Glucose-6-phosphatase in normal adult human intestinal mucosa

1. The existence of specific glucose-6-phosphatase activity in human intestinal mucosa has been somewhat controversial. 2. We have demonstrated the presence of low levels of specific glucose-6-phosphatase activity in normal human adult intestinal mucosa. Activity was found in oesophagus, stomach, duodenum and colon. 3. Immunoblot analysis using antibodies monospecific for the 36.5 kDa liver glucose-6-phosphatase catalytic subunit demonstrated that intestinal mucosa contains low levels of the glucose-6-phosphatase enzyme protein. 4. The low levels of activity together with problems of proteolysis make human intestinal biopsies unsuitable for use in the diagnosis of type 1 glycogen-storage disease.

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ENZYME INDUCTION IN A CASE OF GLYCOGEN STORAGE DISEASE

PEDIATRICS ◽

10.1542/peds.38.1.111 ◽

1966 ◽

Vol 38 (1) ◽

pp. 111-121 ◽

Cited By ~ 2

Author(s):

Shimon W. Moses ◽

Stanley Levin ◽

Reuben Chayoth ◽

Kurt Steinitz

Keyword(s):

Phosphatase Activity ◽

Structural Gene ◽

Enzyme Induction ◽

Storage Disease ◽

Regulatory Gene ◽

Glycogen Storage ◽

Enzyme Synthesis ◽

Gene Defect ◽

Low Levels ◽

Enzyme Biosynthesis

In cases of glycogen storage disease Type III, low levels of liver glucose-6-phosphatase activity have frequently been found in addition to the complete absence of amylo-l, 6-glucosidase activity. Glucose-6-phosphatase regulates a key reaction in the homeostatic control of gluconeogenesis. It belongs to the group of adaptive enzymes, and it has been shown in rats that its activity can be induced by steroids and suppressed by insulin. Increasing evidence is accumulating to indicate that the hormonal control of this enzyme activity affects de novo synthesis at the gene level. The subnormal activity of glucose-6-phosphatase in cases of amylo-1, 6-glucosidase deficiency could be the result of a double enzyme deficiency due to two structural gene defects, or secondary to a regulatory gene disorder resulting in suppression of glucose-6-phosphatase biosynthesis. If the low levels of glucose-6-phosphatase activity result from a structural gene mutation, hormonal induction of enzyme biosynthesis would be unlikely; whereas, if the markedly depressed activity of this enzyme is due to abnormal control affecting the regulation of enzyme synthesis, hormonal induction may be possible. A case of amylo-1, 6-glucosidase type A is presented in which, in addition to complete absence of the debrancher enzyme, exceedingly low values of liver glucose-6-phosphatase were repeatedly demonstrated. Low insulin-like activity was found in the patient's plasma, but no significant abnormality of steroid metabolism could be shown. Triamcinolone administration resulted in fourfold increase of liver glucose-6-phosphatase activity. This enzyme induction by Triamcinolone suggests that the markedly reduced levels of glucose-6-phosphatase activity prior to steroid administration were due to a regulatory disorder of enzyme biosynthesis and not to a structural gene defect. It is suggested that the Triamcinolone induction test can be used in similar situations as a diagnostic tool to differentiate between a regulatory gene disorder affecting enzyme synthesis, and a structural gene defect.

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