Pathology of Glucose-6-phosphatase

Cori and Cori have drawn attention to the fact that abnormal storage of glycogen in skeletal muscle or heart muscle cannot be explained by a lack of G-6-Pase since this enzyme is normally absent from these tissues. Their suggestion that the activity of amylo-l,6-glucosidase be measured in these tissues has been followed up, and a deficiency of this enzymatic activity in muscle glycogen storage disease has been established (Illingworth et al., 1956). 

Attempts to Influence Hepatic Glucose-6-phosphatase in Glycogen Storage Disease 

These studies of neoplastic tissues were done on homogenates prepared in isotonic sucrose. Investigation was also carried out to determine whether G-6-Pase activity could be demonstrated under different assay conditions. Since most of the normal liver G-6-Pase activity is concentrated in the microsomal fraction, the possibility arose that in a homogenate prepared in isotonic sucrose the hepatoma microsomes were not broken and G-6-Pa.se could not be liberated or the substrate could not reach the enzyme. 

However, NovikofT hepatoma homogenates prepared in isotonic NaCl or in distilled water also had no G-6-Pase activity. Preparation of more concentrated (20 %) or highly diluted (1 %) hepatoma homogenate also failed to show any G-6-Pase activity (Weber and Cantero, 1955a, b). 

It was also shown that the absence of G-6-Pase activity in neoplastic tissues is not due to the presence of an inhibitor, since homogenates of adenocarcinoma or hepatoma did not inhibit reaction mixtures containing normal liver. A 1-hour preincubation of various tumor homogenates with normal liver homogenate, prior to the enzyme assay, was also without any effect on the G-6-Pase activity of the normal liver (Weber and Cantero, 1955a). 

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