摘要:

AbstractThe T‐lymphocyte activation process involves a series of coordinately coupled biochemical events occuring in response to antigen or mitogen. These events have not been completely characterized. The present studies investigate the mechanism of protein synthesis during the initial phase of T‐cell activation. Among the early biochemical changes, induction of protein synthesis was observed as early as 10 minutes after mitogen stimulation of T‐lymphocytes. This early protein synthesis was inhibited by cycloheximide but was insensitive to actinomycin‐D, indicating the presence of preformed mRNA in resting lymphocytes. Since early protein synthesis parallels the increase in protein kinase C activity in activated T‐lymphocytes, these two biochemical events may be related. In the present report, amiloride, an inhibitor of Na+/H+antiport and protein kinase C, significantly inhibited [3H‐]leucine and [3H‐]thymidine incorporation in a dose‐dependent manner into phytohemagglutinin (PHA)‐stimulated T‐lymphocytes. Furthermore, when T‐lymphocytes were stimulated by phorbol myristate acetate, a known activator of protein kinase C, a similar inhibition of protein and DNA synthesis by amiloride was observed. The partially purified cytosol fraction isolated from PHA‐activated T‐lymphocytes showed a 75% decrease in protein kinase C‐mediated [32P] incorporation from ATP in the presence of 100 μM amiloride. These results suggest that the T‐cell activation process following exposure to mitogens involves early protein synthesis, which may b

ISSN:0730-2312    

DOI:10.1002/jcb.240330302

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

年代:1987

数据来源: WILEY

摘要:

AbstractATP‐dependent protein kinase activities were detected in both membrane and cytoplasmic fractions from the oral pathogenStreptococcus mutans. Different polypeptides were phosphorylated by endogenous kinase(s) in the two fractions. In membranes, five phosphoproteins were detected with apparent masses of 82, 37, 22, 12, and 10 kilodaltons (KD). In cytoplasm, two major acid‐stable phosphoproteins were found. One was identified as HPr of the, phosphoenolpyruvate (PEP)‐dependent phosphotransferase system (PTS), while the other had an apparent mass of 61 KD. Both of these proteins were phosphorylated on a seryl residue. Fructose 1,6‐bisphosphate stimulated phosphorylation of HPr by the kinase and inhibited phosphorylation of the 61‐KD protein. In contrast, fructose 1‐phosphate, 2‐phosphoglycerate, 3‐phosphoglycerate, and dihydroxyacetone phosphate inhibited phosphorylation of HPr and stimulated phosphorylation of the 61‐KD protein. Several other glycolytic intermediates as well as inorganic phosphate inhibited phosphorylation of either or both proteins. Preincubation of cytoplasm with PEP prior to incubation with ATP reduced the amount of phospho‐(seryl)‐HPr formed, but not that of the 61‐KD phosphoprotein. The latter protein has not yet been identified but has properties that suggest that it may be the protein kinase itself. These results provide evidence for one or more soluble ATP‐dependent protein kinases inS mutansthat are regulated by glycolytic intermediates and that may play a role in the modulation of carbohydrate uptake and metabolism in this organism. A model for feedback regulation of sugar transport inS mutans, mediated by an allosterically regu

ISSN:0730-2312    

DOI:10.1002/jcb.240330303

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

年代:1987

数据来源: WILEY

摘要:

AbstractHyaluronate‐binding protein (HASP) has been extracted in detergent from the membranes of simian virus 40‐transformed 3T3 (SV‐3T3) cells (Underhill et al, J Biol Chem 258:8086–8091, 1983). When SV‐3T3 cells were treated with trypsin prior to isolation and dissolution of the membranes, no hyaluronate‐binding activity could be detected. This indicates that all of the detectable HABP of SV‐3T3 cells is located on the external surface of the plasma membrane rather than on internal membranes, which would be inaccessible to the trypsin. The detergent‐extracted HABP from SV‐3T3 membranes was reconstituted into the membrane of lipid vesicles, which were formed by addition of exogenous phosphatidylcholine and cholic acid to the extracts followed by removal of detergent by dialysis against 0.02 M Tris pH 8.0 in the presence of protease inhibitors. Reconstitution was assessed by sedimentation in a discontinuous sucrose gradient and by gel filtration on Sepharose 4B in the presence and absence of detergent. The characteristics of binding of hyaluronate to the reconstituted HABP were then compared with those studied previously for the original membrane‐bound HABP and the detergent‐extracted HABP (Underhill et al, J Biol Chem 258:8086–8091, 1983). It was observed previously that binding of hyaluronate to HABP in the cell membranes was of higher affinity and specificity than to HABP in the detergent extracts of these membranes. It was found here that reconstitution of the extracted HABP into the membranes of lipid vesicles led to restoration of affinity of binding to the level observed in the original cell membranes. However, whereas chondroitin sulfate does not compete significantly for binding of hyaluronate to cell membrane‐bound HABP, partial competition was observed for the reconstituted HABP as well as for detergent‐extracted HABP. Thus, it is concluded that the high affinity of binding of hyaluronate to the plasma membrane of SV‐3T3 cells is in part dependent on insertion of the HABP in the membrane, but that other interactions, not duplicated in our reconstitution experiments, must be necessary fo

ISSN:0730-2312    

DOI:10.1002/jcb.240330304

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

年代:1987

数据来源: WILEY

摘要:

AbstractHuman protein C is a vitamin K‐dependent plasma protein that serves as a feedback down‐regulator of the coagulation cascade by specifically degrading the protein cofactors VIIIa and Va. The protein C precursor consists of the following domains: leader peptide, “gla” region, two epidermal growth factor segments, and the activation peptide/serine protease. Comparison of amino acid sequences reveals that protein C and factor IX are homologous. A comparison of the genes for protein C and factor IX shows that all seven of the introns within the protein coding regions are in identical positions and correspond to protein structure‐function domain boundries. However, the base compositions of the two genes (coding and noncoding regions) are remarkably different: ∼60% guanine + cytosine (G + C) for protein C versus ∼40% G + C for factor IX. One possible explanation for this phenomenon is that the factor IX gene (located on the X chromosome) has undergone extensive deoxycytosine methylation and subsequent spontaneous deamination mutagenesis, resulting in a net C to thymine (and G to adenine) transition. This would suggest that the protein C gene may represent a more primitive form of the gene duplicat

ISSN:0730-2312    

DOI:10.1002/jcb.240330305

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

年代:1987

数据来源: WILEY

摘要:

AbstractMature picornaviral proteins are derived by progressive, post‐translational cleavage of a giant precursor polyprotein. At least three viral‐encoded proteolytic activities are involved in the processing. The first cleavage takes place while the polyprotein is still nascent on a ribosome. In poliovirus, this event is probably catalyzed by peptide 2A, a protein from the middle portion of the genome. Most subsequent processing is effected by viral protease 3C, a thiol‐type enzyme, responsible for eight to ten self‐cleaving and autocatalytic reactions within the polyprotein. The final proteolytic processing event, maturation of the VPO peptide, may occur by a novel, autocatalytic, serine‐type mechanism, where viral RNA serves as proton‐acceptor during the cleava

ISSN:0730-2312    

DOI:10.1002/jcb.240330306

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

年代:1987

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240330307

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

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper presents evidence that the full repertoire of cellular genes involved in the carcinogenic process is several times larger than that of the known list of proto‐oncogenes. Furthermore, this repertoire includes genes whose normal function is related to growth stimulation, as well as genes whose normal function is to inhibit growth or induce terminal differentiation. Multistage carcinogenesis probably results from a complex series of changes in both categories of genes. Despite this complexity, carcinogenesis can be conceived in terms of disturbances in biochemical functions that normally control the expression or function of growth factors, receptors, and pathways of signal transduction. Several protein kinases play a central role in the process of signal transduction. Our laboratory has recently isolated cDNA clones for the enzyme protein kinase C (PKC). These clones should be useful for clarifying the role of PKC in growth control and tumor promotion. Finally, the existence of genes whose normal function is to inhibit cell growth provides a rationale for new strategies of cancer prevention and treatmen

ISSN:0730-2312    

DOI:10.1002/jcb.240330308

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

年代:1987

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240330301

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

年代:1987

数据来源: WILEY