The Collaborative International Dictionary of English v.0.48:

DNase \DNase\ (d[=e]`[e^]n*[=a]s"), DNAase \DNAase\
   (d[=e]`[e^]n*[=a]"[=a]s) n. (Biochem.)
   any of numerous enzymes that catalyze the breakdown of DNA
   into oligonucleotides or mononucleotides.
   [PJC]