A New Complex of the Glucose Phosphate Isomerase Ribozyme with the Enzyme Hexokinase in Yeast

Abstract

The existence of a previously unknown ribozyme with the catalytic function of glucose phosphate isomerase was shown. It catalyzes the interconversion of glucose 6-phosphate and fructose 6-phosphate. This ribozyme was found in baker’s yeast Saccharomyces cerevisiae and was isolated as a complex with the enzyme hexokinase. The complex was easily isolated on an immunoaffinity column with antibodies to hexokinase. The ribozyme consists of 41–42 nucleotides and has a molecular weight of about 14.15–14.5 kDa. Km and Vmax are accordingly 0.14 ± 0.02 mM and 14.0 ± 1.3 U/mg for glucose 6-phosphate and 0.2 ± 0.03 mM and 15.4 ± 1.4 U/mg for fructose 6-phosphate. These kinetic characteristics are approximately the same in the complex and for the free ribozyme. Hexokinase within the complex retains its catalytic activity.