AD
Adenosine + H₂O Inosine + NH₃

The enzyme is widely distributed in animal tissues (E.J. Conway and R. Cooke, Biochem J., 33, 457-479, 1939). The highest enzyme activities are found in the mucosa of the small intestine, in the appendix and the spleen (V.D. Hoagland jr. and I.R. Fisher, J. Biol. Chem., 242, 4341, 1967) and (B.M Chassy and R.J. Suhadolnik, J. Biol. Chem., 242, 3655, 1967). The enzyme is present in the cytoplasmic cell fraction and also to some extent in the nucleus (R.M. Smillie, Arch. Biochem., 67, 213, 1957) and (H.K Jordan, et al., J. Neurochem., 4, 170, 1959). The optimum pH is 7.0 to 7.4.

One unit will deaminate 1.0 &mgr;mole of adenosine to inosine per min at pH 7.4 at 25° C.

1. 0.05 M Phosphate buffer, pH 7.4.
2. Adenosine, 3.6 mg/ml dissolved in buffer.
3. Enzyme solution in buffer (1-2 U/ml).

1. Set up spectrophotometer (with strip chart and temp. control) to 265 nm and 25° C.
2. Into a cuvette, pipette the following:

Phosphate buffer	2.97 ml
Adenosine	0.01 ml

Incubate cuvette in spectrophotometer at 25° C for 5 minutes to attain temperature equillibration and then establish blank rate if any. 3. Initiate reaction by adding 0.02 ml enzyme solution.
4. Calculate E_265nm/min