A-Glucan phosphorylases

Amino acid sequence comparison of a-glucan phosphorylases. H, the potato type-H isozyme L, the potato type-L isozyme and R, rabbit muscle phosphotylase.791 The type-H isozyme sequence is used as the reference sequence only the amino acid residues that are nonidentical in the type-L isozyme and rabbit muscle enzyme are indicated. (From Biol. Chem., 266 (28), 18453 (1991)). 

Phospholylases, as summarized in Table 28.1, catalyze the reversible phospho-rolysis of polysaccharides or oligosaccharides, and produce phosphorylated mono-saccharides. Among such enzymes a-glucan phosphorylase (GP, EC 2.4.1.1), sucrose phosphorylase (SP, EC 2.4.1.7) and cellobiose phosphorylase (CBP, EC 2.4.1.20) are of great interest, since they can produce a-glucose 1-phosphate (a-GlP) from three major biomasses starch, sucrose, and cellulose. Only these three are described in this paper, a comprehensive review of other phosphorylases can be found in Kitaoka and Hayashi (2002). 

Schinzel, R., and Nidetzky, N. 1999. Bacterial a-glucan phosphorylases. FEMS Microbiol. Lett., 171,73-79. 

Takaha, T., Yanase, M., Takata, H., and Okada, S. 2001. Structure and properties of Thermus aquaticus a-glucan phosphorylase expressed in Escherichia coli. J. Appl. Glycosci., 48,71-78. 

Takata, H., Takaha, T., Okada, S., Takagi, M., and Imanaka, T. 1998. Purification and characterization of a-glucan phosphorylase from Bacillus stearothermophilus. J. Ferment. Bioeng., 85,156-161. 

Pyridoxal 5 -phosphate (PLP) was noticed to be a constituent of rabbit muscle phosphorylase in 1957, and since that time it has been shown that all a-glucan phosphorylases which give phosphorolysis products with retention of configuration contain PLP. The exact role of the PLP is still not known, though it has been shown that these a-glucan phosphorylases have an absolute requirement for PLP and that the Schiflfbase formed between PLP and glycogen phosphorylase can be reduced with borohydride without eliminating the catalytic activity of the enzyme. The P n.m.r. spectrum of PLP bound to phosphorylase b shows that deprotonation of the 5 -... 

Hustedt, H. Kroner, K. H. Stach, W. Kula, M.-R. "Procedure for the Simultaneous Large-Scale Isolation of Pullulanase and 1,4-a-Glucan Phosphorylase from Klebsiella pneumoniae Involving Liquid-Liquid Separations" Biotech, and Bioeng. 1978,20, pp 1989-2005. 

Figure 4.6 Coproduction of synthetic amylose and ethanol from cellulose via multi-enzymes and an ethanol-producing yeast. EG endoglucanase, CBH cellobiohydrolase, CBP cellohiose phosphorylase, PGP potato a-glucan phosphorylase.

Similarly, the choice of enzymes in pathway design is of importance. In the case of the conversion of cellulose to starch, cellobiose phosphorylase and a-glucan phosphorylase are responsible for reversibly eonverting from eello-biose to amylose or vice versa. It was found that a-gluean phosphorylase from potato is a key enzyme to drive the reaction toward starch synthesis. In contrast, the same enzyme from Clostridium thermocellum eannot generate amylase from cellobiose because it prefers the starch degradation direetion. ... 

Yanase M, Takaha T, Kuriki T (2006) a-Glucan phosphorylase and its use in carbohydrate engineering. J Sci Food Agric 86 1631-1635... 

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