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P Chaudhari

Publications and source records attributed to P Chaudhari.

31 records · Page 2Linked to original sources
PubMed1989

Cytochalasin D-mediated hyperinduction of the substrate-associated 52-kilodalton protein p52 in rat kidney fibroblasts.

Regulation of certain differentiated and housekeeping functions in cultured mammalian cells is significantly influenced by cell shape. The shape-modulating agent cytochalasin D (CD) was used, therefore, to elucidate potential cytoarchitectural influences affecting synthesis of a major 52 kDa secreted/substrate-associated protein (p52) of normal rat kidney (NRK) fibroblasts. Biosynthetic labeling experiments indicated that treatment of NRK cells with CD increased, by 10-18-fold, the medium content of an Mr 52,000 protein. Two-dimensional gel electrophoresis and peptide fragment mapping confirmed that the 52 kDa protein produced in abundance as a consequence of CD treatment was identical to p52 constitutively expressed by NRK cells. A lower mw protein (p50; Mr 50,000) was also resolved which, based on pl microheterogeneity, protease fragmentation profile, and sensitivity to tunicamycin, could be identified as a less-glycosylated form of p52. p50 and p52 were both detected in the matrix and medium compartments of NRK and NRK/CD cells. The matrix p52 content of CD-induced and uninduced cells, however, was significantly greater (by 200-500-fold) than the corresponding medium levels. This differential compartmentalization, the time course of p52 accumulation in the matrix of NRK/CD cells compared to its appearance in the medium, and the kinetics of p52 pulse-chase from the matrix collectively indicated that the matrix is the initial site of p52 deposition. Low levels of CD (1 microM) produced extensive disruptions of cellular microfilaments but did not result in an overall cell shape change nor a hyperinduction of p52. Morphologic rounding (seen in 10-100 microM CD) coincided with augmented p52 production. Transition from a flat to a round phenotype in NRK cells, or at least the generation of sufficient microfilament fragmentation to compromise cell-substrate adhesivity, appears to be an essential aspect of CD-mediated p52 hyperinduction.

Animals↗
PubMed1989

Delayed Osmotic Effect on in Vitro Assembly of RuBisCO : Relationship to Large Subunit-Binding Protein Complex Dissociation.

Higher plant ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) cannot reassociate after dissociation, and its subunits do not assemble into active RuBisCO when synthesized in Escherichia coli. Newly synthesized subunits of RuBisCO are associated with a high molecular weight binding protein complex in pea chloroplasts. The immediate donor for large subunits which assemble into RuBisCO is a low molecular weight complex which may be derived from the high molecular weight binding protein complex. When the high molecular weight binding protein complex is diluted, it tends to dissociate, forming low molecular weight complexes. When the large subunit-binding protein complexes were examined after in organello protein synthesis, it was found that the low molecular weight complexes were more abundant when protein synthesis was carried out under hypotonic conditions. This increase in the assembly competent population of low molecular weight large subunit complexes can account for the increased amount of in vitro RuBisCO assembly which occurs under these conditions. The data indicate that the assembly of large subunits into RuBisCO is a function of the aggregation state of the large subunit binding protein complex during protein synthesis. This implies that the binding protein exerts its effects during or shortly after large subunit synthesis.

Journal Article↗
PubMed1988

Incorporation of Large Subunits into Ribulose Bisphosphate Carboxylase in Chloroplast Extracts : Influence of Added Small Subunits and of Conditions during Synthesis.

The incorporation of newly synthesized large subunits into ribulose bisphosphate carboxylase/oxygenase (RuBisCO) in pea chloroplast extracts occurs at the expense of intermediate forms of the large subunit which are complexed with a binding protein. Most subunits of this binding protein are found in dodecameric complexes in chloroplast extracts. Addition of small subunits to these extracts results in approximately 40 to 60% increased incorporation of newly made large subunits into RuBisCO at low or zero concentrations of ATP, but is without significant effect at high concentrations of ATP, a condition in which the dodecameric binding protein complex is dissociated into subunits. Overall, these data support the assumption that the incorporation of large subunits into RuBisCO in chloroplast extracts reflects de novo assembly rather than ;mere' exchange of subunits. The in vitro assembly of large subunits into RuBisCO is a function of the conditions under which the large subunits are synthesized in organello. When the large subunits are made in chloroplasts suspended in 188 millimolar sorbitol, they are approximately 2- to 3-fold better able to assemble into RuBisCO when subsequently incubated in vitro than when they are synthesized in chloroplasts suspended in 375 millimolar sorbitol. This observation indicates that mere synthesis of large subunits is not sufficient to confer maximal assembly competence on large subunits.

Journal Article↗
PubMed1981

Improved detail in biological soft X-ray microscopy: study of blood platelets.

Improved image quality in soft x-ray contact microscopy can be obtained by examining the resist with transmission rather than scanning electron microscopy. Application of the new technique to air-dried preparations of human blood platelets reveals structures not visible in the same cells with transmission electron microscopy or when the resist is examined by scanning electron microscopy. As seen by the new technique, platelet pseudopods contain a central structure connected to a network in the platelet and dense bodies exhibit a lamellar structure.

Blood Platelets↗