Plant Nucleases. II. Properties of Corn Ribonucleases I and II and Corn Nuclease I.

A classification system is presented to distinguish 3 corn nucleases-Ribonuclease I, Ribonuclease II, and Nuclease I-which were described in the first paper of this series. The 2 ribonucleases are specific for RNA, are endonucleases, and liberate purine and pyrimidine cyclic nucleotides from dinucleotide monophosphates as well as from RNA. Ribonuclease I and II hydrolyze the purine cyclic nucleotides to 3'-nucleotides, while Ribonuclease II may also act on the pyrimidine cyclic nucleotides. Ribonuclease II is best characterized by its molecular weight of 17,000, by a higher pH optimum than Ribonuclease I, and by its absorption onto microsomes.Nuclease I is a partially purified endonuclease which produces 5'-nucleotides from RNA, DNA, and dinucleotide monophosphates. The same enzyme may also be a 3'-nucleotidase.The corn nucleases were compared with nucleases found in other plant species.