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1. The amino acid composition of highly purified aspartate aminotransferase from ox heart was determined. 2. Alanine is the only N-terminal residue. 3. Leucine was identified as the only C-terminal residue. 4. No disulphide bridges are present in the enzyme molecule. 5. The thiol groups are not equally accessible, the accessibility being comparatively easier in the apoenzyme molecule. 相似文献
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Norepinephrine stimulates the growth in size of non-dividing, neonatal cardiac muscle cells, and it can stimulate the growth in numbers of dividing hepatocytes and endothelial cells in culture. The objective of this study was to test the hypothesis that in dividing fetal cardiocytes, norepinephrine would stimulate growth in cell number rather than in cell size. Fourteen-day fetal heart cells were placed in serum-free or serum-supplemented cultures in the presence or absence of norepinephrine (NE), NE plus propranolol, or isoproterenol for 4 days. Almost 90% of the cardiocytes in serum-supplemented medium were in the cell cycle as determined by proliferating cell nuclear antigen (PCNA) antibody staining during this period. In addition, between days 2 and 4 of culture, 35% and 40% of these cardiocytes were labeled with 3H-thymidine. After 4 days the cardiocytes increased in cell number in the serum-supplemented NE cultures as compared to serum-free cultures. In contrast, there was no significant change in cardiocyte volume between any of the groups examined. It was concluded that in dividing muscle cell populations the effect of norepinephrine was to enhance cell proliferation rather than to stimulate cell growth in size. 相似文献
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Chymotrypsin-like enzymes are involved in sperm penetration through the vitelline coat of Ciona intestinalis egg 总被引:2,自引:0,他引:2
M R Pinto M Hoshi R Marino A Amoroso R De Santis 《Molecular reproduction and development》1990,26(4):319-323
In Ciona intestinalis, sperm penetration through the egg vitelline coat is an essential event of fertilization. We investigated whether trypsin- and chymotrypsin-like enzymes are involved in this event. Inhibitors and peptide substrates for chymotrypsin-like enzymes blocked the overall process of fertilization in a concentration-dependent manner. The inhibitory activity was specifically exerted on the step of sperm penetration. Chymotrypsin-like protease activity was identified in spermatozoa with the fluorogenic synthetic substrate Suc-Ala-Ala-Phe-AMC, which was the most effective substrate in blocking sperm penetration. These data indicate that a chymotrypsin-like protease activity is a sperm lysin of Ciona intestinalis. 相似文献
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Marcello Franco Eduardo Bagagli Marino Cunha Luiz Gastão Chamma Denise Fecchio 《Mycopathologia》1996,135(1):13-19
We investigated the occurrence of antigenic and biochemical variability among Paracoccidioides brasiliensis antigen batches prepared according to the same protocol. Initially (experiment #1), we analyzed two antigen lots of two human isolates (Bt1 & Bt2), cultured in two media (PYG: bactopeptone, yeast extract, glucose; MMM: McVeigh & Morton medium) in SDS-PAGE and in two immunological tests (imunodiffusion-ID and footpad swelling test-FPT). Afterwards (experiment #2), we compared the antigenic profile of three antigen batches from three human isolates (Bt1, Bt2 & Bt3) by two-dimensional immunoelectrophoresis (2 D-IEP) against a reference system for P. brasiliensis antigens. In experiment #1, there were important intra- and inter-strain antigenic differences between batches of the fungal isolates cultured on both media. The block titration of the antigen batches for the immunological tests revealed correlation between protein concentration and biological activity in ID and no correlation in FPT. In experiment #2, the reference system for P. brasiliensis showed 26 antigen peaks. There were important differences between batches prepared from the same isolate and between batches from different isolates. Our data suggested the occurrence of instability in the synthesis of antigenic components by a same P. brasiliensis isolate, under controlled incubation conditions. 相似文献
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S. Leoni S. Spagnuolo M. Marino F. Terenzi M. Massimi L. Conti Devirgiliis 《Journal of cellular physiology》1993,155(3):549-555
[1-14C]-2-aminoisobutyric acid (AIB) uptake and signal transduction pattern after epidermal growth factor (EGF) stimulation were examined in freshly isolated hepatocytes from 20-day-old fetuses and 3-month-old rats. EGF induced a transient increase of AIB transport after 10 min only in adult animals; the observed unresponsiveness of fetal liver is not dependent on a lack of EGF receptors which are present though to a lesser extent on the plasma membrane in this period. As far as the production of the second messengers, inositol trisphosphate (IP3) and calcium, is concerned, substantial differences were found: EGF increased IP3 production in adult hepatocytes, whereas it had no effect in fetal ones. Moreover, the addition of EGF induced a calcium transient in hepatocytes from adult animals, while there was no increase in fetal cells. The lack of EGF effect on amino acid transport in fetal cells could be due to its inability to produce both IP3 and calcium transients, suggesting that this transduction pathway is not activated during fetal life. 相似文献
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While investigating dinoflagellate cyst assemblages in surface sediments of the Gulfs of Naples and Salerno (Mediterranean Sea), we found a new calcareous resting cyst. This cyst has a round to oval body surrounded by a thick mineral layer, which gives it the shape of a Napoleon hat, with a flat, oval face bearing the archeopyle and a convex keel on the opposite side. The cyst shape is variable in both natural samples and clonal cultures. The organic membrane underlying the calcareous covering is resistant to acetolysis, thus demonstrating the presence of sporopolleninlike material. The cyst germinated into a motile stage having the same morphological features and thecal plate pattern as Peridinium tyrrhenicum Balech. We believe the validity of the genus Pentapharsodinium Indelicato & Loeblich should be accepted. Based on the comparative examination of the species we collected and of a similar species, Pentapharsodinium trachodium Indelicato & Loeblich, we propose Pentapharsodinium tyrrhenicum as a new combination for Peridinium tyrrhenicum. The genus Pentapharsodinium also includes P. dalei Indelicato & Loeblich (= Peridinium faeroense Dale), which produces spiny, organic-walled cysts. The presence of species forming calcareous cysts and species producing noncalcareous cysts in the same genus raises questions about maintaining the family Calciodinellaceae. This family should only include calcareous cyst-forming peridinioids, in order to maintain a unified system of classification of fossil and recent dinoflagellates. 相似文献