Purification and Properties of Adenosine Diphosphoglucose Pyrophosphorylase from Sweet Corn

A 40-fold purification of adenosine diphosphoglucose pyrophosphorylase from sweet corn (Zea mays var. Golden Beauty) revealed the enzyme to be specific for adenosine triphosphate. The enzyme has an absolute requirement for Mg(2+) and is activated by 3-phosphoglycerate and to a lesser extent by ribose-5-phosphate and fructose-6-phosphate. The apparent Km values of the enzyme for glucose-1-phosphate, adenosine triphosphate, pyrophosphate, and adenosine diphosphoglucose are 1.9 x 10(-4), 3.2 x 10(-5), 3.3 x 10(-5), and 6.2 x 10(-4)m, respectively. Pyrophosphate inhibits adenosine diphosphoglucose synthesis competitively (Ki = 3.8 x 10(-7)m), while orthophosphate and sulfate appear to inhibit the reacion noncompetitively. These results show that the production of this sugar nucleotide can be controlled by the concentration of pyrophosphate.