Enzymatic Activity that Catalyzes Degradation of N6-(Δ2-Isopentenyl)adenosine

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Abstract
N6-(Δ2-isopentenyl)adenosine (i6A) and its analogs N6-isopentenyl, isopentyl, 4-hydroxy-3-methylbut-2-trans-enyl, and 3-hydroxy-3-methylbutyl, are competitive inhibitors of the deamination of adenosine by an adenosine amino-hydrolase [EC 3.5.4.2] isolated from chicken bone marrow. The K1 values fall in the range 1–3×10−4. The same enzyme also catalyzes conversion of i6A and other N6-(alkyl substituted) analogs to inosine. The potent inhibitor of the aminohydrolase from calf intestinal mucosa, 6-amino-9-(1-hydroxy-2-octyl)purine, inhibits degradation of both adenosine and i6A by the bone marrow enzyme; Ki 3.5x10−7 and 1.0×10−7, respectively. An assay using 8−14C−i6A as substrate was used to assay various tissues for this enzyme activity. The major site of occurrence of this enzyme is associated with the blood system. The enzyme activity was detected in chicken, pig, rabbit, and human samples. An assay based on gas chromatography was used to monitor the levels in vivo of N6-(substituted)adenosine derivatives in the blood of a rabbit. i6A is cleared from the blood in about 4 hr after administration of a single dose (intravenous, 150 mg/ kg) while the analog, N6-(3-chlorobut-2-enyl)adenosine, that is not a substrate for the enzyme, is cleared much more slowly. These results suggest that this enzyme activity contributes to the clearance of i6A from humoral blood.

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