ACTIVATION IN VITRO OF GLUCOSE-6-PHOSPHATASE, INORGANIC PYROPHOSPHATE-GLUCOSE PHOSPHOTRANSFERASE AND RELATED ENZYMES - RELATIONSHIP TO MICROSOMAL MEMBRANE STRUCTURE

1. 1. The elevation in enzymatic activity of certain microsomal enzymes caused in vitro by treatment with NH4OH or deoxycholate has been studied in relationship to the appearance of the membranes in corresponding electron micrographs. 2. 2. When freshly prepared liver microscomes were treated at 0° with NH4OH (about pH 9.8), activation of glucose-6-phosphatase (EC 3.1.3.9), inorganic pyrophosphatase, inorganic pyrophosphate-glucose phosphotransferase and inorganic pyrophosphate glycerol phosphotransferase was not instantaneous. 3. 3. Exposure to NH4OH for 15 to 30 min at 30° or contact for many hours at o° resulted in a maximum in vitro elevation of the enzyme activities that was approximately quantitatively equal to that observed instantaneously with such detergents as deoxycholate or Triton X-100. 4. 4. An electron microscopic study of NH4OH-activated microsomes at 0° showed that ribosomes were largely retained on the membranes when about 50% of maximum stimulation of enzymatic activities occurred. Longer exposure at 0° or brief warming at 30° with NH4OH, effecting full enzymatic activation, resulted in detachment of most of the ribosomes. The resulting membranes resembled those seen after exposure to inorganic pyrophosphate. 5. 5. The enzymatic activity of smooth microsomal membrane subfractions was capable of a percentage increase in vitro as great or greater than that of ribosome-rich rough membranes. 6. 6. Activation in vitro of these membrane enzymes is probably due to conformational changes in the membrane itself rather than to removal of ribosomes from their membrane attachment. © 1969.