Trans-N-deoxyribosylase: substrate specificity studies. Purine bases as acceptors.

A series of purine bases and analogues were tested as substrates for trans-N-deoxyribosylase (EC 2.4.2.6). It was observed that the pyrimidine ring and its substituents on positions 1, 2 and 6, are of minor importance. On the other hand only a few modifications are tolerated on the imidazole moiety, as follows. 1. A tautomeric proton must be present on the imidazole ring. The "usual" shift is between position 9 and 7. 2. The position of the tautomeric proton governs the site of substitution. 3. For steric reasons no substituent is allowed on position 8.