Each frame on this page can be independently resized. This page uses JavaScript to simulate the pulse-chase labeling kinetics of intermediates B, C and D in the simple metabolic pathway shown above (top left frame). The pathway receives stable isotope label from a precursor, A, supplied at a high isotope abundance at zero time. The isotope abundance of A can be reduced at a user-designated time to simulate a "chase". The image shown above illustrates the Visual Basic version of this same model, and its graphical ouput, using the same default values of pool sizes, fluxes, isotope abundance and times as specified in the lower right frame. Definitions of the variables are given in the upper right frame.

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 (lower right frame) 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!

Starting values should be in numerical format, and should not exceed 6 characters in length. Errors resulting in script termination will occur when values are entered as text rather than in numerical format. Upon encountering such errors it may be necessary to "Refresh" the page.

To disable the "chase" function, enter a TC value which is greater than TS. After entering starting values (inputs), click the Calculate button. Simulated values will then be displayed in the text boxes below the "Calculate" button. The Calculate button can be reused repetitively after modifying input values.

With certain browsers (e.g. Internet Explorer 3.0), the computed values of isotope abundance and pool sizes displayed in the text boxes (lower right frame) 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 suspected to be less than 0.1.