The Collaborative International Dictionary of English v.0.48:

Invertase \In*vert"ase\, n. (Chem.)
   (a) An enzyme capable of effecting the inversion of cane
       suger, producing invert sugar. It is found in many plants
       and in the intestines of animals.
   (b) By extension, any enzyme which splits cane sugar, milk
       sugar, lactose, etc., into monosaccharides.
       [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

invertase
    n 1: an enzyme that catalyzes the hydrolysis of sucrose into
         glucose and fructose [syn: invertase, saccharase,
         sucrase]