Purine Catabolism in Plants

Publisher Website
Google Scholar
Abstract
Inosine nucleosidase (EC 3.2.2.2), the enzyme which hydrolyzes inosine to hypoxanthine and ribose, was partially purified from L. luteus L. cv. Topaz seeds by extraction of the seed meal with low ionic strength buffer, ammonium sulfate fractionation and chromatography on amino-hexyl-Sepharose, Sephadex G-100 and hydroxyapatite. MW of the native enzyme is 62,000 as judged by gel filtration. The inosine nucleosidase exhibits optimum activity around pH 8. Energy of activation of inosine hydrolysis estimated from Arrhenius plot is 14.2 kc/mol. The Km value computed for inosine is 65 .mu.M. Among the inosine analogs tested, the following nucleosides are substrates for the lupin inosine nucleosidase: xanthosine, purine riboside (nebularine), 6-mercaptopurine riboside, 8-azainosine, adenosine, and guanosine. The ratio of the velocities measured at 500 .mu.M concentration of inosine, adenosine and guanosine was 100:11:1, respectively. Specificity (Vmax/Km) towards adenosine is 48 times lower than that towards inosine. In contrast to the adenosine nucleosidase activity which is absent from lupin seeds and appears in the cotyledons during germination (Guranowski, Pawelkiewicz 1978), the inosine nucleosidase is present in both lupin seeds and seedlings.

This publication has 37 references indexed in Scilit: