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81.
Summary Kinetic parameters were determined for esterification of dodecanol and decanoic acid in hexane catalysed by lipases from Rhizomucor miehei and Candida rugosa, after pre-equilibration to different values of thermodynamic water activity (aw). Vm increases with increasing aw, but so do the Km values for both substrates. The effect on Km for the alcohol probably represents competition between the first product and the second substrate, as expected for Ping-Pong kinetics. The rise in Km for the acid probably reflects the displacement of water molecules during substrate binding. 相似文献
82.
W. Donald Macrae E. A. Mackinnon H. F. Stich 《In vitro cellular & developmental biology. Plant》1979,15(8):555-564
Summary Sister chromatid exchanges (SCE) and chromosome aberrations were induced in nondividing CHO cells that had been arrested in
their cell cycle by deprivation of the essential amino acid arginine. Cells arrested in arginine-deficient medium (ADM) were
treated with one of the mutagenic agents N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) or mitomycin C (MMC) and refed with complete
medium; the recovering cell population was sampled at various intervals thereafter and mitotic cells analyzed for the presence
of chromosome aberrations and SCE. Both chemicals were observed to cause delays in the cell cycle of recovering cells and
to induce, chromosome aberrations and SCE at low doses. We have described the variation in the incidence of chromosome aberrations
and SCE with respect to sampling time and the number of cell cycles traversed. When ADM-arrested CHO cells were treated with
three mutagens at various intervals either before or after release from ADM, it was observed that: (a) UV light induced the
greatest number of SCE when applied to cells undergoing DNA synthesis, and SCE yeilds induced by this agent could be reduced
by postirradiation incubation in ADM; (b) MNNG induced fewer SCE when applied to cells undergoing DNA synthesis, and SCE yields
induced by this agent could not be reduced by posttreatment incubation in ADM for 24 hr. (c) MMC induced the same level irrespective
of the time of exposure, and SCE yields induced by this agent could not be reduced by posttreatment incubation in ADM for
24 hr.
This work was supported by grants from the British Columbia Foundation for Non-Animal Research (to W. D. M.), and the National
Cancer Institute of Canada and the National Research Council of Canada (to H. F. S.). Professor H. F. Stich is a Research
Associate of the NCI. 相似文献
83.
84.
The diagnostic advantage of fluorescence microscopy (FM) of Papanicolaou-stained cytological specimens obtained by bronchoscopy has been described previously. This study was designed to evaluate the method's diagnostic benefit in cytological preparations of pleural effusions in cases of active pulmonary tuberculosis. In contrast to bronchial material there is no advantage in cytological evaluation of pleural effusions by FM. 相似文献
85.
C A Lessman H R Habibi T H Macrae 《Biology of the cell / under the auspices of the European Cell Biology Organization》1988,64(3):293-299
During the process of progestogen-induced meiotic maturation in the goldfish oocyte, the oocyte nucleus (germinal vesicle, GV) migrates to the sperm entry site or micropyle at the animal pole. Following GV migration (GVM) to the micropyle, the nuclear membrane undergoes dissolution (GVD) and the cell enters metaphase I in preparation to generate the first polar body. Microtubule destabilizing drugs including colcemid, nocodazole and vinblastine were found to elicit GVM, mimicking the process which occurs just prior to the prophase I-metaphase I transition during steroid induced oocyte meiotic maturation. In addition, these drugs enhanced the induction of GVM by 17 alpha, 20 beta dihydroxy-4-pregnen-3-one, a potent, naturally occurring meiotogenic steroid in this species. By contrast, taxol, a microtubule stabilizing drug, was found to inhibit steroid induced GVM. A new assay for centrifugation induced GVM was applied to the goldfish oocyte in order to assess effects of steroids and drugs on GVM, without the complication of GVD or the restrictions imposed by the slow time course of naturally occurring GVM. The effective centrifugal force (ECF) required to elicit GVM in 50% of the oocytes (ECF50) decreased significantly after short incubations (1-5 hr) of oocytes with either 17 alpha,20 beta dihydroxy-4-pregnen-3-one or microtubule disrupting drugs (i.e., colcemid, nocodazole, or vinblastine). A working hypothesis, modeled after the effects of microtubule disrupting agents on intermediate filament arrays in somatic cells, is proposed in which a small number of microtubules or other polymeric tubulin units are responsible for maintaining a cytoskeletal array.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
86.
Katherine Macrae Clare Stretton Christopher Lipina Agnieszka Blachnio-Zabielska Marcin Baranowski Jan Gorski Anna Marley Harinder S. Hundal 《Journal of lipid research》2013,54(9):2366-2378
Chronic exposure of skeletal muscle to saturated fatty acids, such as palmitate (C16:0), enhances proinflammatory IKK-NFκB signaling by a mechanism involving the MAP kinase (Raf-MEK-ERK) pathway. Raf activation can be induced by its dissociation from the Raf-kinase inhibitor protein (RKIP) by diacylglycerol (DAG)-sensitive protein kinase C (PKC). However, whether these molecules mediate the proinflammatory action of palmitate, an important precursor for DAG synthesis, is currently unknown. Here, involvement of DAG-sensitive PKCs, RKIP, and the structurally related monounsaturated fatty acid palmitoleate (C16:1) on proinflammatory signaling are investigated. Palmitate, but not palmitoleate, induced phosphorylation/activation of the MEK-ERK-IKK axis and proinflammatory cytokine (IL-6, CINC-1) expression. Palmitate increased intramyocellular DAG and invoked PKC-dependent RKIPSer153 phosphorylation, resulting in RKIP-Raf1 dissociation and MEK-ERK signaling. These responses were mimicked by PMA, a DAG mimetic and PKC activator. However, while pharmacological inhibition of PKC suppressed PMA-induced activation of MEK-ERK-IKK signaling, activation by palmitate was upheld, suggesting that DAG-sensitive PKC and RKIP were dispensable for palmitate''s proinflammatory action. Strikingly, the proinflammatory effect of palmitate was potently repressed by palmitoleate. This repression was not due to reduced palmitate uptake but linked to increased neutral lipid storage and enhanced cellular oxidative capacity brought about by palmitoleate''s ability to restrain palmitate-induced mitochondrial dysfunction. 相似文献
87.
TM?Matthews RK?Duncan M?Zidanic TH?Michael PA?FuchsEmail author 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2005,191(6):491-503
In the inner ear of birds, as in mammals, reptiles and amphibians, acetylcholine released from efferent neurons inhibits hair cells via activation of an apamin-sensitive, calcium-dependent potassium current. The particular potassium channel involved in avian hair cell inhibition is unknown. In this study, we cloned a small-conductance, calcium-sensitive potassium channel (gSK2) from a chicken cochlear library. Using RT-PCR, we demonstrated the presence of gSK2 mRNA in cochlear hair cells. Electrophysiological studies on transfected HEK293 cells showed that gSK2 channels have a conductance of approximately 16 pS and a half-maximal calcium activation concentration of 0.74±0.17 M. The expressed channels were blocked by apamin (IC50=73.3±5.0 pM) and d-tubocurarine (IC50=7.6±1.0 M), but were insensitive to charybdotoxin. These characteristics are consistent with those reported for acetylcholine-induced potassium currents of isolated chicken hair cells, suggesting that gSK2 is involved in efferent inhibition of chicken inner ear. These findings imply that the molecular mechanisms of inhibition are conserved in hair cells of all vertebrates. 相似文献
88.
Novel bacterial diversity recovered from the rhizosphere of oilseed rape (Brassica napus) determined by the analysis of 16S ribosomal DNA 总被引:3,自引:0,他引:3
Soil was sampled to a distance of 2.5 mm beneath a root mat of oilseed rape (Brassica napus) in a model rhizosphere system. DNA was extracted and the 16S rDNA amplified, cloned and sequenced. Phylogenetic analysis of these sequences with those held on-line, revealed that 37% of the clones fell within the Holophaga / Acidobacterium phylum, 17% were within the proteobacteria, 14% of the clones were close relatives of Bacillus megaterium and 5% were related to Verrucomicrobium spinosum. An additional eleven clones (21%) could not be assigned to any known phylum and may represent novel bacterial lineages. This study highlights the diverse nature of rhizosphere soils and reinforces the role that molecular approaches play in unravelling such diversity. 相似文献
89.
Identification of 40k γ-secalin genes 总被引:1,自引:0,他引:1
90.