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Old 03-19-2012
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Biochemistry Glucose 6 phosphatase deficiency

Kaplan Lecture Notes Biochemistry book says - in a person with this glucose 6 phosphatase deficiency, ingestion of Galactose or Fructose causes no increase in blood glucose..
can anybody explain why?
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Old 03-19-2012
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I guess you are confused between Fructose and sucrose , Galctose and lactose ! Ga-lactose and Fructose are monsuccarides ..
Fructose enter cells, phosphorylated andcleaved to DHAP and glyceraldehyde may contribute in Gluconeogenesis if needed ..
Galactose also enter cells phosphorelated and switched to Glucose P..

notice that when they r turning to Glucose this gulcose has P on it. iT cannot be released out of cells without Glucose 6 phosphatase removing this P.. that's why Glucose accumulate in cells as Glucose 6P, not in blood

Hope that helped !!
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Old 03-19-2012
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Originally Posted by vna.rao22 View Post
Kaplan Biochem says- in a person with this deficiency, ingestion of galactose or fructose causes no increase in blood glucose.. can anybody explain why?
in the pathways of galactose and fructose metabolism, they are converted to galactose 1-P or fructose 1-P, which is then converted to glucose 1-P by the UDP-transerase thingy (in galactose metabolism) and then glucose 6-phosphate, or to DHAP by aldolase B (in fructose metabolism) and then enters gluconeogenesis to yield glucose 6-phosphate.

we then know glucose 6-phosphatase is responsible for converting glucose 6-phosphate into glucose (the opposite effect of hexokinase or glucokinase, in glycolysis), but we have a deficiency so this step cannot be completed suffieciently.

basically, these 2 sugars rely on gluconeogenesis to be converted to glucose, and the last step in gluconeogenesis is glucose 6-phosphatase, and since we have a deficiency of this enzyme, this last step cannot be completed.
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