Reply: Request for help about M-M kinetics

From: Luann Phillips <luann@phor.com> Subject: Reply: Request for help about M-M kinetics Date: 21 Oct 1997 09:45:28 -0400 Dear NM users, I recently read a posting from Honghui Zhou (dated Sept. 17, 1997). He was trying to establish a two-compartment model with first order input and M-M output. The run was completing successfully but the PRED values were 10,000 time less than the DV. His $DES was $DES C2=A(2)/S2 DADT(1)=-K12*A(1) DADT(2)=K12*A(1)-K23*A(2)+K32*A(3)-C2*VM/(KM+C2) DADT(3)=K23*A(2)-K32*A(3) I was wondering, if the problem might be units? The term -C2*VM/(KM+C2) typically represents the change in concentration per unit time (dC/dt) and the units of Vm are [conc./time] and the units of Km are [conc.]. If Vm and Km are assumed to have the above units, then DADT(2) becomes the sum of [conc./time] and [amount/time] values which might cause problems in fitting the data. This is not a problem if Vm is intrepted to have the units [amount/time]. However if the goal is to model the M-M process using the "standard" units for Vm and Km then I think the following equation will do the trick: A(2)*VM/(KM+C2) [amount]*[conc/time]/([conc]+[conc]) Regards, Luann Phillips