denature

from The American Heritage® Dictionary of the English Language, 5th Edition.

• transitive verb To change the nature or natural qualities of.
• transitive verb To render unfit to eat or drink without destroying usefulness in other applications, especially to add methanol to (ethyl alcohol).
• transitive verb To cause the tertiary structure of (a protein) to unfold, as with heat, alkali, or acid, so that some of its original properties, especially its biological activity, are diminished or eliminated.
• transitive verb To cause the paired strands of (double-stranded DNA) to separate into individual single strands.
• transitive verb Physics To add nonfissionable matter to (fissionable material) so as to prevent use in an atomic weapon.

from The Century Dictionary.

• Same as denaturize.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To deprive of its natural qualities; change the nature of.
• transitive verb to render (ethyl alcohol) unfit to drink by adding in toxic or unpalatable substances (such as benzene or pyridine) which nevertherless permit alcohol to be used as a solvent.
• transitive verb modify the tertiary structure of (a protein or nucleic acid) so as to reduce or destroy its characteristic biological activity.
• intransitive verb To become denatured.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb To take away a natural characteristic or inherent property of a thing or a person.
• verb in reference to alcohol to add something that makes alcohol unsuitable for consumption but leaves the alcohol suitable for other purposes.
• verb chemistry To subject (especially a protein) to conditions altering its original form or state.
• verb To combine fissionable material with nonfissionable material in order to prevent its use in an atomic weapon.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb modify (as a native protein) especially by heat, acid, alkali, or ultraviolet radiation so that all of the original properties are removed or diminished
• verb make (alcohol) unfit for drinking without impairing usefulness for other purposes
• verb add nonfissionable material to (fissionable material) so as to make unsuitable for use in an atomic bomb