Active glucose reactions

When a reaction is susceptible to catalysis by Bronsted acids and bases, the phenomenon is characterized as generalized acid or basic catalysis. One of the earliest reactions discovered to be subject to such generalized acid-base catalysis was the mutarotation of optically active glucose ... 

Fig. 8. Stereochemistry of reactions catalyzed by maltose phosphorylase with inversion of configuration. (A) a-Maltose synthesis from /3-D-glucopyranosyl phosphate and the reverse phosphorolysis of a-maltose (B) a-maltose synthesis from /3-D-glucopyranosyl fluoride plus a-D-glucose. X represents a protein component whose interaction with the axial 1-OH of a-D-glucopyranose is required to activate all reactions promoted by the enzyme. Reproduced from Tsumuraya et al., Arch. Biochem. Biophys., 281 (1990) 58-65, with permission of Academic Press.

UTP is a also used to activate sugars for polysaccharide synthesis, such as the reaction below, which activated glucose in glycogen biosynthesis ... 

This has the effect of "activating" glucose for incorporation into the growing glycogen chain in the next step of the process. Furthermore, this reaction is made essentially irreversible by hydrolysis of the pyrophosphate to 2Pi. 

Figure 5. Effect of heating on enzyme activity (6). Reaction mixtures contained substrate (2 mg.), 0.1M—acetate-buffer, pH—5.0 (2.0 ml.), and 0.1 ml. of an enzyme solution that had previously been held at the temperature shown for 10 min. Glucose equivalent was then estimated by the standard assay procedure described in the text...

ACTIVE FIGURE 22.15 The Calvin cycle of reactions. The number associated with the arrow at each step indicates the number of molecules reacting in a turn of the cycle that produces one molecule of glucose. Reactions are numbered as in Table 22.1. Sign in at www.thomsonedu.com/login to explore an interactive versien ef this figure. 

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