Uricase and Allantoinase in Glyoxysomes

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Abstract
Infat-degrading tissues ofseedlings ofsevendifferent plant species examined, uricaseactivity (urate:02 oxidoreductase, EC 1.7.33)wasassociated withparticulate fractions. After equilibrium density centrifugation on sucrosedensity gradi- entstheenzymeactivity wasrecovered intheglyoxysomal band (density: 1.25gramspercubiccentimeter). Allantoinase is alsopresent inglyoxysomes but,equally, intheproplastid region(density: 1.22gramspercubiccentimeter). Xanthine oxidase, xanthine dehydrogenase, allantoicase, andureasewere notdetected inglyoxysomes fromcastorbeanendosperm. Uricase inthese particles showsitsmaximalactivity atpH 8.9. Theapparent Km is7.4AM.Urateconcentrations greater than 120MMaswellascertain otherpurinecompoundsinhibit the enzyme.Cyanide ata concentration of10AMisa potentin- hibitor. 2,6-Dichlorophenolindophenol didnotsubstitute for oxygenaselectron acceptor.
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