An enzyme activity that catalyzes conversion of N6-(Δ2-isopentenyl)adenosine (i6Ado) to adenosine was detected in cultured tobacco tissue by Pačes et al. (1971) (Plant Physiol. 48, 775–778). Purification and characteristics of this enzyme in corn kernels have been studied. Only the naturally occurring cytokinins i6Ado and ribosylzeatin serve as substrates; the nucleoside or free base works equally as well. The reaction requires oxygen. An unstable intermediate appears to be the primary reaction product. This product decomposes to adenosine.The enzyme activity is greatest at pH 5–7. It is independent of added magnesium. The molecular weight of the enzyme is about 88 000. The activity of the enzyme in corn kernels increases from the time of pollination to about 21 days.A nucleoside hydrolase is isolated with i6Ado oxidase. The activities can be partially separated by G-150 gel filtration. The hydrolase is less stable than the i6Ado oxidase and frozen preparations lose their activity after 2 months, whereas i6Ado oxidase is stable under these conditions.

Transfer ribonucleic acid was hydrolyzed by acid under conditions that released the purine residues. Examination of the hydrolysate by means of ion-exchange chromatography on a sulfonic acid resin revealed the presence of a A number of articles reports the presence of amino acids or small polypeptides, apart from the amino acids attached to the acceptor end of tRNA molecules, bound to nucleic acids. Ingram and Sullivan (1962) and Akashi et al. (1965), for example, have reported the presence of amino acids bound to RNA which cannot be removed through the use of extensive deproteinizing procedures. Balk et al. (1964) and Olenick and Hahn (1964) have reported the presence of amino acids in highly purified preparations of DNA isolated from a variety of sources. The nature of the amino acid-nucleic acid linkage, however, has not been elucidated. Bogdanov et al. (1962) have reported that tRNA contains amino acids attached to the phosphate residues. Harris and Wiseman (1962) have also reported the presence of small polypeptides attached to the

N6-(Δ2-Isopentenyl)adenosine, a component of tRNA, displays biological activity in both plant and animal systems. As part of a study of the biological behavior of this nucleoside, its degradation in animal tissues has been studied. An enzyme that catalyzes conversion of this nucleoside to inosine has been partially purified from chicken bone marrow. The enzyme preparation also catalyzes conversion of adenosine to inosine at about 40 times the rate of conversion of N6-(Δ2-isopentenyl)adenosine. A series of analogues of this nucleoside has been tested as substrates. The Δ3-isomer, n-pentyl, isopentyl, and furfuryl derivatives are readily cleaved. Hydroxylated derivatives of the Δ2-isopentenyl side chain, however, do not serve as substrates. Adenosine aminohydrolase from calf intestinal mucosa also catalyzes conversion of N6-(Δ2-isopentenyl)adenosine to inosine, although in order to obtain a measurable rate, the concentration of enzyme must be about 1000 times that needed to catalyze conversion of adenosine.