Adenosine deaminase (ADA) catalyzes the deamination of 2',3'-isopropylidene adenosine and the corresponding 5'-amino derivative in a 3% dimethylsulfoxide aqueous solution. Whereas ADA is unable to convert other 5'-substituted derivatives (acetate, acetamido, azide), the enzyme adenylate deaminase (AMPDA) accepts all the above compounds as substrates for their biotransformation to the corresponding 5'-substituted inosine derivatives.