摘要:

AbstractSea urchins have elaborated multiple defenses to assure monospermic fertilization. In this work, we have concentrated on a study of the mechanism(s) by which hydrogen peroxide (H2O2) prevents polyspermy inArbacia punctulata. We found that it is not H2O2but probably hypochlorous acid/hypochlorite (HOCl/OCl−) derived from H2O2that is toxic to the supernumerary sperm. The spermicidal activity of H2O2is potentiated by at least one order of magnitude by cupric ions (Cu2+). This increased toxicity is not due to the formation of hydroxyl radicals (·OH) because ·OH scavengers did not counteract the activity of Cu2+. More‐over, substitution of Cu2+by ferrous ions (Fe2+), which are known to cause formation of ·OH from H2O2, had no effect on fertilization even at 102−103times higher concentrations. In contrast, 3‐amino‐1,2,4‐triazole (AT), an HOCl/OCl−scavenger, totally reversed the toxic effects of Cu2+. Furthermore, we found that HOCl/OCl−is generated in solutions of H2O2and Cu2+in the presence of 0.5 M NaCl and that its accumulation is abolished by AT. Thus it is possible that the antifertility properties of copper are due to its ability to mediate formation of HOCl/OCl−. HOCl/OCl−generated by Cu2+from H2O2and Cl−, a low concentration of exogenously added HOCl/OCl−, or increased concentrations of H2O2has similar inhibitory effects on the fertilization process in sea urchins. Therefore, we suggest that polyspermy is prevented by the action of a myeloperoxidase that affects the formation of HOCl/OCl−from the Cl−present in sea water through reaction with H2O2generat

ISSN:0730-2312    

DOI:10.1002/jcb.240300302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

Abstract3611 MSV, araf‐oncogene‐transducing murine retrovirus, induces fibrosarcomas and erythroid hyperplasia in newborn mice after a latency of 4–8 wk. In contrast, new recombinant murine retroviruses carrying themyconcogene (J‐3, J‐5 construct viruses) do not induce tumors before>9 wk. A combination of both oncogenes in an infectious murine retrovirus (J‐2) induces hematopoietic neoplasms in addition to less prominent fibrosarcomas and pancreatic adenocarcinoma 1–3 wk after inoculation. The hematologic neoplasms consist of immunoblastic lymphomas of T and B cell lineage and erythroblastosis. If animals were inoculated with a variant of the J‐3 virus, which induces altered foci in cultures of NIH 3T3 cells, carcinoma developed in the pancreas with a 2–6 mo latency. In parallel to the synergistic action of both oncogenes on hematopoietic cells in vivo, we find thatraf‐oncogene‐induced transformation of bone marrow cells in culture is enhanced by the addition ofmyc, which by itself does not transform these cells when grown in standard media. We conclude that concomitant expression ofrafandmyconcogenes in hematopoietic and epithelial cells alters their respective transforming activities. The contribution of v‐mycin this synergism was examined by use of a series of recombinant murine retroviruses capable of expressing the avian v‐mycto study the effect of alteredmycexpression on hematopoietic/lymphoid cells. With either interleukin 3‐ or interleukin 2‐dependent cell lines, introduction of the recombinant viruses abrogated the requirement for IL 3 or IL 2 for growth, and associated with this was the suppression of c‐mycexpression. The findings suggest thatmycis a component in the signal transduction pathway for IL 3 and IL 2 and support an autoregulatory mechanism of c‐mycexpression. In contrast to v‐myc, expression of v‐rafprimary lymphoid hematopoietic cells has an immortilizing function without abrogating the requirement for IL 3 for growth. This suggests that v‐rafand v‐mycaffect different components of growth regulation, as, for example, commitment (

ISSN:0730-2312    

DOI:10.1002/jcb.240300303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractAgonist treatment of C6‐glioma cells induces two altered states in β‐adrenergic receptors, a low affinity for the hydrophilic antagonist CGP‐12177 and a low affinity for agonists like isoproterenol. We present evidence that, in cells not treated to inhibit receptor internalization, the two properties occur with a different time course, the low affinity for isoproterenol preceding that for CGP‐12177. In that the low affinity for CGP‐12177 is due to the internalization of the receptor, the results indicate that uncoupling of the receptor, indicated by the low affinity for isoproterenol, occurs while the receptor is, still located on the cell surface. Removal of the agonist leads to reappearance of the receptor to the plasma membrane followed by loss of the uncou

ISSN:0730-2312    

DOI:10.1002/jcb.240300304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractWe have identified the three‐dimensional ultrastructure of actin gels that are formed in well‐characterized cell extracts and mixtures of purified actin and the 120K actin‐binding protein and compared these to the ultrastructure of the cytoplasmic matrix in regions of nonextractedDictyosteliumamoebae that are rich in actin and 120K. This ultrastructural characterization was achieved by using critical‐point‐dried whole‐mount preparations.All three preparations—gelled extracts, purified proteins, and cortical cytoplasm—are composed of filament networks. The basic morphological feature of these networks is the presence of contacts between convergent filaments resulting in “T” or “X” shaped contacts.The finding that actin‐containing gels are composed of filament networks, where the primary interaction occurs between convergent filaments, reconciles the known requirement of F actin for gelation with the amorphous appearance of these gels in thin sections.Increasing the molar ratio of 120K dimer to actin monomer increases the number of contacts between filaments per unit volume and decreases the lengths of filaments between contacts. This indicates that 120K stabilizes interactions between filaments and is consistent with biochemical evidence that 120K cross‐links actin filaments.The cortical network in situ resembles more closely networks formed in 120K‐rich extracts than networks assembled in mixtures of purified 120K and actin. The heterogeneity of filament diameters and variation of network density are properties shared by extracts and the cytomatrix in situ while networks found in purified l20K‐actin gels have filament diameters and densities that are more uniform. These differences are certainly due to the more complex composition of cell extracts and cortical cytoplasm as compared to t

ISSN:0730-2312    

DOI:10.1002/jcb.240300305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractSpectrin, the major component of the erythroid membrane skeleton, is a long, asymmetrical rodlike protein that interacts with several other proteins to form a two‐dimensional membrane skeleton. Progress in several laboratories over the past few years including substantial partial peptide and nucleotide sequence determination has greatly enhanced our knowledge of the structrual properties of this large molecule (heterodimer = 465,000 daltons). The alpha and beta subunits are homologous with approximately 30% identity. They are aligned in an anti‐parallel side‐to‐side orientation with the amino‐ and carboxy‐termini near opposite physical ends of the molecule. The predominant structural feature elucidated from sequencing this large molecule is the nearly universal occurrence in both subunits of a single type of repetitive structure. The periodicity of this homologous structure is exactly 106 amino acid residues. As many as 36 homologous, but non‐identical, repeats exist and comprise more than 90% of the mass of the heterodimer. Each of these repetitive units is folded into a triple‐stranded structure that is highly helical. Peptide maps, antibody cross‐reactivity, peptide sequence analysis, and more recently nucleic acid sequences have defined several major properties of the erythroid molecule and related proteins in other tissues. Tissue‐specific spectrins have the same 106‐residue repetitive structure and show sequence homology

ISSN:0730-2312    

DOI:10.1002/jcb.240300306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractTalin is a 225,000‐Dalton protein we have purified from smooth muscle. In chick embryo fibroblasts talin is found in adhesion plaques (focal contacts), areas where the cell is closely opposed to the substratum. In comparison with other cytoskeletal proteins, we found talin to be unusually susceptible to proteolysis and have identified a 190,000‐Dalton proteolytic fragment of talin in the immunoblots of many tissues. These observations raised the possibility that the cleavage of talin to this fragment has physiological relevance. One system that we have investigated in which significant proteolysis occurs is platelets. During platelet activation several high‐molecular‐weight proteins are cleaved to lower‐molecular‐weight forms. Here we demonstrate that talin is closely related to one of these platelet high‐molecular‐weight proteins, P235. The purification of talin is comparable to that developed for P235, and the two proteins have similar biophysical properties. In addition, antibodies raised against chicken gizzard talin recognize P235 in purified form as well as in crude platelet extracts. The platelet protein also resembles smooth‐muscle talin in its susceptibility to endogenous proteolysis: P235 is rapidly cleaved to a 190‐200kD polypeptide by a calcium‐activated protease found in platelet extracts. Moreover, partial proteolysis of P235 and talin with chymotrypsin, elastase, or trypsin also generates remarkably similar one‐dimensional peptide maps. Because of their similar biophysical properties, immunological crossreactivity, and similar one‐dimensional partial peptide maps, we conclude that P235 is t

ISSN:0730-2312    

DOI:10.1002/jcb.240300307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractA complex of calmodulin (CM) and the 110‐kD (110K) subunit composes the helical array of cross‐bridges linking the microvillus actin filament bundle with the membrane. The hydrophobic properties of the 110K protein, assessed by the detergent phase partitioning assay [Bordier C: J Biol Chem 256:1604, 1981], are highly dependent on the solution conditions used in its isolation. The ATP‐dissociable 110K‐CM complex [Howe and Mooseker: J Cell Biol 97:974, 1983]exhibits hydrophilic characteristics in this assay. In contrast, the 110K subunit extracted from brush borders by Triton X‐100, sodium dodecyl sulfate, and sodium pyrophosphate (detergent‐treated 110K) [Glenney JR, Glenney P: Cell 37:743, 1984] behaves as a hydrophobic protein. However, because the soluble hydrophilic 110K‐CM can be rendered hydrophobic by treating the complex with the same detergent and salt conditions used in the preparation of detergent‐treated 110K, the properties of detergent‐treated 110K seem likely to be an effect of the solution conditions on its native conformation, sedimentability, or exposure of binding domains. In addition, the detergent‐treated 110K is devoid of calmodulin and no longer exhibits the actin‐binding activity characteristic of the ATP‐dissociable 110K‐CM and of the intact complex in situ. With two partially purified preparations of the 110K subunit exhibiting such dramatically distinct properties, it seems premature to define the nature of the 110K subunit's association with

ISSN:0730-2312    

DOI:10.1002/jcb.240300308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240300301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY