Oxaloacetate Synthesis in the Methanarchaeon Methanosarcina barkeri: Pyruvate Carboxylase Genes and a Putative Escherichia coli-Type Bifunctional Biotin Protein Ligase Gene (bpl/birA) Exhibit a Unique Organization
AUTOR(ES)
Mukhopadhyay, Biswarup
FONTE
American Society for Microbiology
RESUMO
Evidence is presented that, in Methanosarcina barkeri oxaloacetate synthesis, an essential and major CO2 fixation reaction is catalyzed by an apparent α4β4-type acetyl coenzyme A-independent pyruvate carboxylase (PYC), composed of 64.2-kDa biotinylated and 52.9-kDa ATP-binding subunits. The purified enzyme was most active at 70°C, insensitive to aspartate and glutamate, mildly inhibited by α-ketoglutarate, and severely inhibited by ATP, ADP, and excess Mg2+. It showed negative cooperativity towards bicarbonate at 70°C but not at 37°C. The organism expressed holo-PYC without an external supply of biotin and, thus, synthesized biotin. pycA, pycB, and a putative bpl gene formed a novel operon-like arrangement. Unlike other archaeal homologs, the putative biotin protein ligases (BPLs) of M. barkeri and the closely related euryarchaeon Archaeoglobus fulgidus appeared to be of the Escherichia coli-type (bifunctional, with two activities: BirA or a repressor of the biotin operon and BPL). We found the element Tyr(Phe)ProX5Phe(Tyr) to be fully conserved in biotin-dependent enzymes; it might function as the hinge for their “swinging arms.”
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=95260Documentos Relacionados
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