d-Glucose 6-Phosphate Cycloaldolase: Inhibition Studies and Aldolase Function

d-Glucose 6-phosphate cycloaldolase is inhibited 83% by 0.66 mm EDTA and stimulated 1.7-fold by 0.6 mm KCl. Dihydroxyacetone phosphate, an analog of the last three carbons in the proposed intermediate, d-xylo-5-hexulose 6-phosphate, acts as a partially competitive inhibitor. Treatment with NaBH₄ in the presence of dihydroxyacetone phosphate does not cause permanent inactivation as would be expected if a Schiff base were being formed. In these properties it resembles a type II, metal-containing aldolase. Photooxidation in the presence of Rose Bengal inactivates this enzyme. NAD⁺ partially protects against this photooxidation. Cells grown on medium lacking myoinositol had four times as much enzyme activity as cells grown on medium containing 100 mg of myoinositol per liter.