Some comparative studies of calf and chicken adenosine deaminase

Species differences in adenosine deaminase have been observed using relative substrate specificity (ratio of activity with deoxyadenosine to that with adenosine) as the primary criterion (2, 3, 13). These studies have centered around mammalian species and have led to the purification of enzyme from calf intestine (13). We have found that this purification procedure is not effective in the case of chicken duodena and developed a suitable procedure for partial purification. Using calf and chicken enzyme, we have compared several properties of adenosine deaminase. These enzymes can be distinguished using ratios of activities with 2,6-diaminopurine riboside and 2-fluoroadenosine to that with adenosine (in addition to the usual ratio of deoxyadenosine to adenosine). In the case of 2-fluoroadenosine there is a 17-fold difference between enzymes from the two sources. Furthermore, we observed a 10 kcal./mole difference in apparent energy of activation between the two enzymes and very different relationships between pH and V m or K m . Calf enzyme shows optimal extrapolated maximum velocities at about pH 7, whereas chicken enzyme show a minimum in this range. Michaelis constants for the calf enzyme are independent of pH, but the chicken enzyme shows a sharp increase below pH 5.5 and slight increase above pH 9.