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  • Title: The genetic control of the molybdoflavoproteins in Aspergillus nidulans. IV. A comparison between purine hydroxylase I and II.
    Author: Lewis NJ, Hurt P, Sealy-Lewis HM, Scazzocchio C.
    Journal: Eur J Biochem; 1978 Nov 02; 91(1):311-6. PubMed ID: 363427.
    Abstract:
    The purine hydroxylases I and II of Aspergillus nidulans [previously called xanthine dehydrogenases I and II: Scazzocchio, Holl and Foguelman, Eur. J. Biochem. 36, 428--445 (1973)] have been studied in crude extracts. The two enzymes differ in their substrate specificities, purine hydroxylase II being able to accept nicotinate as a substrate and unable to hydroxylate xanthine. The kinetics of inhibition with allopurinol and oxypurinol are also different, the two analogues being pseudo-irreversible inhibitors of purine hydroxylase I, while allopurinol is a competitive inhibitor of purine hydroxylase II and oxypurinol shows anti-competitive inhibition. Differences in electro-phoretic mobility and molecular size are also shown. We have failed to show the formation of hybrid purine hydroxylase I/II molecules. While a common evolutionary origin of the purine hydroxylases could be postulated, the data reveal a considerable divergence.
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