Biochemistry - The Chemical Reactions of Living Cells Volume 2 - D. Metzler 1980

Enzymes: Cellular Protein Catalysts
Regulation of Enzymatic Activity
Cross-Regulation

A metabolite can regulate not only its own Biosynthesis via negative feedback, but also the synthesis of another compound produced via an entirely different pathway [66]. A striking example of this is the synthesis of ATP and GTP from a common precursor, inosine monophosphate (IMP; Fig. 6-17). Both ATP and GTP are required by Cells primarily for RNA and DNA Synthesis, so it is not surprising that their production is balanced by specialized regulatory mechanisms. As shown in Figure 6-17, the synthesis of AMP from IMP requires the direct participation of GTP, whereas the synthesis of GMP involves ATP. The biosynthesis of both AMP and GMP is inhibited by negative feedback. In addition, special mechanisms exist for the Hydrolysis of excess amounts of ATP and GTP (outer loops in Fig. 6-17). However, the hydrolysis of AMP is inhibited by GTP, and the reductive deamination of GMP is inhibited by ATP.



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