PURIFICATION AND PROPERTIES OF A RIBONUCLEASE FROM AVENA LEAF TISSUES

A ribonuclease was isolated and purified from Avena leaf tissues. The enzyme was shown to be an endonuclease which cleaves all the phosphodiester bonds forming nucleoside 2′,3′-cyclic phosphates. As shown by kinetic analysis, the ribonuclease has a preference for the secondary phosphate esters of 3′-GMP. The early release of 2′,3′-GMP was followed by the release of 2′,3′-AMP and 2′,3′-UMP, whereas a pronounced lag period proceded the releae of 2′,3′-CMP. The purine/pyrimidine ratio in the mixture of nucleotides liberated during RNA hydrolysis was high at the beginning of the reaction and gradually decreased with longer incubation time. The relative purine specificity of the enzyme was also shown by using homopolymers as substrates. A mixture of poly A and poly U in the proportion 1:2, known to produce maximum secondary interaction, was not attacked. The enzyme hydrolyzed only the purine 2′,3′-cyclic phosphates to a considerable extent. The following reaction products inhibited the enzyme: 3′-AMP, 3′-GMP, 2′,3′-AMP and 2′,3′-GMP, 3′-CMP, 3′UMP, 2′,3′-CMP and 2′,3′-UMP had no or little effect. The activity of the ribonuclease described above was found to increased rapidly in Avena leaf tissue in association with injury and/or senescence. © 1969.