodies are filamentous, paracrystalline inclusions that are found in dendrites and cell bodies of neurons in Alzheimer's and other neurodegenerative diseases. Actin appears to be a major component of these structures. We present evidence that tropomyosin and high molecular weight microtubule-associated proteins (MAPs) are also components of Hirano bodies. Although an association between actin and MAPs has been noted in vitro, interactions in vivo have not heretofore been demonstrated. Since microtubules are not present in Hirano bodies, and anti-tubulin and anti-neurofilament antibodies do not bind to Hirano bodies, the association between MAPs and these inclusions is likely a result of interactions between MAPs and actin, and not MAPs and microtubules or neurofilaments.
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Chymotryptic fragments of microtubule-associated protein 2 (MAP 2) containing the portion of the molecule responsible for promoting microtubule assembly were identified. These assembly-promoting fragments displaced intact MAP 2, but not MAP 1, from assembled microtubules. This indicates that the association of MAP 2 with the microtubule surface is reversible. Both the assembly-promoting fragments and fragments representing the portion of the MAP 2 molecule observed as a projection on the microtubule surface were found to contain sites for endogenous cyclic AMP-dependent phosphorylation. The projection fragments were capable of endogenous phosphorylation even after their physical separation from microtubules. This suggests an intimate association of a kinase activity with the projections. Detailed analysis of the properties of the chymotryptic fragments of MAP 2 has led to a map of the molecule showing the major sites of proteolytic attack and the sites of phosphorylation.
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