i·som·er·ase (?-s?m??-r?s?)n. Any of a class of enzymes that catalyze the conversion of one isomer into another.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.isomerase (a??s?m?re?s) n (Chemistry) any enzyme that catalyses the conversion of one isomeric form of a compound to anotherCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014i?som?er?ase (a??s?m ??re?s, -?re?z) n. any of a class of enzymes that catalyze reactions involving intramolecular rearrangements. [1940?45] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.