Studies on inhibition of adenosine deaminase by isocoformycin in vitro and in vivo.

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Abstract
Isocoformycin is a structural isomer of coformycin which is a potent inhibitor of adenosine deaminase. Isocoformycin showed a weaker inhibition of this enzyme than coformycin; the binding of coformycin to enzyme was irreversible, but isocoformycin inhibition was competitive with substrate. The Ki value of isocoformycin was 4.5 .apprx. 10 .times. 10-8 M. Following i.p. injection of isocoformycin in mice, adenosine deaminase activity of homogenates of several organs was determined and the following ED50 values (50% inhibition doses) were observed: 29 mg/kg for thymus, 13 mg/kg for spleen, 80 mg/kg for liver and 20 mg/kg for kidney. Adenosine deaminase inhibition in rabbit blood in vitro was tested in comparison with coformycin.