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PubMed1996

On the failure of de novo-designed peptides as biocatalysts.

While the elegance and efficiency of enzymatic catalysis have long tempted chemists and biochemists with reductionist leanings to try to mimic the functions of natural enzymes in much smaller peptides, such efforts have only rarely produced catalysts with biologically interesting properties. However, the advent of genetic engineering and hybridoma technology and the discovery of catalytic RNA have led to new and very promising alternative means of biocatalyst development. Synthetic chemists have also had some success in creating nonpeptide catalysts with certain enzyme-like characteristics, although their rates and specificities are generally much poorer than those exhibited by the best novel biocatalysts based on natural structures. A comparison of the various approaches from theoretical and practical viewpoints is presented. It is suggested that, given our current level of understanding, the most fruitful methods may incorporate both iterative selection strategies and rationally chosen small perturbations, superimposed on frameworks designed by nature.

Catalysis↗

PubMed1996

Prostatic cell lineage markers: emergence of BCL2+ cells of human prostate cancer xenograft LuCaP 23 following castration.

A model of prostate cancer progression based on the expression pattern of informative genes in the human prostate cancer xenograft LuCaP 23.1 is presented. Apparently, there are at least 2 tumor cell populations of LuCaP 23.1, representing 2 different phenotypes. One is NSE (neuron-specific enolase)-positive and the other NSE-negative. NSE-positive tumors were recovered after hormone-independent growth in castrated mice. These hormone-independent tumors also expressed BCL2, a gene product shown to inhibit apoptosis. With NSE, BCL2 and PSA (prostate-specific antigen) as identifying markers, the model specifies a putative progression sequence of the prostate cancer cell types. We also show a proposed lineage relationship among the 3 principal normal cell types found in the prostatic epithelium.

Animals↗

PubMed1983

IgE-mediated release of leukotriene C4, chondroitin sulfate E proteoglycan, beta-hexosaminidase, and histamine from cultured bone marrow-derived mouse mast cells.

Mouse bone marrow-derived mast cells differentiated in vitro and sensitized with monoclonal IgE respond to antigen-initiated activation with the release of histamine, beta-hexosaminidase, chondroitin sulfate E proteoglycan, and leukotriene C4 (LTC4). The chondroitin sulfate E nature of the glycosaminoglycan side chain was established by demonstrating that the chondroitinase ABC disaccharide digestion products were composed of equal quantities of 4-sulfated and 4,6-disulfated N-acetyl-galactosamine. The single immunoreactive sulfidopeptide leukotriene, released and quantitated with a class-specific antibody, was identified as LTC4 by its retention time on reverse-phase high-performance liquid chromatography and by its specific spasmogenic activity on the guinea pig ileum. The release of the preformed mediators, as well as of LTC4, was related in a dose-response fashion to the concentration of monoclonal IgE used during the sensitization step and to the concentration of specific antigen used to initiate the activation-secretion response. The optimal concentrations of IgE for sensitization and of antigen for challenge were the same for the release of preformed mediators and of LTC4. In addition, the time courses of their release were superimposable, with a plateau at 5 min after antigen challenge. The release of three preformed mediators and of LTC4 after fixation of IgE, washing of the sensitized cells, and antigen challenge unequivocally indicates a bone marrow-derived mast cell origin for these products. Linear regression analyses of the net percent release of beta-hexosaminidase to histamine and of 35S-chondroitin sulfate E to beta-hexosaminidase yielded straight lines that intersected at the origin, which indicates that the three preformed mediators are localized in the secretory granules of the bone marrow-derived mast cells. The concomitant generation of 23 ng of LTC4/10(6) sensitized bone marrow-derived mast cells represents the first example of IgE-dependent release of substantial amounts of LTC4, a component of slow reacting substance of anaphylaxis, from a mast cell population of greater than 95% purity. The IgE-dependent generation of LTC4, rather than prostaglandin D2, by the chondroitin sulfate E proteoglycan-containing bone marrow-derived mast cells contrasts with the predominant generation of prostaglandin D2 by heparin proteoglycan-containing mast cells. These differences together support the existence of two phenotypically different mast cell subclasses.

Animals↗