Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Plant Physiology 70:344-349 (1982)
© 1982 American Society of Plant Biologists

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Purine Catabolism in Plants 1

Purification and Some Properties of Inosine Nucleosidase from Yellow Lupin (Lupinus Luteus L.) Seeds

Andrzej Guranowski

Institute of Biochemistry, Academy of Agriculture, Wolynska 35, 60-637 Poznan, Poland

Inosine nucleosidase (EC 3.2.2.2), the enzyme which hydrolyzes inosine to hypoxanthine and ribose, has been partially purified from Lupinus luteus L. cv. Topaz seeds by extraction of the seed meal with low ionic strength buffer, ammonium sulfate fractionation, and chromatography on aminohexyl-Sepharose, Sephadex G-100, and hydroxyapatite.

Molecular weight of the native enzyme is 62,000 as judged by gel filtration. The inosine nucleosidase exhibits optimum activity around pH 8. Energy of activation for inosine hydrolysis estimated from Arrhenius plot is 14.2 kilocalories per mole. The Km value computed for inosine is 65 micromolar.

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 micromolar 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 Planta 139: 245-247), the inosine nucleosidase is present in both lupin seeds and seedlings.

1 This work is dedicated to Professor Jerzy Pawelkiewicz on the occasion of his sixtieth birthday.






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