Polynucleotidase activity of animal and plant tissue phosphodiesterases

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Abstract
The purification of phosphodiesterase I from hog liver has permitted the demonstration that its properties and catalytic activity are the same as the enzyme previously purified from kidney. The liver, kidney, and snake venom phosphodiesterase I preparations were compared on the basis of their ability to hydrolyze p-nitrophenyl esters of the 5'' -phosphates of thymidine, uridine, and deoxyadenosine at pH 9 in the absence of EDTA versus the activity of potato nucleotide pyrophosphatase, which is active at pH 7 in the presence of EDTA. Kidney microsomes are similarly inactive at the lower pH. Further, the tissue and venom enzymes possess activity against pTpT, TpT [oligonucleotides derived from poly T], and ribooligonucleotides which are not attacked by the plant nucleotide pyrophosphatase. A comparison of the loss of activity during heating, rates of hydrolysis, kinetics, and competitive inhibition of the animal tissue phosphodiesterase I on several substrates indicates that 1 catalytic site is responsible for the cleavage of nucleoside 5''-phosphate from p-nitrophenyl esters, TppT, and NAD+. The tissue enzyme, like the venom enzyme, is active on the 3''-hydroxyl terminus of transfer RNA.