A KINETIC STUDY OF THE DEAMINATION OF SOME ADENOSINE ANALOGUES: SUBSTRATE SPECIFICITY OF ADENOSINE DEAMINASE

Abstract

The kinetic constants Kmand Vmaxwere determined for the deamination by adenosine deaminase of a series of analogues of adenosine containing "fraudulent" sugars. The configuration of the 2′-hydroxyl was found to be important for the binding of enzyme and substrate. The largest effect of changes in sugar structure was on the rate of breakdown of the enzyme–substrate complex to form products, i.e. Vmax. The nature of the configuration in the 3′-position was not important if the 2′-hydroxyl was trans to the glycosidic linkage; however, if the steric arrangement of the 2′-hydroxyl was cis to the glycosidic linkage, then Vmaxshowed a marked dependence on the nature of the 3′-substituent and its configuration. For instance, Vmaxvalues were for arabinosyl adenine < 3′-deoxyarabinosyl adenine <lyxosyl adenine. 6-N-methyladenosine was found to be a competitive inhibitor of adenosine deaminase, with a Kiof 2 × 10−6M.