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Xanthine dehydrogenase from Drosophila melanogaster: purification and properties of the wild-type enzyme and of a variant lacking iron-sulfur centers.
Biochemistry. 1992 Mar 31; 31(12):3073-83.B

Abstract

Xanthine dehydrogenase has been purified to homogeneity by conventional procedures from the wild-type strain of the fruit fly Drosophila melanogaster, as well as from a rosy mutant strain (E89----K, ry5231) known to carry a point mutation in the iron-sulfur domain of the enzyme. The wild-type enzyme had all the specific properties that are peculiar to the molybdenum-containing hydroxylases. It had normal contents of molybdenum, the pterin molybdenum cofactor, FAD, and iron-sulfur centers. EPR studies showed its molybdenum center to be quite indistinguishable from that of milk xanthine oxidase. As isolated, only about 10% of the enzyme was present in the functional form, with most or all of the remainder as the inactive desulfo form. It is suggested that this may be present in vivo. Extensive proteolysis accompanied by the development of oxidase activity took place during isolation, but dehydrogenase activity was retained. EPR properties of the reduced iron-sulfur centers, Fe-SI and Fe-SII, in the enzyme are very similar to those of the corresponding centers in milk xanthine oxidase. The E89----K mutant enzyme variant was in all respects closely similar to the wild-type enzyme, with the exception that it lacked both of the iron-sulfur centers. This was established both by its having the absorption spectrum of a simple flavoprotein and by the complete absence of EPR signals characteristic of iron-sulfur centers in the reduced enzyme. Despite the lack of iron-sulfur centers, the mutant enzyme had xanthine:NAD+ oxidoreductase activity indistinguishable from that of the wild-type enzyme. Stopped-flow measurements indicated that, as for the wild-type enzyme, reduction of the mutant enzyme was rate-limiting in turnover. Thus, the iron-sulfur centers appear irrelevant to the normal turnover of the wild-type enzyme with these substrates. However, activity to certain oxidizing substrates, particularly phenazine methosulfate, is abolished in the mutant enzyme variant. This is one of the first examples of deletion by genetic means of iron-sulfur centers from an iron-sulfur protein. The relevance of our findings both to the roles of iron-sulfur centers in other systems and to the nature of the oxidizing substrate for the Drosophila enzyme in vivo are briefly discussed.

Authors+Show Affiliations

Biochemistry Laboratory, School of Biological Sciences, University of Sussex, Brighton, U.K.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

1313286

Citation

Hughes, R K.. "Xanthine Dehydrogenase From Drosophila Melanogaster: Purification and Properties of the Wild-type Enzyme and of a Variant Lacking Iron-sulfur Centers." Biochemistry, vol. 31, no. 12, 1992, pp. 3073-83.
Hughes RK. Xanthine dehydrogenase from Drosophila melanogaster: purification and properties of the wild-type enzyme and of a variant lacking iron-sulfur centers. Biochemistry. 1992;31(12):3073-83.
Hughes, R. K. (1992). Xanthine dehydrogenase from Drosophila melanogaster: purification and properties of the wild-type enzyme and of a variant lacking iron-sulfur centers. Biochemistry, 31(12), 3073-83.
Hughes RK. Xanthine Dehydrogenase From Drosophila Melanogaster: Purification and Properties of the Wild-type Enzyme and of a Variant Lacking Iron-sulfur Centers. Biochemistry. 1992 Mar 31;31(12):3073-83. PubMed PMID: 1313286.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Xanthine dehydrogenase from Drosophila melanogaster: purification and properties of the wild-type enzyme and of a variant lacking iron-sulfur centers. A1 - Hughes,R K, PY - 1992/3/31/pubmed PY - 1992/3/31/medline PY - 1992/3/31/entrez SP - 3073 EP - 83 JF - Biochemistry JO - Biochemistry VL - 31 IS - 12 N2 - Xanthine dehydrogenase has been purified to homogeneity by conventional procedures from the wild-type strain of the fruit fly Drosophila melanogaster, as well as from a rosy mutant strain (E89----K, ry5231) known to carry a point mutation in the iron-sulfur domain of the enzyme. The wild-type enzyme had all the specific properties that are peculiar to the molybdenum-containing hydroxylases. It had normal contents of molybdenum, the pterin molybdenum cofactor, FAD, and iron-sulfur centers. EPR studies showed its molybdenum center to be quite indistinguishable from that of milk xanthine oxidase. As isolated, only about 10% of the enzyme was present in the functional form, with most or all of the remainder as the inactive desulfo form. It is suggested that this may be present in vivo. Extensive proteolysis accompanied by the development of oxidase activity took place during isolation, but dehydrogenase activity was retained. EPR properties of the reduced iron-sulfur centers, Fe-SI and Fe-SII, in the enzyme are very similar to those of the corresponding centers in milk xanthine oxidase. The E89----K mutant enzyme variant was in all respects closely similar to the wild-type enzyme, with the exception that it lacked both of the iron-sulfur centers. This was established both by its having the absorption spectrum of a simple flavoprotein and by the complete absence of EPR signals characteristic of iron-sulfur centers in the reduced enzyme. Despite the lack of iron-sulfur centers, the mutant enzyme had xanthine:NAD+ oxidoreductase activity indistinguishable from that of the wild-type enzyme. Stopped-flow measurements indicated that, as for the wild-type enzyme, reduction of the mutant enzyme was rate-limiting in turnover. Thus, the iron-sulfur centers appear irrelevant to the normal turnover of the wild-type enzyme with these substrates. However, activity to certain oxidizing substrates, particularly phenazine methosulfate, is abolished in the mutant enzyme variant. This is one of the first examples of deletion by genetic means of iron-sulfur centers from an iron-sulfur protein. The relevance of our findings both to the roles of iron-sulfur centers in other systems and to the nature of the oxidizing substrate for the Drosophila enzyme in vivo are briefly discussed. SN - 0006-2960 UR - https://www.unboundmedicine.com/medline/citation/1313286/Xanthine_dehydrogenase_from_Drosophila_melanogaster:_purification_and_properties_of_the_wild_type_enzyme_and_of_a_variant_lacking_iron_sulfur_centers_ L2 - http://flybase.org/cgi-bin/uniq.html?db=fbrf&field=pubmed_id&context=1313286 DB - PRIME DP - Unbound Medicine ER -