ATP·ase (??t?-p???s, -?z)n. An enzyme that catalyzes the formation of ATP from ADP, inorganic phosphate, and energy, found in mitochondria and chloroplasts; adenosine triphosphatase. Also called ATP synthase.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.ATPase (?e?ti??pi??e?z) n1. (Biochemistry) adenosine triphosphatase; an enzyme that converts ATP to ADPCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ATPase (?e??ti?pi e?s, -e?z) n. adenosine triphosphatase: any of several enzymes that catalyze the hydrolysis of ATP to ADP and phosphate. [1945?50] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.