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1.
Final steps in the synthesis of platelet activating factor (PAF) occur via two enzymatic reactions: the acetylation of 1-alkyl-2-lyso-sn-glycero-3-phosphocholine by a specific acetyltransferase or the transfer of the phosphocholine base group from CDP-choline to 1-alkyl-2-acetyl-sn-glycerol by a dithiothreitol (DTT)-insensitive cholinephosphotransferase. Our studies demonstrate that rat kidney inner medulla microsomes synthesize PAF primarily via the DTT-insensitive cholinephosphotransferase since the specific activity of this enzyme is greater than 100-fold higher than the acetyltransferase. The two cholinephosphotransferases that catalyze the biosynthesis of phosphatidylcholine and PAF have similar Mg2+ or Mn2+ requirements and are inhibited by Ca2+. Also topographic experiments indicated that both activities are located on the cytoplasmic face of microsomal vesicles. PAF synthesis was slightly stimulated by 10 mM DTT, whereas the enzymatic synthesis of phosphatidylcholine was inhibited greater than 95% under the same conditions. The concept of two separate enzymes for PAF and phosphatidylcholine synthesis is further substantiated by the differences in the two microsomal cholinephosphotransferase activities with respect to pH optima, substrate specificities, and their sensitivities to temperature, deoxycholate, or ethanol. Study of the substrate specificities of the DTT-insensitive cholinephosphotransferase showed that the enzyme prefers a lipid substrate with 16:0 or 18:1 sn-1-alkyl chains. Short chain esters at the sn-2 position (acetate or propionate) are utilized by the DTT-insensitive cholinephosphotransferase, but analogs with acetamide or methoxy substituents at the sn-2 position are not substrates. Also, CDP-choline is the preferred water-soluble substrate when compared to CDP-ethanolamine. Utilization of endogenous neutral lipids as a substrate by the DTT-insensitive cholinephosphotransferase demonstrated that sufficient levels of alkylacetylglycerols are normally present in rat kidney microsomes to permit the synthesis of physiological quantities of PAF. These data suggest the renal DTT-insensitive cholinephosphotransferase could be a potentially important enzyme in the regulation of systemic blood pressure. 相似文献
2.
Decrease in ovarian platelet-activating factor during ovulation in the gonadotropin-primed immature rat 总被引:1,自引:0,他引:1
Platelet-activating factor (PAF) is a biologically active phospholipid that is released locally during acute inflammatory reactions and tissue injury. Since there is evidence that the biochemical events of mammalian ovulation resemble an inflammatory reaction, the objective of this study was to determine whether ovarian levels of PAF change during ovulation. At 2-h intervals during the ovulatory process in gonadotropin-primed 25-day-old Wistar rats, the ovaries were extirpated, homogenized, and extracted for lipids. The extracts were subjected to thin-layer chromatography (TLC), and the portion of the silica gel that comigrated with PAF was re-extracted and assayed for PAF activity. The PAF was measured (in fmole equivalents of synthetic PAF) by a bioassay based on the capacity of aliquots of the extracts to release [3H]-serotonin from platelets isolated from whole blood of rabbits and prelabeled with [3H]-serotonin. The ovarian level of PAF decreased (p less than 0.01) by 36% from 6.67 +/- 0.77 to 4.27 +/- 0.45 fmoles/mg ovary by 2 h after treatment with human chorionic gonadotropin (hCG), and it declined another 14% by 4 h after hCG. The ovarian PAF remained at this reduced level for up to 24 h after hCG. The administration of indomethacin (5 mg/rat, s.c.) or epostane (5 mg/rat, s.c.) at 1 h after hCG prevented ovulation, but neither drug affected the decline in ovarian PAF. Preliminary tests showed that the lipid extracts from the ovaries also contained PAF inhibitor(s) that comigrated with PAF on the TLC plates. Similar to PAF, the lipid-soluble inhibitor(s) decreased (p less than 0.05) in the ovaries within 4 h after hCG treatment.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
3.
Genetic Analysis of Olfactory Behavior in Drosophila: A New Screen Yields the Ota Mutants 总被引:5,自引:3,他引:2 下载免费PDF全文
A simple means of measuring Drosophila olfactory response is described, and the behavior which it measures is characterized. The assay was used to screen for X-linked mutants defective in olfactory function. Six ota mutants were isolated and characterized (ota = olfactory trap abnormal). Four of the mutants were found to be abnormal in another chemosensory behavior as well. Two of the mutant phenotypes extend to include another sensory system: they are defective in visual system physiology. All were normal, however, in a test of giant fiber system physiology. Two of the mutations are dominant, and the recessive mutations define two complementation groups. Mutations representing each complementation group, as well as one of the dominant mutations, were mapped. For the mutants with defective visual system physiology, the visual defects were shown to cosegregate with olfactory phenotypes. 相似文献
4.
4′,5′-Unsaturated nucleosides are obtained by the action of 1,5-diazabicyclo-[5.4.0]undec-5-ene on N1- and N3-(methyl 2,3,4-tri-O-acetyl-β-d-glucopyranosyluronate)-5-fluorouracil. The 2H1 conformation of N1- and N3-(methyl 4-deoxy-α-l-threo-hex-4-enopyranosyluronate)-5-fluorouracil has been established by 1H-n.m.r. and c.d. methods. Interaction of the heterocyclic base and the double bond of the sugar moiety is demonstrated. 相似文献
5.
Isolation and characterization of a large,neurite-associated glycoconjugate from neuroblastoma cells 下载免费PDF全文
A high molecular weight glycoconjugate has been isolated from neurite-producing neuronal tumor cells in culture and has been designated as I(0) based on its elution characteristics in gel filtration chromatography. This molecule cannot be found in a variety of nonneuronal cells. I(0) is found in the substratum-attached material or cell fraction of neurite-producing neuroblastoma cells, depending upon culture conditions. It is found in the substratum-bound fraction of B104 rat neuroblastoma cells during serum starvation and in the EGTA-detached cell fraction of B104 cells grown in chemically defined N2 medium. It occurs only in the cell fraction of the human neuroblastoma line Platt. Examination of behavioral variants of the B104 rat line further strengthens the association of I(0) with neurite production; the constitutive neurite-producing E(R)B9 variant contains I(0) while the non-neurite-producing E(R)A11 variant does not. I(0) is large, eluting in the void volume of sepharose-CL2B columns. Radioiodination of intact cells with lactoperoxidase shows I(0) to be a cell surface component. Metabolic radiolabeling studies show that it contains a high proportion of polysaccharide to protein, does not contain mannose, and is unsulfated. Alkaline borohydride reduction release two size classes of large polysaccharide chain. The alkaline reduction results, along with the mannose incorporation studies, show the presence of O-glycosidic linkages and few, if any, N-linkages. Resistance to nitrous acid deamination, insensitivity to glycosaminoglycan lyases, and the absence of sulfation, indicate that I(0) does not contain the glycosaminoglycans hyaluronic acid, chondroitin-, dermatan-, or heparin- sulfates. Affinity column chromatography reveals high binding affinity of I(0) to polyornithine and no binding to gelatin (collagen) or the glycosaminoglycans hyaluronate and heparin. These studies describe a unique high molecular weight glycoconjugate on the surface of neurite-producing neuroblastoma cell lines from two species. 相似文献
6.
7.
Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal 总被引:10,自引:9,他引:1
We have developed a new approach to the measurement of phylogenetic signal
in character state matrices called relative apparent synapomorphy analysis
(RASA). RASA provides a deterministic, statistical measure of natural
cladistic hierarchy (phylogenetic signal) in character state matrices. The
method works by determining whether a measure of the rate of increase of
cladistic similarity among pairs of taxa as a function of phenetic
similarity is greater than a null equiprobable rate of increase. Our
investigation of the utility and limitations of RASA using simulated and
bacteriophage T7 data sets indicates that the method has numerous
advantages over existing measures of signal. A first advantage is
computational efficiency. A second advantage is that RASA employs known
methods of statistical inference, providing measurable sensitivity and
power. The performance of RASA is examined under various conditions of
branching evolution as the number of characters, character states per
character, and mutations per branch length are varied. RASA appears to
provide an unbiased and reliable measure of phylogenetic signal, and the
general approach promises to be useful in the development of new techniques
that should increase the rigor and reliability of phylogenetic estimates.
相似文献
8.
J. R. Riesgo-Escovar C. Woodard J. R. Carlson 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1994,175(6):687-693
We describe the kinetics of odorant response in the maxillary palp of Drosophila, and show that the rate of recovery from odorant stimulation is affected by mutation of the rdgB (retinal degeneration B) gene. We use immunocytochemistry to confirm that the rdgB gene product is expressed in the maxillary palp. rdgB has recently been shown to encode a protein with Ca2+-binding sites and sequence similarity to rat brain phosphatidylinositol transfer protein; it is located near the rhabdomeric membranes in photoreceptor cells, where it has been suggested to play a role in membrane transport. The delay in recovery kinetics that we observe in olfactory tissue may reflect a defect in membrane restoration at the conclusion of the olfactory transduction cascade. The use of common molecules in the physiology of two olfactory organs, and in both visual and olfactory physiology, is discussed.Abbreviations
EAG
electroantennogram
-
EPG
electropalpogram
-
ERG
electroretinogram
-
norpA
no receptor potential A
-
PBS
phosphate buffered saline
-
rdgB
retinal degeneration B
-
PI
phosphatidylinositol 相似文献
9.
Molecular evolution of voltage-sensitive ion channel genes: on the origins of electrical excitability 总被引:14,自引:0,他引:14
We have analyzed nucleic acid and amino acid sequence alignments of a
variety of voltage-sensitive ion channels, using several methods for
phylogenetic tree reconstruction. Ancient duplications within this family
gave rise to three distantly related groups, one consisting of the Na+ and
Ca++ channels, another the K+ channels, and a third including the cyclic
nucleotide-binding channels. A series of gene duplications produced at
least seven mammalian homologues of the Drosophila Shaker K+ channel;
clones of only three of these genes are available from all three mammalian
species examined (mouse, rat, and human), pointing to specific genes that
have yet to be recovered in one or another of these species. The
Shaw-related K+ channels and the Na+ channel family have also undergone
considerable expansion in mammals, relative to flies. These expansions
presumably reflect the needs of the high degree of physiological and
neuronal complexity of mammals. Analysis of the separate domains of the
four-domain channels (Ca++ and Na+) supports their having evolved by two
sequential gene duplications and implies the historical existence of a
functional two-domain channel.
相似文献
10.
mtDNA diversity in rhesus monkeys reveals overestimates of divergence time and paraphyly with neighboring species 总被引:4,自引:0,他引:4
Reconstructions of the human-African great ape phylogeny by using
mitochondrial DNA (mtDNA) have been subject to considerable debate. One
confounding factor may be the lack of data on intraspecific variation. To
test this hypothesis, we examined the effect of intraspecific mtDNA
diversity on the phylogenetic reconstruction of another Plio- Pleistocene
radiation of higher primates, the fascicularis group of macaque (Macaca)
monkey species. Fifteen endonucleases were used to identify 10 haplotypes
of 40-47 restriction sites in M. mulatta, which were compared with similar
data for the other members of this species group. Interpopulational,
intraspecific mtDNA diversity was large (0.5%- 4.5%), and estimates of
divergence time and branching order incorporating this variation were
substantially different from those based on single representatives of each
species. We conclude that intraspecific mtDNA diversity is substantial in
at least some primate species. Consequently, without prior information on
the extent of genetic diversity within a particular species, intraspecific
variation must be assessed and accounted for when reconstructing primate
phylogenies. Further, we question the reliability of hominoid mtDNA
phylogenies, based as they are on one or a few representatives of each
species, in an already depauperate superfamily of primates.
相似文献