Publication: The glucose-6-phosphatase system in human development
Authors
Burchell, A. ; Hume, R.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
The classical role of glucose-6-phosphatase
in liver and kidney is the production of glucose for
release into blood. In liver, glucose-6-phosphatase
catalyses the terminal step of glycogenolysis and
gluconeogenesis. Abnormally low hepatic glucose-6-
phosphatase activity is found in human genetic
deficiencies i.e. glycogen storage disease type 1 and in
cases of developmental delay, found predominantly in
preterm infants. In contrast, abnormally high liver
glucose-6-phosphatase occurs in poorly controlled or
untreated diabetes mellitus.
Hepatic glucose-6-phosphatase is an integral
endoplasmic reticulum (and nuclear membrane) protein
and it is part of a multicomponent system. Its active site
is situated inside the lumen of the endoplasmic reticulum
and transport proteins are needed to allow its substrates
glucose-~6-phosphate (and pyrophosphate) and its
products phosphate and glucose to cross the endoplasmic
reticulum membrane. In addition, a calcium binding
protein is also associated with the glucose-6-phosphatase
enzyme. Immunohistochemical studies, in combination
with image analysis, have shown that glucose-6-
phosphatase is present in liver and kidney and also in
specific cell types in a variety of human tissues, for
example Leydig cells in the testis and some astrocytes in
the brain. Where practicable, enzymatic analysis, direct
transport assays andlor immunological detection of the
endoplasmic reticulum glucose and phosphate transport
proteins have been used to demonstrate the presence and
activity of the whole glucose-6-phosphatase system. The
distribution of the human glucose-6-phosphatase system
changes dramatically during development with a
different spatial and temporal pattern in each tissue. The
most unexpected localization was in circulating,
predominantly nucleated, embryonic and early fetal red
blood cells.
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