Question

why are certain regions of an enzyme are more likely to mutate?

Answer 1

In general, each nucleotide has equal probability to undergo mutation. But, the frequency of a mutation in a population depends upon the effect exerted by the mutation.

For example, if a mutation occurs in a non-essential region of a protein, it does not affect the protein function. So, it can be maintained in the population. But, if a mutation occurs in an essential region (catalytic site) of protein, the protein loses its function. So, it can not be maintained in the population.

It also depends upon the type of mutation. Since the genetic code is redundant, many of mutations are synonymous or do not cause any change. Such mutations do not alter the protein function even if they occur in the essential region. So basically, the sequence context and the type of mutation determines the effect of the mutation on a protein function.