Enzymatic reactions that happen when water and wheat flour is mixed?

Yes, flour contains enzymes, and they get activated when you mix the flour and water.

The enzymes in flour are diastase, amylase, and protease. The diastase breaks down starch into maltose, amylase produces other types of sugars from starch, and the protease breaks down the proteins in the flour.

Commercial flours are typically balanced for optimal fermentation with yeast, because these reactions are less important in other types of baking. But note that yeast brings in its own enzymes, which complicate the picture, and then, for some breads, enzymes are added from outside to get specific effects, such as using malted barley for dark breads.

This has nothing to do with sprouting, the parts of the seed which would sprout are removed when making flour. Unless you have real whole grain flour, but there the embryo is also already killed, and the producer has made sure that the enzymes are at the right level.

Yes! There is an enzymatic reaction called 'autolyse'. In many no-knead bread recipes it is a separate initial step in the recipe done with just flour and water before any salt or yeast are added.

Here is an article describing the technique and some of the magical results: https://www.kingarthurbaking.com/blog/2017/09/29/using-the-autolyse-method

In addition to hydrating the flour...

• The protease enzymes degrade the protein in the flour, which encourages extensibility.
• The amylase enzymes turn the flour's starch into sugars that the yeast can consume.