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91.
92.
We have modelled a phospholipid bilayer as two monolayer sheets which interact with each other by a coupling which depends upon the states of the lipid hydrocarbon chains in each sheet. We make use of a model (Georgallas and Pink 1982a) and its parameters, already used to study monolayer phase changes at the LC-LE transition, in order to study the lipid main transition. Although the monolayer coexistence curve can be calculated exactly, we have made use of high-temperature series expansions to calculate the critical point of the bilayer. We also present the results of computer simulations on triangular lattices for the pressure-area isotherms. We find: (i) the interaction between the sheets of a DPPC bilayer is about 1.5–2% of the maximum interaction within the plane of each sheet; (ii) the internal lateral pressure of a DPPC bilayer is about 30.5 dyne/cm; (iii) the bilayer transition enthalpy depends sensitively upon the coupling between the sheets. Should this coupling vary from sample to sample (due, possibly, to its preparation) then very different values of transition enthalpy may be measured. (iv) We present a rough rule-of-thumb for estimating the internal lateral pressure of a bilayer from a knowledge of the corresponding monolayer pressure-area isotherms.Abbreviations LC-LE liquid condensed — liquid expanded - DPPC dipalmitoylphosphatidylcholine - Q transition enthalpy Work supported in part by the Natural Sciences and Engineering Research Council of Canada  相似文献   
93.
Synthesis of collagen and proteoglycan by rabbit articular chondrocytes and synovial fibroblasts has been studied over a 12-week period in primary monolayer culture. Chondrocytes, but not fibroblasts, accumulate large quantities of proteoglycan over the culture period studied. Radiolabeling studies with [35S]sulfate have shown that the major proteoglycan synthesized by cultured chondrocytes is similar to the proteoglycan of cartilage matrix. Chondrocytes also synthesize a smaller dermatan sulfate proteoglycan, which is apparently the only proteoglycan species produced by synovial fibroblasts. Collagen synthesis was studied by radiolabeling with [3H]proline. Cultured chondrocytes produce mainly Type II collagen, with lesser amounts of Type I, whereas synovial fibroblasts produce Type I collagen and some low molecular weight collagenous species. Therefore, long-term monolayer culture permits the production of extensive chondroid matrix by chondrocytes, but not fibroblasts.  相似文献   
94.
The LSTRA murine thymoma cell line contains an elevated level of tyrosine protein kinase activity. When a microsomal preparation from these cells is incubated in vitro with ATP, the principal tyrosine protein kinase substrate is a 56,000-dalton protein, p56. We have found that an activity phosphorylating p56 on tyrosine can also be detected at low levels in microsomes from most, but not all, T lymphoma cell lines and from normal thymic tissue. Only 1 of 30 other lymphoma cell lines was found to contain an elevated level of such a tyrosine protein kinase. An activity that phosphorylated p56 in vitro was not detectable in the cells of other hematopoietic lineages. Anti-peptide antibodies reactive with the site of in vitro tyrosine phosphorylation of p56 allowed us to determine that the apparent abundance of the p56 polypeptide parallels closely the level of the tyrosine protein kinase activity in the cell lines examined. This suggests that p56 is the protein kinase responsible for the elevated tyrosine protein kinase activity in LSTRA cells and that the phosphorylation of p56 observed in vitro results from autophosphorylation. Two-dimensional tryptic peptide mapping revealed that p56 is distinct from the proteins encoded by the cellular genes which are the progenitors of retroviral tyrosine protein kinases, src, yes, fgr, abl, fes, and ros. Additionally, none of these proto-oncogenes was found to be transcribed at elevated levels in LSTRA or Thy19 cells. Like the catalytic subunit of the cyclic AMP-dependent protein kinase, the cellular and viral forms of p60src, and the protein phosphatase calcineurin B, p56 contains covalently bound fatty acid.  相似文献   
95.
Summary Intratumor injections of the aqueous phase of phenol-water extracts of Re mutant Salmonella typhimurium (Re glycolipid) in combination with trehalose dimycolate at dose levels of 150 to 15 g were consistently and highly effective (65–93%) in producing regression of line-10 tumors in strain-2 guinea pigs. We observed that the rate of regression was more rapid than that seen after treatment with cell walls from Mycobacterium bovis strain Bacillus of Calmette and Guèrin (BCG). Arabinose mycolate could be substituted for trehalose dimycolate in the Re glycolipid-mycolate mixture without appreciably compromising antitumor activity, providing that the level of arabinose mycolate was not reduced below 15 g. In addition to the Re glycolipid preparation, similarly prepared aqueous extracts from Mycobacterium bovis strain BCG and strain AN5 in combination with trehalose dimycolate also possessed tumor-regressive activity. The activity of these last extracts was reduced when the arabinose mycolate was substituted for the trehalose dimycolate. The aqueous extract of a rickettsia, Coxiella burnetii, in combination with either trehalose dimycolate or arabinose mycolate was also active (50 and 80% tumor regression rates, respectively). Intracutaneous administration of Re glycolipid or aqueous extracts from BCG in combination with trehalose or arabinose mycolates did not produce life-threatening, clinical signs of toxicity in young mice. If additional toxicity studies demonstrate that adverse side effects can be satisfactorily controlled, these watersoluble extracts may prove beneficial in the treatment of spontaneous tumors of humans and other animals.  相似文献   
96.
Summary We made a comparative study of the in vivo binding of immunoglobulins (Ig) to a polyoma virus-induced ascitic tumor propagated in syngeneic or allogeneic mice. The Ig coat was found to appear more rapidly and to be denser in H 2-incompatible than in H 2-compatible mice. This suggests that antibodies were fixed specifically on strong normal transplantation antigens (H-2) recognized as non-self by allogeneic mice. Experiments with mice in which immunosuppression had been achieved by means of X-irradiation confirmed that the Ig fixed on SEWA cells are actively bound antibodies. The only mice that could fix Ig on tumor cells were those that had been specifically immunized against cell surface antigens shared by SEWA cells before irradiation, while mice hyperimmunized against nonrelated antigens could not.In partial fulfilment of doctorate thesis requirements  相似文献   
97.
Earlier we reported on the presence of a specific phenolic glycolipid (Phenolic Glycolipid-I) in Mycobacterium leprae, and in infected armadillo tissues (Hunter, S. W., and Brennan, P. J. (1981) J. Bacteriol. 147, 728-735). It had an inherent oligosaccharide, composed of 3-O-Me-rhamnose, 2,3-di-O-Me-rhamnose, and 3,6-di-O-Me-glucose, glycosidically linked to the phenol substituent. The structure of the oligosaccharide has now been determined, by partial acid hydrolysis, permethylation, 1H NMR, and 13C NMR as: 3,6-di-O-Me-Glcp(1 beta leads to 4)2,3-di-O-Me-Rhap(1 alpha leads to 2)3-O-Me-Rhap1 alpha leads to phenol (assuming that the glucose substituent is in the D-enantiomeric configuration, and the two methylated rhamnoses are L). Acid hydrolysis of deacylated Phenolic glycolipid-I yielded a phenolic phthiocerol "core," and mass spectrometry and proton NMR of the permethylated core suggested the following structure: (formula, see text) Combined gas-liquid chromatography-mass spectrometry showed three tetramethyl branched "mycocerosic" acids, C30, C32 and C34, with molecular weights (as methyl esters) of 466, 494, and 522, respectively. These are esterified to the hydroxyl functions of the branched glycolic chain. Evidence is also presented that the glycolipid is immunologically active, reacting with rabbit antisera to M. leprae and with sera from lepromatous leprosy patients.  相似文献   
98.
J Papkoff  I M Verma  T Hunter 《Cell》1982,29(2):417-426
We identified, in cells transformed by Moloney murine sarcoma virus (M-MuSV clone 124), a protein encoded by the M-MuSV transforming gene, v-mos. An antiserum against a synthetic peptide corresponding to the C terminus of a protein predicted from the v-mos nucleotide sequence specifically recognizes a protein doublet of approximately 37,000 daltons from 35S-methionine-labeled M-MuSV 124-transformed producer cells. By peptide mapping, this protein is almost identical to the 37 kd in vitro translation product from the M-MuSV v-mos gene. Immunoprecipitates from 32P-labeled cells contain a single v-mos-specific phosphoprotein, which has at least six sites of phosphorylation containing phosphoserine. Pulse-chase experiments show that the lower band in the 35S-methionine-labeled doublet is the primary translation product, which is modified, probably by phosphorylation, to yield the upper band. A similar mos protein is immunoprecipitated from HT1-MuSV-transformed cells, but not from uninfected NIH/3T3 cells. These mos proteins are present at very low levels in transformed cell lines. Cells acutely infected with M-MuSV 124, however, transiently contain much higher levels of the mos protein. These high levels coincide with extensive cell mortality.  相似文献   
99.
Platelet-derived growth factor (PDGF) stimulates the phosphorylation of proteins at tyrosine when added to quiescent 3T3 cells, as evidenced by the increase in the amount of phosphotyrosine, relative to phosphoserine and phosphothreonine, in cellular proteins. The increase was detected within 1 min of adding PDGF and was maximal by 5 min. This effect showed the same dependence on PDGF concentration as did association of 125I-PDGF with the cells. In different 3T3 cell lines the magnitude of the increase was approximately proportional to the number of PDGF receptors per cell. A number of proteins phosphorylated at tyrosine in response to PDGF have been detected by two-dimensional gel electrophoresis. They include a pair of related 45 kilodalton phosphoproteins, a pair of related 43 kilodalton phosphoproteins and a 42 kilodalton phosphoprotein. Similar changes were noted when quiescent 3T3 cells were incubated with epidermal growth factor. Possibly, these phosphoproteins are primary substrates of the tyrosine protein kinases activated by the receptors for PDGF and epidermal growth factor, and are involved in physiological effects common to the two growth factors.  相似文献   
100.
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