RESUMO
The ribonucleotide reductase from the strictly anaerobic methanogen Methanobacterium thermoautotrophicum has been partially purified by ion-exchange and gel-filtration chromatography. Its molecular weight is estimated to be 100,000 by the latter step. Unlike all previously studied ribonucleotide reductases, the enzyme does not employ dithiol compounds such as dithiothreitol as artificial electron donors in in vitro assays. Inhibition of the enzyme by S-adenosylmethionine, oxygen, and azide further distinguishes it from the Escherichia coli anaerobic enzyme, the iron- and manganese-containing, and the adenosylcobalamin-dependent enzymes. Our preliminary results suggest that this enzyme has an activation mechanism different from the known classes of ribonucleotide reductases.
Assuntos
Methanobacterium/enzimologia , Ribonucleotídeo Redutases/isolamento & purificação , Ribonucleotídeo Redutases/metabolismo , Adenosina/análogos & derivados , Adenosina/farmacologia , Azidas/farmacologia , Cromatografia por Troca Iônica , Etionina/análogos & derivados , Etionina/farmacologia , Hidroxiureia/farmacologia , Cinética , Ribonucleotídeo Redutases/antagonistas & inibidores , S-Adenosil-Homocisteína/farmacologia , S-Adenosilmetionina/farmacologia , Azida SódicaRESUMO
A strain of Acinetobacter lwoffii degraded 4-hydroxymandelic and 4-hydroxy-3-methoxymandelic acids to their corresponding benzoates, which were then hydroxylated by specific monooxygenases to yield, respectively, protocatechuic and 3-O-methylgallic acids; these were substrates for meta fission dioxygenases. The product formed from 3-O-methylgallate underwent slow spontaneous cyclization at pH 7 to release methanol.
Assuntos
Acinetobacter/metabolismo , Ácidos Mandélicos/metabolismo , Ácido Vanilmandélico/metabolismo , Acinetobacter/enzimologia , Ácido Gálico/análogos & derivados , Ácido Gálico/metabolismo , Hidroxibenzoatos/metabolismo , Metanol/metabolismo , Oxigenases/metabolismoRESUMO
Salicylate hydroxylase (salicylate 1-monooxygenase, EC 1.14.13.1) was purified from the soil yeast Trichosporon cutaneum. The enzyme contained flavin adenine dinucleotide and was monomeric, with a molecular weight of 45,300. In addition to salicylate, the four isomeric dihydroxybenzoates having one hydroxyl adjacent to carboxyl in the benzene nucleus were oxidatively decarboxylated without formation of hydrogen peroxide. One of these isomers, gentisate, was rapidly oxidized to hydroxyquinol by the enzyme but did not serve as an effective single carbon source for T. cutaneum; however, when growing with salicylate, cells also readily utilized gentisate for growth. Hydroxyquinol 1,2-dioxygenase (EC 1.13.11....) is a newly investigated enzyme which was purified from T. cutaneum grown with 4-hydroxybenzoate. The enzyme was red, contained ferric iron, and was specific for hydroxyquinol; catechol and pyrogallol were oxidized at less than 1% of the rate for hydroxyquinol, and no activity could be detected against seven other catechols. The enzyme was composed of two nonidentical subunits having molecular weights of 39,600 and 38,200 and was apparently dimeric.
