Activation of rat-liver microsomal glucose 6-phosphatase, inorganic pyrophosphatase and inorganic pyrophosphate-glucose phosphotransferase by hydroxyl ion

Abstract

• 1.

  1. OH- has been shown to produce a 2- to 3-fold increase in the apparent activity in vitro of rat-liver microsomal glucose 6-phosphatase (EC 3.1.3.9) and the related enzymatic activities, inorganic pyrophosphatase, inorganic pyrophosphate-glucose phosphotransferase and adenosine-5′-triphosphate-glucose phosphotransferase.

• 2.

  2. Optimal activation is achieved by pre-treatment of liver microsomes with ammonium or amino acid buffers at pH 9.5–9.8. Inactivation is observed above pH 10.

• 3.

  3. This activation is as great or greater than that produced by deoxycholate or Triton X-100 treatment and the thermal instability introduced by these reagents is avoided.

• 4.

  4. Alteration of the microsomal membranes by treatment with base is accompanied by a decrease in turbidity but does not result in a solubilization of the enzyme. The essential protein-lipid binding is apparently retained and the enzyme, so treated, is relatively stable at 30°.

• 5.

  5. NH₄OH pretreatment of microsomes results in a lowering of the apparent Michaelis constant for glucose 6-phosphatase, similar to that caused by digitonin, deoxycholate and Triton X-100.