Phosphorolytic synthesis

Phosphorolytic Synthesis of Low-Molecular-Weight Amyloses with Modified Terminal... 

Molecular weight distribution (SEC/LALLS) of LMWA with modified terminal groups obtained by phosphorolytic synthesis either by potato phosphorylase (II) (72) and (III) (58) or muscle phosphorylase b (62). 

Table III. Development of chain length distribution of LMWA with modified terminal groups during phosphorolytic synthesis. Enzyme potato phosphorlyase. Concentration in mol % calculated from HPLC. DP Maxima written in italic...

Figure 3. Chain length distribution of LMWA during phosphorolytic synthesis after a, 5 and b, 40 min by potato phosphoiylase. Continued on next page.

Formation and Cleavage of Macromolecules. Cleavage is mostly hydrolytic (occasionally phosphorolytic). Synthesis, however, employs group transfer. 

Purine nucleoside phosphorylase (PNP, E.C. 2.4.2.1) catalyzes the reversible phosphorylysis of ribonucleosides and 2 -deoxyribonucleosides of guanine, hypoxanthine, and related nucleoside analogs [1]. It normally acts in the phosphorolytic direction in intact cells, although the isolated enzyme catalyzes the nucleoside synthesis under equilibrium conditions. Figure 1 shows the chemical reaction. 

Histochemical studies on the enzymes of Hymenolepis diminuta (Rud., 1819) (Cestoda). V. Some enzymes of the synthesis and phosphorolytic degradation of glycogen in mature cestodes. Acta Parasitologica Polonica, 23 569-92. 

Another major difference between the phosphorylase-catalyzed reaction and the reaction of hydrolases is the free reversibility of the phosphorolytic cleavage. However, under certain conditions, the reaction of the hydrolysis is reversible, and may result in the synthesis of higher oligosaccharides from maltose and related di- and trioligosaccharides (as studied by French and Hehre in the 1960s and 1970s). 

Phosphorolytic attack of thioester by inorganic compounds provides a mechanism for introducing high energetic phosphate esters into metabolism leading to the synthesis of pyrophosphate as the first unit of energy. The synthesis of AMP and ATF followed this step. 

The glycosyl transfer activity seems to be more sensitive with regard to the pH dependence. The pH-optimum for both enzymes is reported in the range between pH 4.9 and 8.7 (17,22,26). Particular specifications of optimum pH values for synthesis and for degradation differ. In general, phosphorolytic degradation should not occur at pH 5.5 or 6.0. But it has to be considered that the disproportionation reaction is due to a synthesis/degradation equilibrium especially at pH 7.0. 

The free energy change in phosphorolysis compared to hydrolysis is much closer to zero, and thus the known phosphorolytic enzymes catalyze biosynthetic reactions as well as catabolic changes. They are implicated chiefly in the synthesis of starch by plants and glycogen by animals. Recent work by Kornberg and his associates has pointed to a pyro-phosphorylase in yeast and hog liver that catalyzes the following general reaction ... 

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