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51.
Tricarboxylic Acid Cycle Enzymes and Morphogenesis in Blastocladiella emersonii 总被引:2,自引:6,他引:2 下载免费PDF全文
During exponential growth, ordinary colorless (OC) plants of Blastocladiella emersonii consumed little glucose and produced no lactic acid. Similarly, resistant sporangial (RS) plants did not utilize glucose or produce lactic acid during the first 24 hr of exponential growth. During the next 24 hr of RS development, glucose was consumed with the concomitant production of lactic acid which was then reutilized. Lactic acid gradually accumulated again at maturity. Enzyme studies on cell-free extracts indicated the presence of all tricarboxylic cycle enzymes except α-ketoglutarate dehydrogenase at all stages of development of both RS and OC plants. Included among the enzymes detected were an adenosine monophosphate-stimulated, nicotinamide adenine dinucleotide-isocitric dehydrogenase, and citrate-condensing enzyme. When measured on a per plant basis, tricarboxylic cycle enzyme levels increased during the exponential growth of both kinds of plants. Only after the bicarbonate ceased to have effect on RS plant morphogenesis was there a decrease in the levels of the tricarboxylic cycle enzymes when measured on a per plant basis. Specific activity measurements indicated some differences in the differential rates of synthesis among the enzymes studied previous to 36 hr. Preliminary studies utilizing short periods of 14C-bicarbonate fixation in young RS plants indicated that during the first 4 min most of the label was located in aspartic acid. These results are discussed in terms of previous results and particularly Cantino's hypothesis concerning the relationship between bicarbonate induction and tricarboxylic-cycle enzymes in the morphogenesis of B. emersonii. 相似文献
52.
McCurdy DW 《Protoplasma》1999,209(1-2):120-125
The effectiveness of 2,3-butanedione monoxime (BDM) as an inhibitor of plant myosins has been investigated. Three myosin-dependent motility phenomena in plants, namely cytoplasmic streaming in Chara corallina, light-dependent chloroplast repositioning in Elodea sp., and brefeldin A(BFA)-induced Golgi membrane dynamics in wheat (Triticum aestivum L. cv. Kite) root-tip cells were investigated. All three processes were inhibited by the sulfhydryl-modifying agent N-ethylmalemide (NEM), indicating the probable involvement of myosin as the motor protein in each case. However, none of these myosin-dependent processes were inhibited by BDM at concentrations as high as 20 mM in some instances. These results therefore question the general usefulness of BDM as an inhibitor of myosin-based activities in plant cells. 相似文献
53.
The catalytic domains of murine Golgi alpha1,2-mannosidases IA and IB that
are involved in N-glycan processing were expressed as secreted proteins in
P.pastoris . Recombinant mannosidases IA and IB both required divalent
cations for activity, were inhibited by deoxymannojirimycin and
kifunensine, and exhibited similar catalytic constants using
Manalpha1,2Manalpha-O-CH3as substrate. Mannosidase IA was purified as a 50
kDa catalytically active soluble fragment and shown to be an inverting
glycosidase. Recombinant mannosidases IA and IB were used to cleave
Man9GlcNAc and the isomers produced were identified by high performance
liquid chromatography and proton-nuclear magnetic resonance spectroscopy.
Man9GlcNAc was rapidly cleaved by both enzymes to Man6GlcNAc, followed by a
much slower conversion to Man5GlcNAc. The same isomers of Man7GlcNAc and
Man6GlcNAc were produced by both enzymes but different isomers of
Man8GlcNAc were formed. When Man8GlcNAc (Man8B isomer) was used as
substrate, rapid conversion to Man5GlcNAc was observed, and the same
oligosaccharide isomer intermediates were formed by both enzymes. These
results combined with proton-nuclear magnetic resonance spectroscopy data
demonstrate that it is the terminal alpha1, 2-mannose residue missing in
the Man8B isomer that is cleaved from Man9GlcNAc at a much slower rate.
When rat liver endoplasmic reticulum membrane extracts were incubated with
Man9GlcNAc2, Man8GlcNAc2was the major product and Man8B was the major
isomer. In contrast, rat liver Golgi membranes rapidly cleaved
Man9GlcNAc2to Man6GlcNAc2and more slowly to Man5GlcNAc2. In this case all
three isomers of Man8GlcNAc2were formed as intermediates, but a distinctive
isomer, Man8A, was predominant. Antiserum to recombinant mannosidase IA
immunoprecipitated an enzyme from Golgi extracts with the same specificity
as recombinant mannosidase IA. These immunodepleted membranes were enriched
in a Man9GlcNAc2to Man8GlcNAc2- cleaving activity forming predominantly the
Man8B isomer. These results suggest that mannosidases IA and IB in Golgi
membranes prefer the Man8B isomer generated by a complementary mannosidase
that removes a single mannose from Man9GlcNAc2.
相似文献
54.
Pascal J. Delaquis Douglas E. Caldwell John R. Lawrence Alan R. McCurdy 《Microbial ecology》1989,18(3):199-210
The effects of glucose and nitrogen depletion on the colonization of glass Petri plates byPseudomonas fluorescens were studied in batch culture. Colonization of the surfaces was initiated before colonization of the bulk phase, and biofilm formation was observed. This resulted in an apparent lag in the batch growth curve for the cell suspension. The lag phase was an artifact caused by the partitioning of cells between the bulk and solid phase of the culture and was not due to a reduction in the growth rate of unattached cells. The specific growth rate of the unattached cells (0.331 hour–1) was almost twice that determined for the total population (0.171 hour–1). Consequently the growth rate of biofilm-forming bacteria cannot be determined in batch culture unless the growth of both attached and unattached cells is monitored, and batch growth curves may contain artifacts due to the formation and dispersion of biofilms. The depletion of either glucose or nitrogen led to the active detachment of cells from the biofilm. An increase in the hydrophobicity of unattached cells was noted on depletion of carbon. This increase was the result of emigration of cells from the surface into the bulk phase.Paper contribution number 128, Centre de Rechcrches Alimentaires de St Hyacinthe. 相似文献
55.
Summary Ca2+-dependent protein kinase (CDPK) has been proposed to mediate inhibition by Ca2+ of cytoplasmic streaming in the green algaChara. We have identified the in vivo substrate(s) of CDPK inChara by using vacuolar perfusion of individual internodal cells with [-32P]ATP. Phosphorylation of several polypeptides is enhanced when perfusions are performed at 10–4M free Ca2+ compared to <10–9M free Ca2+. The Ca2+-stimulated phosphorylation of these proteins is inhibited by the presence of a monoclonal antibody to soybean CDPK. One of these proteins is 16 to 18kDa and is recognized by an antibody against gizzard myosin light chains. These results demonstrate that inChara, several polypeptides are phophorylated by CDPK and one of these proteins has been tentatively identified as a myosin light chain. These observations support the hypothesis that Ca2+-regulated phosphorylation of myosin is involved in the regulation of cytoplasmic streaming.Abbreviations CDPK
calcium-dependent protein kinase
- mAb
monoclonal antibody 相似文献
56.
The actin cytoskeleton coordinates numerous cellular processes required for plant development. The functions of this network are intricately linked to its dynamic arrangement, and thus progress in understanding how actin orchestrates cellular processes relies on critical evaluation of actin organization and turnover. To investigate the dynamic nature of the actin cytoskeleton, we used a fusion protein between green fluorescent protein (GFP) and the second actin-binding domain (fABD2) of Arabidopsis (Arabidopsis thaliana) fimbrin, AtFIM1. The GFP-fABD2 fusion protein labeled highly dynamic and dense actin networks in diverse species and cell types, revealing structural detail not seen with alternative labeling methods, such as the commonly used mouse talin GFP fusion (GFP-mTalin). Further, we show that expression of the GFP-fABD2 fusion protein in Arabidopsis, unlike GFP-mTalin, has no detectable adverse effects on plant morphology or development. Time-lapse confocal microscopy and fluorescence recovery after photobleaching analyses of the actin cytoskeleton labeled with GFP-fABD2 revealed that lateral-filament migration and sliding of individual actin filaments or bundles are processes that contribute to the dynamic and continually reorganizing nature of the actin scaffold. These new observations of the dynamic actin cytoskeleton in plant cells using GFP-fABD2 reveal the value of this probe for future investigations of how actin filaments coordinate cellular processes required for plant development. 相似文献
57.
Summary Actin microfilaments in isolated root-tip cells from wheat (Triticum aestivum L. cv. Kite) were visualized by immunofluorescence microscopy using two different antiactin monoclonal antibodies. Cells in interphase contain predominantly subcortical bundles of microfilaments, as described in many cell types, but in preprophase and prophase cells, immunodetectable actin is organized solely in ordered arrays of cortical microfilaments that cover the entire surface of the cell, transverse on lateral faces, random on end walls. Intermediate stages with random and transverse microfilaments are also seen on lateral faces. The cell cycle stage-dependent transverse cortical microfilaments described here are previously unreported in higher plant cells.Abbreviations Ig
immunoglobulin
- MF
microfilament 相似文献
58.
Actin and actin-binding proteins in higher plants 总被引:18,自引:0,他引:18
Summary The actin cytoskeleton is a complex and dynamic structure that participates in diverse cellular events which contribute to plant morphogenesis and development. Plant actins and associated actin-binding proteins are encoded by large, differentially expressed gene families. The complexity of these gene families is thought to have been conserved to maintain a pool of protein isovariants with unique properties, thus providing a mechanistic basis for the observed diversity of plant actin functions. Plants contain actin-binding proteins which regulate the supramolecular organization and function of the actin cytoskeleton, including monomer-binding proteins (profilin), severing and dynamizing proteins (ADF/cofilin), and side-binding proteins (fimbrin, 135-ABP/villin, 115-ABP). Although significant progress in documenting the biochemical activities of many of these classes of proteins has been made, the precise roles of actin-binding proteins in vivo awaits clarification by detailed mutational analyses.Dedicated to Professor Brian E. S. Gunning on the occasion of his 65th birthday 相似文献
59.
60.