I understand the evolutionary side of the reasoning, but not so much the biochemical side. 

How can an enzyme such as, alcohol dehydrogenase, be able to metabolize so many different

substrates? Is it that the catalytic site is "ambiguous" or freely moving to accept a wide range of substrates?

Or is it that the enzyme has multiple sites for substrates? 

 

~ee

Most commonly it is due to promiscuity on their active site. It is assumed that early enzymes had little substrate specificity and were accordingly less effective. Specialization increased both, specificity as well as catalytic activity. In addition, there are compounds (or even just parts ) who are structurally similar and would not be distinguishable for the enzyme (depending on the specificity of the active site).

Alkaline phosphatase is relatively unconcerned with the R group in the phosphomonoester that it hydrolyzes to an alcohol (ROH) and inorganic phosphate.  It is my understanding that the R group does not interact strongly with the active site but points away from it.  I don't have a citation handy.  I am not sure about alcohol dehydrogenase, but it might be a good working hypothesis.