![Figure 4. Comparison of PI and P2Y1 modules to experimental data. (A) At t = 0, platelets were treated with 27 nM of thrombin, and the levels of PtdIns, PIP, and PIP2 were measured (data obtained from Wilson et al32). To simulate this turnover in the PI module, [PLC-β*] was raised to 1 μM and PI levels were calculated over time. Average results from 100 simulations are plotted as solid lines. (B,C) Kinetic parameters in the P2Y1 module were fit to GTP hydrolysis measurements from proteoliposome assay containing 300 nM of P2Y1, 1 μM of Gα·GDP, 3 μM of Gβγ, 2 μM of GTP, RGS4, and 2MeSADP (data obtained from Waldo and Harden21). Best-fit simulation results are plotted as solid lines. (B) Time-course GTPase activity is shown with (■) or without (□) 100 nM of RGS4. (C) P2Y1 dose-response to 2MeSADP in the absence (□) or presence (■) of 100 nM of RGS4. In the final platelet model, Kd and kcat values for ADP-binding and PLC-β-mediated hydrolysis, respectively, were substituted for the 2MeSADP- and RGS4-mediated activities used in the calibration procedure shown here.](https://ash.silverchair-cdn.com/ash/content_public/journal/blood/112/10/10.1182_blood-2008-05-157883/7/zh80180824300004.jpeg?Expires=1735590031&Signature=muodokDzExNr5FZVWrG~y-~0Oml-MPKrc~ElWWhp3XDw01H5Jo~EN4FZf7n6xlQOie4AXhgBMPxoT8u77S1K-WmTSIuwis4IMPFClk7SR4etDPjjfP-jmkJg7bbKnBX5Q3asMr~WUyC0lh0UhhvmMK70ouR6t0NZ6v9OVqOIydnr7A~Ps9NWfi9lUFaIpJERNN5B6TKTr8zSxuAOhzIyzSB3o6t9YFhuIaBd0ZysW8m4roFV7hvLT5xKMFBNu72xxmZ6V~CQE8u8Hp-ZZl70p4Z--XhdzzJWDNzknd8zs9EvzdmUWTW5BCxxU-Ynoir5sOsWXf50I6qpbbP0eMHunw__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
Comparison of PI and P2Y1 modules to experimental data. (A) At t = 0, platelets were treated with 27 nM of thrombin, and the levels of PtdIns, PIP, and PIP2 were measured (data obtained from Wilson et al32 ). To simulate this turnover in the PI module, [PLC-β*] was raised to 1 μM and PI levels were calculated over time. Average results from 100 simulations are plotted as solid lines. (B,C) Kinetic parameters in the P2Y1 module were fit to GTP hydrolysis measurements from proteoliposome assay containing 300 nM of P2Y1, 1 μM of Gα·GDP, 3 μM of Gβγ, 2 μM of GTP, RGS4, and 2MeSADP (data obtained from Waldo and Harden21 ). Best-fit simulation results are plotted as solid lines. (B) Time-course GTPase activity is shown with (■) or without (□) 100 nM of RGS4. (C) P2Y1 dose-response to 2MeSADP in the absence (□) or presence (■) of 100 nM of RGS4. In the final platelet model, Kd and kcat values for ADP-binding and PLC-β-mediated hydrolysis, respectively, were substituted for the 2MeSADP- and RGS4-mediated activities used in the calibration procedure shown here.
