There are often multiple names for enzymes and the conscientious searcher will want to track them all down. I’m not sure that any one resource offers a one stop shop solution but the ExPASy Enzyme database is a pretty good place to start – providing alternative names and EC numbers. The MeSH indexing system is also pretty well updated in this area. Whether or not you are searching Medline/Pubmed you can check for alternative names and hierachies using the MeSH Browser