Glucosyl arsenate

In the direction of degradation, phosphate can be replaced by arsenate, although the reaction is much slower. The product is free D-glucose, and it was assumed that D-glucosyl arsenate is formed, and then spontaneously hydrolyzed. 

The mechanism of arsenolysis is thought to be very similar to that of phosphorolysis. It is believed that D-glucosyl arsenate is formed. 

Arsenate can act as an acceptor with P-enzyme, but D-glucose is the product. It is believed that a-D-glucosyl arsenate is formed initially, and that this is imstable and decomposes. The extent of arsenolysis of amylopectin is about the same as that of jS-amyloIysis (55-70%), although, in other experiments, the latter was about 15% more than the degree of... 

One property of phosphorylase that has not been widely used, but that could often be advantageous, is its ability to degrade or-n-glucans, releasing D-glucose instead of D-glucosyl phosphate when the reaction is conducted in the presence of arsenate rather than phosphate. It is considered that D-glucosyl arsenate is formed initially, but that it is labile... 

Many phosphorylases are activated by adenosine 5 -phosphate, and Michaelis constants for the binding of adenosine 5 -phosphate to the enzyme have been found. The Km for adenosine 5 -phosphate depends on the concentrations of D-glucosyl phosphate and inorganic phosphate, and decreases as their concentrations increase. Addition of adenosine 5 -phosphate has a similar effect on the Km for glycogen, D-glucosyl phosphate, inorganic phosphate, and arsenate that is, the Km values decrease as the concentration of adenosine 5 -phosphate increases. " Values of Km for adenosine 5 -phosphate of 0.2 to 1.5 fiM, 50 fiM, 60—100 fiM, 47 juM, and 25 p,M have been found with the phosphorylases from rabbit-muscle a-form, - rabbit-muscle b-form, rabbit liver, lobster-muscle b-form, and turtle heart, respectively. 

A double-displacement mechanism is unlikely, for D-glucose is not found in a system containing potato phosphorylase, arsenate, and D-glucosyl phosphate. ... 

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