Human erythrocytic purine nucleoside phosphorylase: reaction with sugar-modified nucleoside substrates

Abstract

The kinetic parameters (Km and Vmax) of sugar-modified analogs of inosine and guanosine were determined with human erythrocytic purine nucleoside phosphorylase (PNP). Steric alterations at the 2'' and 3'' positions greatly lessened or abolished substrate activity. However, the 5''-deoxy- and 2'',5''-dideoxy-.beta.-D-ribofuranosyl and the .alpha.-L-lyxosyl analogs were good substrates, indicating that the 5''-hydroxyl and the orientation of the 5''-hydroxymethyl group are not important for binding. The sugar phosphate analog, 5-deoxyribose 1-phosphate, was synthesized from 5''-deoxyinosine with immobilized PNP, and its presence was verified by using it in the enzymic synthesis of 5''-deoxyguanosine. The adenosine versions of the 5''-modified analogs also reacted with adenosine deaminase, at < 1% of Vmax.