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While going through gluconeogenesis I came to know about Glucose-6-phosphatase. In my book it's stated that

Glucose-6-phosphatase is mostly present in liver and kidney and is absent in muscles, brain and adipose tissue.

I want to be specific that whether it is true for all muscles or only 1 type of muscle.

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  • Welcome to this community! Have you considered asking this on the Biology Stack Exchange? Feb 28, 2022 at 20:09
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    Welcome. For others to learn what you are learning, could you please provide details of your textbook? Mar 1, 2022 at 5:23

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In humans, glucose-6-phosphatase is actually a multiunit enzyme system (Hutton and O'Brien 2009. PMCID 2785553). There are at least 3 isoforms.

G6PC

The first isoform, encoded by the G6PC gene, is predominantly expressed in liver and kidney as is indicated in your textbook (Hutton and O'Brien 2009. PMCID 2785553).

The most well studied function of glucose-6-phosphatase is in gluconeogenic tissues where it catalyzes the removal of phosphate to prepare the glucose molecule for transport outside of the cell.

enter image description here Adapted from this image and this image.

Although most gluconeogenesis occurs in the liver, some occurs in the kidneys (Clar et al 2014 PMCID 5678048).

Patients with biallelic pathogenic variants of G6PC have glycogen storage disease 1a which is characterized by severe hypoglycemia and hepatomegaly caused by the accumulation of glycogen.

G6PC3

The third isoform, encoded by the G6PC3 gene, is the more broadly expressed. Some authors call it "the ubiquitously expressed glucose-6-phosphatase" (Martin et al 2002. PMID 12370122). The function of this isoform is more poorly understood. Hutton and O'Brien note that some authors have theorized that

the presence of G6PC3 in muscle may explain the improvement in endogenous glucose production and the decrease in susceptibility to hypoglycemia in patients with GSD type 1a after puberty.

The Human Protein Atlas shows that G6PC3 is expressed in cardiac, skeletal and smooth muscle.

enter image description here

I have been unable to find any expression datasets which compare fast and slow twitch skeletal muscle.

Patients with biallelic pathogenic variants of G6PC3 have Dursun syndrome which is characterized by neutropenia and cardiac abnormalities which demonstrates the effect outside of the liver and kidney.

Conclusions

Thus, your textbook is correct that the G6PC gene is largely expressed in the liver and kidney where is is involved in gluconeogenesis. However, other isoforms of glucose-6-phosphatase are expressed outside the kidney and liver, including in muscles.

The function of the second isoform, encoded by the G6PC2 gene is more controversial, so I will leave it to the reader to explore more (Hutton and O'Brien 2009. PMCID 2785553).

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    When referencing sources through superscript numbers, it may look neat in some respects, but the linking provided can be small and difficult to use on a mobile phone screen. Could you please provide a list of your numbers and references at the bottom of your answer? Not only then does this make navigation easier, it provides the information when printed (if anyone wished to do so). Mar 1, 2022 at 5:28
  • Also, I feel that while simple definition linking is fine with just a direct link, if a link is provided to a journal article for example like your link to "Some authors have theorized that", source information, I think, should be readily recognised and again viewable in printed form. [Just some friendly suggestions] Mar 1, 2022 at 5:37
  • I think we are all biased towards our own fields when it comes to reference styles. You may prefer APA because you work in that field. I am primed to prefer this style because it minimizes the number of characters used so you can cram more information into that 12 page grant. To me, the reference list at the bottom is a bit messy. I can certainly see your points though. If meta consensus is reached (I upvoted that one weeks ago), I am more than willing to change my behavior.
    – Ian Campbell
    Mar 1, 2022 at 5:43

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