Navegando por Palavras-chave "MEMBRANE"

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    BINDING of SEX-HORMONE-BINDING GLOBULIN (SHBG) TO TESTICULAR MEMBRANES and SOLUBILIZED RECEPTORS
    (Elsevier B.V., 1992-11-01) Porto, C. S.; Abreu, L. C.; Gunsalus, G. L.; Bardin, C. W.; POPULAT COUNCIL; Universidade Federal de São Paulo (UNIFESP)
    Sex-hormone-binding globulin (SHBG) binds to a specific protein on the surface of prostate, epididymis, and a human breast cancer cell line (MCF-7), and is internalized by these cells. the present study demonstrated specific binding of SHBG to receptor on membranes prepared from rat testes. the binding was saturable, specific, and time and temperature dependent. Scatchard analysis of these binding studies suggested that SHBG binds to a single class of sites on testicular membranes with a K(d) at 37-degrees-C of 5 X 10(-8) M and a binding capacity of 30 +/- 0.6 pmol/mg protein. These binding characteristics are similar to the SHBG receptor on human prostate and MCF-7 cells. Solubilization of the receptor resulted in a 5-fold increase in its binding capacity (158 +/- 0.3 pmol/mg protein) and a 10-fold decrease in binding affinity (K(d) at 37-degrees-C = 6.5 X 10(-7) M). the apparent molecular weight of the testicular SHBG receptor, as estimated by gel filtration, was M(r) = 174,000. Conclusion: a specific binding site for SHBG was identified on testicular membranes. This binding site has been tentatively identified as a SHBG receptor based on its physical properties in testicular membrane preparations and following solubilization.
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    HELA-CELLS EXTEND AND INTERNALIZE PSEUDOPODIA DURING ACTIVE INVASION BY TRYPANOSOMA-CRUZI TRYPOMASTIGOTES
    (Company Of Biologists Ltd, 1992-04-01) Schenkman, Sergio [UNIFESP]; Mortara, R. A.; Universidade Federal de São Paulo (UNIFESP)
    We show here that HeLa cell microfilaments can be stained by phatloidin at the sites of invasion of Trypanosoma cruzi trypomastigotes, one of the infective stages of this protozoan parasite. Concurrently, a projection of the HeLa cell plasmalemma encircles invading parasites. This plasmalemma projection is further internalized and entire membrane protrusions containing parasites are found within cytoplasmic vacuoles of the host cell. Neither the microfilament staining around invading parasites nor the plasma-lemma extension is inhibited by cytochalasin D, a drug that is unable to prevent trypomastigote entry into HeLa cells. The internalization of the membrane expansion, however, is blocked by the drug. These novel observations indicate that although the driving force for T. cruzi penetration comes from the parasite, the cortical target cytoskeleton of the target cell is concomitantly modified. The molecular characterization of this phenomenon may provide a new insight into the understanding of the mechanisms involved in the active penetration of T. cruzi into mammalian cells.