Paradoxical activation of c-Src as a drug-resistant mechanism

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Polypeptide Composition of Envelopes of Spinach Chloroplasts: Two Major Proteins Occupy 90% of Outer Envelope Membranes

Outer and inner envelope membranes of spinach chloroplasts wereisolated using floatation centrifugation followed by sedimentationsucrose density gradient centrifugation after disruption ofintact chloroplasts by freezing and thawing. Two major fractionswith buoyant densities of 1.11 and 1.08 g cm^–3 and a minorfraction with a density of 1.15 g cm^–3 were obtained.They were identified as innei and outer envelope and thylakoidfractions, respectively, by analyzing their polypeptide compositionby high-resolution SDS-PAGE and the N-terminal sequences oftheir protein components. Due to the refinement of the isolation procedure, most of theribulose-l,5-bisphosphate carboxylase/oxygenasc (RuBisCO), whichhad always been observed as a contaminant, was eliminated fromthe outer envelope fraction. Application of high-resolutionSDS-PAGE revealed that this fraction was rich in the low-molecular-massouter envelope protein, E6.7 [Salomon et at. (1990) Proc. Natl.Acad. Sci. USA 87: 5778] and a protein with a molecular massof 15 kDa which is homologous to the 16 kDa outer envelope proteinof pea [Pohlmeyer et al. (1997) Proc. Natl. Acad. Sci. USA 94:9504]. The two proteins account for 90% of the total proteinspresent in outer envelope membranes. Proteins which are suggestedto function in translocation of nuclear-encoded polypeptideswere not identified in the envelopes from spinach in the presentstudy. Differences in the protein composition of outer envelopemembranes arc discussed based on the developemental stages ofchloroplasts. ¹Present address: Biological Function Section, Kansai AdvancedResearch Center, Communications Research Laboratory, Ministryof Posts and Telecommunications, Kobe, Hyogo, 651-24 Japan.     

Increases in the fluorescence Fo level and reversible inhibition of Photosystem II reaction center by high-temperature treatments in higher plants

Effects of high temperatures on the fluorescence F_m (maximum fluorescence) and F_o (dark level fluorescence) levels were studied and compared with those of the photochemical reactions of PS II. These comparisons were performed during and after the high temperature treatments. The following results were obtained; (1) increases in the F_o level at high temperatures were partly reversible, (2) the F_m level in the presence of dithionite in spinach chloroplasts decreased at high temperatures and also showed a partial reversibility, (3) photoreductions of pheophytin a and Q_a were reversibly inhibited at high temperatures parallel to the decrease in the difference between the F_m and F_o levels, and (4) the decrease in the fluorescence F_m level seemed to be related to denaturation of chlorophyll-proteins. All the data suggested that, as well as the separation of light-harvesting chlorophyll a/t b protein complexes of PS II from the PS II core complexes, partly reversible inactivation of the PS II reaction center at high temperatures is the cause of the increase in the F_o level.     

Putative regulatory mechanism of prothoracicotropic hormone (PTTH) secretion in the American cockroach, <Emphasis Type="Italic">Periplaneta americana</Emphasis> as inferred from co-localization of Rab8, PTTH,and protein kinase C in neurosecretory cells

Small GTPases of the Rab family act as essential regulators of vesicle transport pathways, including the exocytosis of neurohormones. These processes are not well-understood in insects. To address the physiological function of Rab proteins and their phosphorylation in insect neurosecretion, Rab8-like, prothoracicotropic hormone (PTTH)-like, and protein kinase C (PKC)-like immunohistochemical reactivities (-ir) were investigated in the brain of the American cockroach, Periplaneta americana. All the antibodies tested reacted with neurons in the pars intercerebralis, corpora cardiaca, and nervi corporis allati I. Double-labeling experiments demonstrated that all PTTH-ir were colocalized with Rab8-ir and PKC-ir in the pars intercerebralis, although exclusive reactivity was present to antisera against Rab8 or PKC. These findings support the notion that Rab8-like antigen is phosphorylated by PKC, and that this phosphorylation is involved in the axonal transport and secretion of PTTH in this species. This work was supported by a Grant-in-Aid for Scientific Research (B) 1838043, (C) 20580053, and Global Center of Education and Research Program (19GCOE01) from the Japan Society for the Promotion of Science.