Glucose becomes a better leaving group.
In a manner similar to how protonation of an alcohol makes it easier to substitute a -OH group, glucose becomes a better leaving group when the oxygen atom is protonated.
A substance that releases or donates hydrogen ions during a chemical reaction is referred to as a Bronsted-Lowry acid. A Bronsted-Lowry base, on the other hand, takes hydrogen ions. Another way to look at it is that a base accepts protons whereas a Bronsted-Lowry acid donates them. Amphoteric species are those that, depending on the circumstance, can either give or take protons.
Every Bronsted-Lowry acid gives a species that is its conjugate base a proton in exchange for the species' support. Each base in the Bronsted-Lowry system similarly accepts a proton from its conjugate acid.
I understand the question you are looking for is this:
For what mechanistic reason does G1 of lactase first act as a Bronsted acid during catalysis?
A) G1 becomes a better nucleophile
B) G2 becomes a better nucleophile
C) Glucose becomes a better leaving group.
D) Galactose becomes a better leaving group.
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