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M Hoffman

Publications and source records attributed to M Hoffman.

At least 19 recordsLinked to original sources
PubMed1992

Coagulation factor IXa binding to activated platelets and platelet-derived microparticles: a flow cytometric study.

Factor IX plays a central role in blood coagulation, since it can be activated by either XIa (intrinsic pathway) or tissue factor-VIIa (extrinsic pathway). Activated factor IX (IXa), in a surface-bound complex with factor VIIIa, then activates factor X. Platelets provide the catalytic surface upon which this Xase complex is assembled in vivo. We have used flow cytometry to examine binding of factor IXa to thrombin-activated platelets in the absence of added VIIIa. Platelet-bound IXa and platelet protein GPIb were detected by indirect immunofluorescence staining followed by two-color flow cytometric analysis. Microparticles were identified by their light scattering characteristics. Two binding sites for factor IXa were detected. The high affinity binding site saturated at about 10 nM, with a Kd of 1.6 nM. A second binding curve, with a Kd of about 100 nM, was observed at higher concentrations of IXa. The high affinity factor IXa binding sites comprise about 7% of the total factor IXa binding. Binding to both sites was dependent on the presence of calcium. Thus, we conclude that factor IXa, in addition to its high affinity binding, has a calcium-dependent low affinity association with activated platelets and microparticles. Sims et al, have shown that binding sites for a different coagulation factor, factor Va, are concentrated on microparticles relative to platelet membrane proteins, such as GPIb. GPIb is distributed on platelets and microparticle in proportion to plasma membrane surface.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Platelets↗
PubMed1992

Stimulation of 5-fluorouracil metabolic activation by interferon-alpha in human colon carcinoma cells.

Interferon-alpha (IFN alpha) increases the cytotoxicity of 5-fluorouracil (FUra) in vitro, and the combination has clinical efficacy against advanced colorectal cancer. IFN alpha treatment of HT-29 colon carcinoma cells induced a greater than two-fold increase in the intracellular levels of the active metabolite of FUra, FdUMP. Using cell extracts from HT-29 cells and FUra as substrate, IFN alpha produced a 1.9- and 8.7-fold increase, respectively, in the activities of uridine phosphorylase and pyrimidine nucleoside phosphorylase (PyNP). Furthermore, the effect was selective for the conversion of FUra to FdUMP, as IFN alpha did not increase the cellular levels of FUTP, nor did it change the extent of incorporation of FUra into RNA (or DNA). IFN alpha also had no effect on thymidine kinase activity, the second step in the activation of FUra. Hence the effect of IFN alpha on PyNP activity is likely a critical biochemical event that modulates the cytotoxicity of FUra.

Adenosine↗