Abstract
1. A phosphokinase catalyzing the phosphorylation of sedoheptulose with ATP was found in a cell-free extract of a Bacillus species, Strain W-2, grown in the presence of this sugar.
2. An equimolar relationship was observed between the disap-pearance of free heptose and the decrease of acid-labile phosphate in the phosphokinase reaction. This suggests that the reaction product is a sedoheptulose monophosphate.
3. The reaction products were isolated as crude barium salts which gave a spot corresponding to sedoheptulose on paper chromatogram after (but not before) hydrolysis by a phosphatase preparation.
4. The pH-activity curve of this enzyme has two maxima at pH 6.4 and 9.0.
5. The enzyme requires Mg++or Mn++for its activity, Mn++being less effective as activator.
6. NaF, NaN3, iodoacetate, Cu++, and alloxane are inhibitory to the enzyme. The inhibition by alloxane can be reversed by cysteine.
7. Several common hexoses and pentoses are inactive to the enzyme. They do not interfere with the phosphorylation of sedoheptulose.
The authors are indebted to Prof. T. Ishikawa and Dr. Y. Kurata of the Department of Pathology, Faculty of Medicine, Kanazawa University for their kindness in making their instruments available to the authors.
