Pyridoxal phosphorolysis

Fig. 5 Catalytic mechanism of glycogen phosphorylases. The reaction scheme accounts for the reversibility of phosphorolysis of oligosaccharides (R) in the presence of orthophosphate (upper half) and primer-dependent synthesis in the presence of glucose-l-phosphate (lower half). PL enzyme-bound pyridoxal BH-f a general base contributed by the enzyme protein. Reprinted with permission from [109]. Copyright 1990 American Chemical Society...

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 -... 

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