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Someone asked if glucose and insulin could be mixed in the same container and used as an injection to provide a quick energy boost. I'm not interested about the medical part of this question, but just if glucose and insulin (which is a protein) could exist in the same container without reacting with each other without forming some sort of glycoprotein. Is it possible to make a reasonable prediction what would/not happen in the mixed glucose/insulin solution in the container?

I know that insulin and glucose do not react with in the body, I want to know if in aqueous solution they would react.

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Glycoproteins come in O-linked and N-linked forms. For O-linked sugars, a glycosidic bond forms between the sugar and the hydroxyl of a serine or threonine side chain. For N-linked sugars, a glycosidic bond forms between the sugar and the amide of asparagine. The equilibrium for all these reactions lies on the side of hydrolysis in aqueous solution.

Is it possible to make a reasonable prediction what would/not happen in the mixed glucose/insulin solution in the container?

Yes, in aqueous solution there is no expectation that a glycoprotein forms between insulin and glucose. In vivo, glycoproteins form in a coupled reaction involving the carbohydrate (usually an oligosaccharide rather than a single glucose), the protein and a nucleotide triphosphate.

However, if an individual has high blood sugar levels (i.e. high concentrations of glucose in the blood) for extended periods of time, hemoglobin (specifically, the N-terminal amino group and the sidechain amino group of lysine) will react with the sugar and become glycalated. This is used in the HbA1c diagnostic test for checking if someone has diabetes. After the sugar binds (reversibly), there is a further reaction (Amadori rearrangement) that leads to a long-lasting product.

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    $\begingroup$ OK. Is there any enzyme required for the formation of glycoproteins in vitro ? $\endgroup$ – Jan Apr 15 at 17:56
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    $\begingroup$ It would not form because the equilibrium lies on the side of the reactants. $\endgroup$ – Karsten Theis Apr 15 at 17:57

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