The mechanism by which an enzyme interconverts a derivative of glucose with a derivative of galactose is very interesting in its own right, but perhaps we should put that off for a bit. For now suffice it to say that an enzyme is necessary.
Ah, that’s great - thank you. Rather naively, I hadn’t realised that a mechanism was involved. I assumed that it was just a physical rotation rotation.
With reference to and without a pictorial mechanism of galactose and glucose, why can’t/ doesn’t mutarotation occur on C1 of glucose thus converting to galactose
With respect to the interconversions of the alpha and beta forms of glucose, two of the three mechanisms I have seen show a transient opening of the ring. That is not possible at the C-4 position of glucose.
The compound uridine diphosphoglucose can be turned into uridine diphosphogalactose by briefly oxidizing C-4 (a hydride ion is removed). Then the hydride ion is put back onto the opposite face of the molecule. Bonds have to be made and broken to interconvert the two compounds. The enzyme that does is is called UDP-galactose 4-epimerase.