Adenosine deaminase activity of chicken erythrocyte and heart cytosols

1. The adenosine deaminase (ADA) activities of chicken erythrocyte and heart cytosols had pH optima of 6.5. The temperature optima for erythrocyte and heart ADA were 30 and 35 degrees C, respectively. 2. The deoxyadenosine/adenosine deamination ratios ranged from 0.75 to 0.84 for both ADA activities. 3. For erythrocyte ADA, Km values were 8.9-12.9 microM adenosine (range) and 8.3 microM 2'-deoxyadenosine. For heart ADA, Km values were 6.7-12.0 microM adenosine (range) and 5.3 microM 2'-deoxyadenosine. 4. Inosine was a competitive inhibitor of both erythrocyte (Ki = 73 microM) and heart (Ki = 109 microM) ADA.