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81.
Jonathan A. Lindquist Elisabeth Barofsky Philip N. McFadden 《Journal of Protein Chemistry》1996,15(1):115-122
Protein (d-aspartyl/l-isoaspartyl) carboxyl methyltransferase (PCM, E.C. 2.1.1.77) was previously shown to be enzymatically methyl esterified in an autocatalytic manner at altered aspartyl residues; methyl esters are observed in a subpopulation of the enzyme termed thePCM fraction [Lindquist and McFadden (1994),J. Protein Chem.
13, 23–30]. The altered aspartyl sites serving as methyl acceptors inPCM have now been localized by using proteolytic enzymes and chemical cleavage techniques in combination with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to identify fragments of the [3H]automethylated enzyme that contain a [3H]methyl ester. Methylation was positively identified at positions Asn188 and Asp217 in the enzyme sequence, a consequence of the spontaneous alteration of these sites tol-isoaspartyl ord-aspartyl sites and their methylation by active PCM molecules. The identification of more than one site of automethylation shows thatPCM is not a homogeneous population of damaged PCM molecules, but rather a complex population of molecules with a variety of age-altered damage sites.Abbreviations PCM
protein (d-aspartyl/l-isoaspartyl) carboxyl methyltransferase
- EDTA
disodium ethylenediaminetetraacetate
- PMSF
phenylmethylsulfonyl fluoride
- TEA
trifluoroacetic acid
- HPLC
high-pressure liquid chromatography 相似文献
82.
Luke Olsen Jonathan A. Sherratt Philip K. Maini 《Bulletin of mathematical biology》1996,58(4):787-808
The normal process of dermal wound healing fails in some cases, due to fibro-proliferative disorders such as keloid and hypertrophic
scars. These types of abnormal healing may be regarded as pathologically excessive responses to wounding in terms of fibroblastic
cell profiles and their inflammatory growth-factor mediators. Biologically, these conditions are poorly understood and current
medical treatments are thus unreliable.
In this paper, the authors apply an existing deterministic mathematical model for fibroplasia and wound contraction in adult
mammalian dermis (Olsenet al., J. theor. Biol.
177, 113–128, 1995) to investigate key clinical problems concerning these healing disorders. A caricature model is proposed which
retains the fundamental cellular and chemical components of the full model, in order to analyse the spatiotemporal dynamics
of the initiation, progression, cessation and regression of fibro-contractive diseases in relation to normal healing. This
model accounts for fibroblastic cell migration, proliferation and death and growth-factor diffusion, production by cells and
tissue removal/decay.
Explicit results are obtained in terms of the model processes and parameters. The rate of cellular production of the chemical
is shown to be critical to the development of a stable pathological state. Further, cessation and/or regression of the disease
depend on appropriate spatiotemporally varying forms for this production rate, which can be understood in terms of the bistability
of the normal dermal and pathological steady states—a central property of the model, which is evident from stability and bifurcation
analyses.
The work predicts novel, biologically realistic and testable pathogenic and control mechanisms, the understanding of which
will lead toward more effective strategies for clinical therapy of fibro-proliferative disorders. 相似文献
83.
Sojourners: The Return of German Jews and the Question of Identity. John Borneman and Jeffrey M. Peck. Lincoln
Recovered Roots: Collective Memory and the Making of Israeli National Tradition. Yael Zerubavel. Chicago
The Masada Myth: Collective Memory and Mythmaking in Israel. Nachman Ben-Yehuda. Madison 相似文献
Recovered Roots: Collective Memory and the Making of Israeli National Tradition. Yael Zerubavel. Chicago
The Masada Myth: Collective Memory and Mythmaking in Israel. Nachman Ben-Yehuda. Madison 相似文献
84.
Identification of molecular markers in soybean comparing RFLP,RAPD and AFLP DNA mapping techniques 总被引:16,自引:0,他引:16
Jhy-Jhu Lin Jonathan Kuo Jin Ma James A. Saunders Hunter S. Beard Margaret H. MacDonald William Kenworthy George N. Ude Benjamin F. Matthews 《Plant Molecular Biology Reporter》1996,14(2):156-169
Three different DNA mapping techniques—RFLP, RAPD and AFLP—were used on identical soybean germplasm to compare their ability
to identify markers in the development of a genetic linkage map. Polymorphisms present in fourteen different soybean cultivars
were demonstrated using all three techniques. AFLP, a novel PCR-based technique, was able to identify multiple polymorphic
bands in a denaturing gel using 60 of 64 primer pairs tested. AFLP relies on primers designed in part on sequences for endonuclease
restriction sites and on three selective nucleotides. The 60 diagnostic primer pairs tested for AFLP analysis each distinguished
on average six polymorphic bands. Using specific primers designed for soybean fromEco RI andMse I restriction site sequences and three selective nucleotides, as many as 12 polymorphic bands per primer could be obtained
with AFLP techniques. Only 35% of the RAPD reactions identified a polymorphic band using the same soybean cultivars, and in
those positive reactions, typically only one or two polymorphic bands per gel were found. Identification of polymorphic bands
using RFLP techniques was the most cumbersome, because Southern blotting and probe hybridization were required. Over 50% of
the soybean RFLP probes examined failed to distinguish even a single polymorphic band, and the RFLP probes that did distinguish
polymorphic bands seldom identified more than one polymorphic band. We conclude that, among the three techniques tested, AFLP
is the most useful. 相似文献
85.
86.
B. Canguilhem A. Malan M. Masson-Pévet P. Nobelis R. Kirsch P. Pévet J. Le Minor 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1994,163(8):690-698
Temporal patterns of hibernation were studied by continuous monitoring of body temperature by radiotelemetry over 6 months in European hamsters, Cricetus cricetus, at constant temperature and photoperiod. Entrances into hibernation occurred mostly at the end of the night (0000–0800 hours), while arousals were randomly distributed between day and night. This is at variance with a control of bout duration by a clock with a period of 24 h. Consequently, the timing of entrances implies a phase-resetting of the circadian clock on each arousal. Persistence of circadian rhythmicity with a period different from 24 h during deep hibernation was investigated examining whether the durations of torpor bouts were integer multiples of a constant period. A non-parametric version of the classical contingency test of periodicity was developed for this purpose. Periods ranging from 21 to 29 h were tested. Nine animals out of ten showed at least one significant period in this range (P<0.01), either below 24 h (21.8±0.5 h, n=4) or above (27.3±0.5 h, n=7). However, we have found a theoretical model of bout durations for which the contingency test of periodicity sometimes gives false significant results. This indicates that the power of the test is weak. With this reservation our results suggest that a circadian oscillator controls the duration of a bout of hibernation, which would occur after an integer, but variable and possibly temperature-dependent number of cycles.Abbreviations b
a contingency test (see Appendix)
- SCN
suprachiasmatic nuclei
-
period
-
T
b
body temperature 相似文献
87.
Decay-accelerating factor CD55 is identified as the receptor for echovirus 7 using CELICS, a rapid immuno-focal cloning method. 总被引:14,自引:2,他引:12
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T Ward P A Pipkin N A Clarkson D M Stone P D Minor J W Almond 《The EMBO journal》1994,13(21):5070-5074
Using an anti-receptor mAb that blocks the attachment of echovirus 7 and related viruses (echoviruses 13, 21, 29 and 33), we have isolated a complementary DNA clone that encodes the human decay-accelerating factor (CD55). Mouse cells transfected with the CD55 clone bind echovirus 7, and this binding is blocked by the anti-receptor mAb. The method used (CELICS) allows rapid and direct cloning of genes encoding cell surface receptors. It is based on episomal replication and high efficiency expression of complementary DNA clones in the vector pCDM8 in COS or WOP cells, in conjunction with a sensitive immuno-focal screen that uses antibody probes linked to beta-galactosidase. Receptor positive cells were identified by a colour change and isolated individually using a micromanipulator. DNA extracted from a small number of cells was then cloned directly in Escherichia coli. 相似文献
88.
To study the mechanism of protein carboxyl methyltransferase-driven repair of age-damaged sites in polypeptides, a modell-isoaspartyl peptide,l-isotetragastrin, was enzymatically repaired to normall-tetragastrin in the presence of18O-enriched water. By this design, the enrichment of18O atoms in the peptide would reflect the number of passages through a hydrolyzable succinimide intermediate during formation of the repaired product. Mass determinations by FAB mass spectrometry revealed repaired peptide with two18O atoms incorporated, demonstrating that more than a single cycle of methylation and demethylation is necessary to ensure stoichiometric repair.Abbreviations HPLC
high-pressure liquid chromatography
- FAB
fast atom bombardment
- TFA
trifluoroacetic acid
- PCM
proteind-aspartyl/L-isoaspartyl carboxyl methyltransfer-ase
-
l-Normal
[l-Asp3]tetragastrin
-
l-Iso
[L-isoAsp3]tetragastrin
-
d-Normal
[d-Asp3]tetragastrin
-
d-Iso
[d-isoAsp3]tetragastrin 相似文献
89.
A question that is central to understanding the mechanisms of aging and cellular deterioration is whether enzymes involved in recognition and metabolism of spontaneously damaged proteins are themselves damaged, either becoming substrates for their own activity; or being unable to act upon themselves, initiating cascades of cellular damage. We show here byin vitro experiments that protein (d-aspartyl/l-isoaspartyl) carboxyl methyltransferase (PCM) from bovine erythrocytes does methylate age-dependent amino acid damage in its own sequence. The subpopulation that is methylated, termed thePCM fraction, appears to be formed through age-dependent deamidation of an asparaginyl site to either anl-isoaspartyl ord-aspartyl site because (a) the stoichiometry of automethylation of purified PCM is less than 1%, a value typical of the substoichiometric methylation of many other aged protein substrates, (b)PCM is slightly more acidic than the bulk of PCM, and (c) the methyl esterified site inPCM has the characteristic base-lability of this type of methyl ester. Also, the methyl group is not incorporated into the enzyme as an active site intermediate because the incorporated methyl group is not chased onto substrate protein. The effect of enzyme dilution on the rate of the automethylation reaction is consistent with methylation occurring between protein molecules, showing that the pool of PCM is autocatalytic even though individual molecules may not be. The automethylation and possible self-repair of the PCM pool has implications for maintaining thein vivo efficiency of methylation-dependent protein repair. 相似文献
90.