An Endonuclease from Mitochondria of Neurospora crassa

From the ¹ From the Department of Biochemistry, Stanford University School of Medicine, Palo Alto, California 94304

Endonuclease activity has been found to be closely associated with mitochondria of Neurospora crassa. The evidence for this association is that: (a) the activity sediments with mitochondria even after extensive washing; (b) purified nuclease is not bound by freshly prepared mitochondria; (c) nuclease and cytochrome oxidase activities cosediment through a sucrose gradient; and (d) the mitochondria must be disrupted in order to observe significant activity. The possibility has not been eliminated, however, that this association represents the binding to mitochondria of a nuclease of extramitochondrial origin.

The enzyme has been purified from both mitochondria and crude mycelial extracts. It degrades both deoxyribonucleic and ribonucleic acids to small oligonucleotides terminated by 5'-phosphomonoester groups, is most active at 37°, between pH values of 6.0 and 7.5, requires a divalent cation (Mg⁺⁺, Mn⁺⁺, or Co⁺⁺), is inhibited by ethylenediaminetetraacetic acid, and is relatively unaffected by ß-mercaptoethanol. These catalytic properties distinguish it from the extramitochondrial nuclease previously described in N. crassa.

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