This page uses JavaScript to simulate the radiolabeling kinetics of intermediates **A**, **B**, **C** and **D** in the metabolic scheme shown above, with radiolabel derived from an exogenously supplied precursor, **E**. **The JavaScript language is supported by both Netscape Navigator and Microsoft Internet Explorer 3.0 or above**. If you are using a JavaScript-compatible browser, try varying the pool sizes and fluxes to determine how this influences the labeling patterns. Note than when the rate of synthesis exceeds the rate of utilization, the pool will expand with time. When the rate of utilization exceeds the rate of synthesis, the pool will deplete with time. *If a pool becomes zero during the time-course, the simulation will terminate before completion!*. A key variable for adjustment is the value of **k**, which determines the rate of uptake of the exogenously supplied precursor, **E**. As **k** is increased, so is the rate of uptake of **E**. The pool of **A** will expand at the uptake rate of **E** assumed.

** Starting values [values should not exceed 5 characters in length]:**

Enter E1: ^{-1}))

Enter E2: ^{-1}))

Enter A1: ^{-1}))

Enter A2: ^{-1}))

Enter A3: ^{-1}.gfw^{-1}))

Enter A4: ^{-1}.gfw^{-1}))

Enter F1: ^{-1}))

Enter B1: ^{-1}))

Enter B2: ^{-1}))

Enter B3: ^{-1}.gfw^{-1}))

Enter B4: ^{-1}.gfw^{-1}))

Enter C1: ^{-1}))

Enter C2: ^{-1}))

Enter C3: ^{-1}.gfw^{-1}))

Enter C4: ^{-1}.gfw^{-1}))

Enter D1: ^{-1}))

Enter D2: ^{-1}))

Enter D3: ^{-1}.gfw^{-1}))

Enter time scale of the labeling simulation:

Enter k: ^{-1})

After entering starting values, click the **Calculate** button. Simulated values of radioactivity in each pool and pool size will then be displayed in the text boxes below (the radioactivity in a given pool is equal to the pool size (nmol.gfw^{-1}) multiplied by the specific activity (nCi.nmol^{-1}) of the pool; e.g. radioactivity in pool **A** = A1 * A2 (nCi.gfw^{-1})). The **Calculate** button can be reused repetitively after modifying input values.

** Computed time-courses of radioactivity in each pool (nCi.gfw ^{-1}) and pool size (nmol.gfw^{-1}):**

With certain browsers (e.g. Internet Explorer 3.0), the values displayed in the text boxes above are double-precision floating-point (e.g. 0.019995 may be displayed as 1.9995E-02). Thus, it may be necessary to use your mouse to highlight certain text boxes to view the full double-precision floating-point notations for values of less than 0.1 (e.g. simulated values of E1*E2 at times greater than 250 min using the default starting values above). Errors resulting in script termination will occur when inputs are entered as text rather than as numerical values. Upon encountering such errors it may be necessary to "Refresh" the page.