AN ANION-STIMULATED ADENOSINE TRIPHOSPHATASE FROM POTASSIUM-TRANSPORTING MIDGUT OF LARVA OF LARVA OF HYALOPHORA CECROPIA

1. 1. Some properties of an adenosine triphosphatase (EC 3.6.1.4.) present in 40 000 × g sediment of the midgut epithelium of the larva of Hyalophora cecropia are described. 2. 2. The ATPase has an optimum activity at pH 8.7 and is sensitive to anions. In the presence of magnesium, bicarbonate and to an even greater degree borate and selenite enhance the activity compared to halogens ions, while thiocyanate acts as an inhibitor. When magnesium is replaced by calcium no stimulation by bicarbonate is found. 3. 3. Alkali metal ions have only slight influence on the activity. With bicarbonate or borate as anion, potassium and rubidium are slightly more stimulating than sodium and lithium. 4. 4. The alkaline-phosphatase activity (EC 3.1.3.1) of the preparation with p-nitrophenylphosphate as substrate, has a pH optimum of 10.0 and an anion sensitivity which is less pronounced and different to that of the ATPase. 5. 5. Imidazole gives a lower ATPase activity than buffer compounds with a primary amino group. © 1968.